Chapter 11 · 12 hours

Electricity and Magnetism

SEE past exam questions

Past questions and answers

78 questions set from this chapter, 8 of them more than once; 4 are most repeated (set, or a close variant set, in 3 or more exams). Most repeated first.

Most repeated · 5 of 31 exams
Asked 4 times
2082 Chaitra · Gandaki · 1 mark
2081 Chaitra · Gandaki · 1 mark
2081 Chaitra · Madhesh · 1 mark
2082 Chaitra · Sudurpashchim · 1 mark

Draw current time graph of alternating current.

Similar questions: Time-current graph of 2 Hz AC (2082 Chaitra · Madhesh)

Answer

The alternating current changes its magnitude and direction continuously, so its current-time graph is a sine wave that lies alternately above and below the time axis.

 Current (I)
  +I0 |      ***                 ***
      |    **   **             **   **
    0 |---*-------*-----------*-------*------> Time (t)
      |            **       **
  -I0 |              *** ***
      |
      |<------- one cycle (T) ------->|

The part above the time axis is the current in one direction (positive).
The part below the time axis is the current in the opposite direction (negative).
One complete cycle takes the time period $T$ , and the frequency is $f=\dfrac{1}{T}$ . In Nepal $f = 50$ Hz, so $T = 0.02$ s.

Answer checked by Claude Sonnet · Oct 21, 2026

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Most repeated · 5 of 31 exams
2082 Chaitra · Madhesh · 2 marks

Draw a time current graph of alternating current having frequency 2 Hz.

Similar questions: Time-current graph of AC (2082 Chaitra · Gandaki)

Answer

A frequency of 2 Hz means 2 complete cycles per second, so the time period is $T=\frac{1}{f}=0.5$ s. The current crosses zero every 0.25 s, and one complete cycle takes 0.5 s.

 I
 +Io |    ***                 ***
     |  **   **             **   **
     | *       *           *       *
   0 |*---------*---------*---------*---------*
     |           *       *           *       *
     |            **   **             **   **
 -Io |              ***                 ***
     +----------+---------+---------+---------> t (s)
      0        0.25      0.5      0.75       1.0

Two complete sine waves are drawn in 1 second.

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Most repeated · 4 of 31 exams
Asked 4 times
2082 Chaitra · Koshi · 4 marks
2081 Shrawan · Grade increment · 2 marks
2081 Chaitra · Koshi · 2 marks
2082 Asar · Grade increment · 2 marks

Write any two differences between direct current and alternating current.

Answer

Direct current (DC)	Alternating current (AC)
Flows in one direction only.	Changes its direction periodically (50 complete cycles per second in Nepal).
Its frequency is zero.	Its frequency is 50 Hz in Nepal.
Obtained from cells, batteries and solar cells.	Obtained from AC generators (dynamos) at power stations.
Cannot be stepped up or down by a transformer.	Can easily be stepped up or down by a transformer.

(Any two of the above.)

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Most repeated · 3 of 31 exams
Asked 3 times
2082 Chaitra · Koshi · 4 marks
2082 Chaitra · Lumbini · 2 marks
2081 Chaitra · Gandaki · 1 mark
SEE 2080 model question, Set 2, Science and Technology · 2 marks

Write any two ways of increasing electricity from dynamo.
Figure: Diagram of an a.c. generator: rectangular coil rotating between N and S poles of two magnets, with slip rings, carbon brushes and terminals connected to load.

Answer

The induced emf (electricity) of a dynamo can be increased by:

Using a stronger magnet (increasing the strength of the magnetic field).
Increasing the number of turns of the coil.
Rotating the coil faster (increasing the speed of rotation).
Increasing the area of the coil.

(Any two.)

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Asked 2 times
2082 Chaitra · Madhesh · 1 mark
2081 Chaitra · Gandaki · 1 mark

A magnet as shown in the figure if inserted into the solenoid, the needle of galvanometer is deflected. What could be the reason for this?
(a) Motor effect (b) electromagnetic induction (c) Mutual induction (d) Magnetic effect of current
Figure: A solenoid coil connected to a galvanometer; a bar magnet with pole N is shown beside it, to be inserted into the solenoid.

Answer

(b) electromagnetic induction. When the magnet moves into the solenoid, the magnetic flux linked with the coil changes, so an emf and current are induced, and the galvanometer needle deflects.

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Asked 2 times
SEE 2080 model question, Set 3, Science and Technology · 2 marks
2080 Chaitra · Koshi · 2 marks
2079 Chaitra · Karnali · 2 marks

Write any two differences between electric motor and generator.

Answer

Electric motor	Generator
Converts electrical energy into mechanical energy.	Converts mechanical energy into electrical energy.
Works on the motor effect (a current-carrying conductor in a magnetic field experiences a force).	Works on electromagnetic induction.
Current is supplied to the coil from outside.	Current is produced in the coil.

(Any two.)

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Asked 2 times
2082 Chaitra · Madhesh · 1 mark
2080 Chaitra · Koshi · 1 mark

The electricity supply in your laboratory is 110 V. You have a small fan that operates on 12 V. You have two transformers.
(i) First one is with more turns in primary coil than in the secondary coil.
(ii) Second one is with fewer turns in primary coil than in secondary coil.
Which transformer should you use to safely operate the fan?

Answer

The first transformer (more turns in the primary than in the secondary) should be used.

It is a step-down transformer, which lowers the voltage: $\frac{V_s}{V_p}=\frac{N_s}{N_p}$ with $N_s<N_p$ , so $V_s<V_p$ .
The 110 V supply can therefore be reduced to 12 V.
The second transformer is a step-up transformer. It would raise 110 V to a higher value and damage the 12 V fan.

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Asked 2 times
2081 Chaitra · Koshi · 2 marks
2080 Chaitra · Bagmati · 2 marks

Draw a neat diagram of electric current production process by using a magnet and a coil.

Answer

When a magnet is moved into or out of a coil, the flux through the coil changes and an emf is induced (electromagnetic induction).

            coil (solenoid)
        _  ___________________  _
 N S -->  (@@@@@@@@@@@@@@@@@@@)  
 magnet   (@@@@@@@@@@@@@@@@@@@)
 moves in  \_______   _______/
                  |   |
                  | G |   G = galvanometer
                  +---+   (needle deflects while the magnet moves)

Magnet moving into the coil: needle deflects in one direction.
Magnet moving out: needle deflects in the opposite direction.
Magnet at rest: no deflection.

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Asked 2 times
2079 Chaitra · Madhesh · 1 mark
2079 Chaitra · Gandaki · 1 mark

Write one way to increase the magnitude of induced e.m.f. in a generator.

Answer

Rotate the coil faster. (Other ways: use a stronger magnet, or increase the number of turns of the coil.)

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2080 Chaitra · Gandaki · 4 marks

The value of output voltage is 20 times less than input voltage in the given figure.
(i) Calculate number of turns in secondary coil.
(ii) What will happen if DC is supplied in primary coil?
(iii) What will happen if the number of turns of the wire are made equal?
Figure: A transformer on a rectangular iron core with a primary coil on one side labelled 1500 (turns) and a secondary coil on the other side.

Similar questions: Transformer 750 V, 400 turns (2082 Chaitra · Karnali)

Answer

Given: $N_p=1500$ , $V_p=20\,V_s$ .

(i) $\dfrac{N_s}{N_p}=\dfrac{V_s}{V_p}=\dfrac{1}{20}$ , so $N_s=\dfrac{1500}{20}=\mathbf{75}$ turns.

(ii) If DC is supplied, the flux in the core is constant, so no emf is induced in the secondary and the output is zero. The primary may also overheat, because only its small resistance limits the current.

(iii) If the numbers of turns are equal ( $N_s=N_p$ ), then $V_s=V_p$ . The output voltage equals the input voltage, so the transformer neither steps up nor steps down the voltage.

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2081 Shrawan · Grade increment · 2 marks

A transformer has 420 turns in primary coil and 70 turns in secondary coil. Calculate the secondary voltage if the primary voltage is 210 V.

Similar questions: Transformer 6000:1000, 210 V (2082 Chaitra · Gandaki)

Answer

Given: $N_p=420$ , $N_s=70$ , $V_p=210$ V.

$V_s=V_p\times\frac{N_s}{N_p}=210\times\frac{70}{420}=35\ \text{V}$

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2082 Chaitra · Gandaki · 1 mark

A transformer has 6,000 turns in the primary coil and 1,000 turns in the secondary coil. Calculate the secondary voltage if the primary voltage is 210 V.
(a) 25 V (b) 35 V (c) 45 V (d) 55 V

Similar questions: Transformer 420:70 turns, 210 V (2081 Shrawan · Grade increment)

Answer

(b) 35 V

$V_s=V_p\times\frac{N_s}{N_p}=210\times\frac{1000}{6000}=35\ \text{V}$

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2082 Chaitra · Karnali · 4 marks

The value of output voltage is 10 times less than input voltage in the given figure:
(a) Calculate the number of turns in the secondary coil if the number of turns in the primary coil is 400.
(b) What will happen, if the number of turns is made equal in both the coils?
(c) What would be the output voltage if 12 V D.C. is supplied to the device?
Figure: Transformer diagram: primary coil labelled Primary Input with 750 V on the input side, on an iron core with a secondary coil.

Similar questions: Transformer 1500 turns, 20 times less (2080 Chaitra · Gandaki)

Answer

Given: $V_p=750$ V, $V_s=\dfrac{750}{10}=75$ V, $N_p=400$ .

(a) $N_s=N_p\times\frac{V_s}{V_p}=400\times\frac{75}{750}=\mathbf{40}$ turns.

(b) If $N_p=N_s$ , then $V_s=V_p$ . The output voltage equals the input voltage, so no step-up or step-down occurs.

(c) The output is 0 V, because 12 V DC does not produce a changing flux and so no emf is induced.

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2082 Chaitra · Gandaki · 2 marks

When a magnet is introduced into a coil, what happens to the needle of galvanometer. If the magnet is held at rest inside the coil, what will happen to the needle?

Answer

When the magnet is introduced into the coil, the magnetic flux linked with the coil changes, an emf is induced, and the galvanometer needle deflects (momentarily, as long as the magnet is moving).
If the magnet is held at rest inside the coil, the flux does not change, so no current is induced and the needle stays at zero.

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2080 Chaitra · Bagmati · 4 marks

Fill in the following table on the basis of given graph.

Properties Fig. I Fig. II
Value of current ......... .........
Condition of poles of current ......... .........
Devices in which it is used ......... .........
Any one source ......... .........
Figure: Two current-time graphs. Fig. I: current (y-axis) constant at 6 (a horizontal line at value 6) against time (x-axis). Fig. II: current against time is a sinusoidal wave alternating about the time axis with peak values marked 2 (and -2), with time marks 0.01, 0.02, 0.03 s on the axis.

Properties	Fig. I	Fig. II
Value of current	.........	.........
Condition of poles of current	.........	.........
Devices in which it is used	.........	.........
Any one source	.........	.........

Answer

Properties	Fig. I	Fig. II
Value of current	Constant, 6 A (does not change with time)	Varies continuously with time between +2 A and -2 A (peak value 2 A)
Condition of poles of current	Poles are fixed (one positive, one negative)	Poles keep changing (alternating)
Devices in which it is used	Torch, mobile phone, radio, clock	Electric fan, bulb, refrigerator, television
Any one source	Dry cell / battery / solar cell	AC generator (dynamo)

Fig. I is direct current (DC) and Fig. II is alternating current (AC).

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2080 Grade increment · 1 mark

Under which one of the following principles does the transformer work?
(a) Mutual Induction (b) Motor Effect (c) Electromagnetic Induction (d) Electromagnetic effect

Answer

(a) Mutual Induction. A changing current in the primary coil changes the flux linked with the secondary coil and induces an emf in it.

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2080 Grade increment · 4 marks

A 18 V rickshaw is charged at a charge station. It is charged through a transformer having 600 turns in primary coil, 220 V line.
(i) Calculate the number of turns in secondary coil of the transformer.
(ii) Which type of transformer is this? What is the output voltage if 1.5 V of a cell is supplied in it?

Answer

(i) Given: $N_p=600$ , $V_p=220$ V, $V_s=18$ V.

$\frac{N_s}{N_p}=\frac{V_s}{V_p}\;\Rightarrow\; N_s=\frac{V_s}{V_p}\times N_p=\frac{18}{220}\times 600\approx 49$

Number of turns in the secondary coil is about 49.

(ii) It is a step-down transformer ( $N_s<N_p$ ). If a 1.5 V cell (DC) is supplied, the output voltage is 0 V, because DC gives a steady flux and no emf is induced in the secondary.

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2080 Chaitra · Gandaki · 2 marks

Which of the current graph in the figure is applicable in functioning of a transformer? Explain with reason.
Figure: Two current-versus-time graphs: Figure A shows a constant horizontal line (direct current); Figure B shows a sinusoidal wave (alternating current) against time t.

Answer

Figure B (alternating current). A transformer works on mutual induction, which needs a changing magnetic flux. Only AC changes continuously in magnitude and direction, so it produces a changing flux in the core and induces emf in the secondary coil. DC (Figure A) is constant and gives no induced emf.

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2080 Chaitra · Gandaki · 2 marks

A diagram related with solenoid and its magnetic fields is given. Which end of it is North Pole? Justify your answer.
Figure: A solenoid (coil) with ends labelled A (top) and B (bottom); arrows mark current direction, entering at the top-right pointing right/over the coil and leaving at the bottom pointing left.

Answer

The polarity of a solenoid is found from the direction of the current at the end (clockwise or anticlockwise rule).

If the current appears anticlockwise when viewed from an end, that end is the North pole.
If it appears clockwise, that end is the South pole.

From the current directions shown in the figure, the current at the top end A flows anticlockwise as seen from that end, so A is the North pole and B is the South pole.

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2080 Chaitra · Karnali · 4 marks

A 12 V rickshaw is charged at a charge station in Dhangadhi. It is charged using a transformer having 550 turns in primary coil connected in 220 V AC, line.
(i) Calculate the number of turns in secondary coil of transformer. (ii) Mention the type of transformer used to charge rickshaw. Write down one difference between this transformer and the transformer used in power house.

Answer

(i) Given: $N_p=550$ , $V_p=220$ V, $V_s=12$ V.

$N_s=\frac{V_s}{V_p}\times N_p=\frac{12}{220}\times 550=30$

The secondary coil has 30 turns.

(ii) It is a step-down transformer. Difference: this transformer lowers the voltage (fewer turns in the secondary), whereas the transformer used in the power house is a step-up transformer that raises the voltage (more turns in the secondary).

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2080 Chaitra · Koshi · 1 mark

Which physical quantity always remains the same in a transformer?
(i) Force (ii) Voltage (iii) Current (iv) Power

Answer

(iv) Power. For an ideal transformer, input power equals output power ( $V_pI_p=V_sI_s$ ), so the power is unchanged. Voltage and current change in opposite ways.

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2080 Chaitra · Koshi · 1 mark

If number of turns of wire in primary coil of a transformer shown in the diagram is 4 times more than that in secondary coil. What will be the value of secondary voltage?
(i) 1110 V (ii) 220 V (iii) 110 V (iv) 55 V
Figure: Diagram of a transformer: a rectangular iron core with a primary coil on the left limb connected to a 220 V input and a secondary coil on the right limb.

Answer

(iv) 55 V

$V_s=V_p\times\frac{N_s}{N_p}=220\times\frac{1}{4}=55\ \text{V}$

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2080 Chaitra · Lumbini · 1 mark

What is the major similarity in electric motor and current generator?
(a) Both need AC input in their coil (b) Both need DC input in their coil (c) Coil of both is made of enamelled wire (d) Coil of both is made of non-enamelled wire

Answer

(c) Coil of both is made of enamelled wire. In both machines the copper coil is insulated with enamel so that adjacent turns do not short-circuit. (A motor needs DC input and a generator gives AC, so (a) and (b) are wrong.)

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2080 Chaitra · Lumbini · 4 marks

When 220 V is passed in the primary coil of a transformer, 440 V is induced in secondary coil. If the number of turns in secondary coil is 350:
(i) What will be the number of turns in primary coil?
(ii) What will happen if core of a transformer is not laminated?
(iii) Can it be used by connecting with battery?

Answer

Given: $V_p=220$ V, $V_s=440$ V, $N_s=350$ .

(i) $N_p=N_s\times\frac{V_p}{V_s}=350\times\frac{220}{440}=\mathbf{175}$ turns.

(ii) If the core is not laminated, large eddy currents flow in it. These heat the core and waste energy, so the efficiency falls.

(iii) No. A battery gives DC, which produces no changing flux, so no emf is induced in the secondary.

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2080 Chaitra · Madhesh · 1 mark

What amount of current can flow in the kettle written with 750 watt and 220 V?
(a) 3 A (b) 3.4 A (c) 5 A (d) 7 A

Answer

(b) 3.4 A

$P=VI\Rightarrow I=\dfrac{P}{V}=\dfrac{750}{220}=3.41\ \text{A}$

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2080 Chaitra · Madhesh · 1 mark

Which one is the way to increase the magnitude of induced emf in a generator?
(a) By increasing the length of magnet (b) By increasing the distance between the coil and the magnet. (c) By increasing the strength of magnetic field (d) By decreasing the speed of rotation

Answer

(c) By increasing the strength of magnetic field. Induced emf grows with a stronger field, more turns, larger coil area and faster rotation. Increasing the distance or decreasing the speed lowers it.

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2080 Chaitra · Madhesh · 1 mark

What will you do to increase the magnetic flux for the coil without changing the magnetic field of the bar magnet?
Figure: A bar magnet (S on left, N on right) with magnetic field lines spreading out from the N pole toward a single-loop coil placed to the right of the magnet.

Answer

Magnetic flux $\Phi=BA\cos\theta$ . Without changing the magnet, bring the coil closer to the pole (where the field is stronger), or use a coil of larger area held perpendicular to the field lines (or increase the number of turns).

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2080 Chaitra · Madhesh · 2 marks

Write the unit of current electricity and pressure.

Answer

Unit of current electricity (electric current): ampere (A).
Unit of pressure: pascal (Pa).

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2080 Chaitra · Madhesh · 2 marks

A model of DC motor as shown in the diagram was made by Rakesh. He removed the enamels of the ends of the coil and used new cell. When he brought a magnet close to the coil it did not move although there was no problem in circuit? What might be the possible causes of it? Mention any two of them.
Figure: Photograph of a simple DC motor model: a coil suspended/supported on two supports above a cell (battery) with connecting wires.

Answer

Possible causes:

The enamel was removed from both halves of the ends of the coil. For a DC motor the enamel should be removed from only one half (one side) of each end, so that the current is cut off every half turn and the coil keeps turning. Otherwise it stops after a half turn.
The magnet was too weak or too far, so the force on the coil was too small to turn it.
Poor contact or too much friction at the supports.

(Any two.)

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2080 Chaitra · Sudurpashchim · 2 marks

What is the frequency of DC? Why?

Answer

The frequency of DC is zero. DC flows in one direction only and does not change its direction or magnitude with time, so it has no cycles per second.

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2080 Chaitra · Sudurpashchim · 4 marks

An electric material production company saw the demand of transformer in the market.
(i) If the company manufactures transformers with number of primary coil 200 turns and secondary coil 100 turns. What type of transformer is formed?
(ii) If 50V DC is passed in the primary coil in the transformer manufactured by the company, what will be the secondary voltage?
(iii) What is the relation between input and output energy in the transformers?
(iv) What is the use of transformer given in no. 'i', in our daily life?

Answer

(i) $N_p=200>N_s=100$ , so it is a step-down transformer.

(ii) The secondary voltage is 0 V, because DC does not produce a changing flux and so no emf is induced.

(iii) For an ideal transformer, input energy (power) equals output energy: $V_pI_p=V_sI_s$ . In practice the output is slightly less because of losses.

(iv) It is used in mobile chargers and adapters to reduce the 220 V supply to a low voltage.

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2081 Chaitra · Bagmati · 1 mark

Which of the following fact is correct?
(a) Electric motor changes electrical energy into kinetic energy (b) Electric generator changes electrical energy in to mechanical energy. (c) Both electric motor and generator work on same principle. (d) Both electric motor and generator changes mechanical energy into electrical energy

Answer

(a) An electric motor changes electrical energy into kinetic (mechanical) energy. A generator does the opposite, and the two work on different principles (motor effect and electromagnetic induction).

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2081 Chaitra · Bagmati · 4 marks

(i) When 240 V is passed in the primary coil of a transformer, 480 V is induced in secondary coil, if there are 300 turns in primary coil how many turns will be in secondary coil?
(ii) Why is the core of a transformer laminated?
(iii) Can transformer be used in DC circuit? Give reason.

Answer

(i) $N_s=N_p\times\frac{V_s}{V_p}=300\times\frac{480}{240}=\mathbf{600}$ turns.

(ii) The core is laminated (made of thin insulated sheets) to reduce eddy currents, which would otherwise heat the core and waste energy.

(iii) No. DC gives a constant magnetic flux, so there is no induced emf in the secondary. A transformer works only on AC.

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2081 Shrawan · Grade increment · 1 mark

Write the law of electromagnetic induction.

Answer

Faraday's law: whenever the magnetic flux linked with a coil changes, an emf is induced in the coil. The magnitude of the induced emf is directly proportional to the rate of change of magnetic flux.

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2081 Chaitra · Gandaki · 2 marks

If number of primary turns is 300, calculate the number of turns in the secondary coil in the given figure.
Figure: Transformer with a core, primary winding with input 220 V A.C. mains and secondary winding with output 44 V A.C.; primary turns = 300.

Answer

Given: $N_p=300$ , $V_p=220$ V, $V_s=44$ V.

$N_s=N_p\times\frac{V_s}{V_p}=300\times\frac{44}{220}=60$

The secondary coil has 60 turns.

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2081 Chaitra · Karnali · 1 mark

What is magnetic field?

Answer

The magnetic field is the region around a magnet (or a current-carrying conductor) in which its magnetic force can be felt by another magnet or magnetic material.

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2081 Chaitra · Karnali · 4 marks

Study the given figure.
(i) Name the type of transformers X and Y.
(iii) Write any two problems of transmitting electricity the way shown in figure A.
Figure: Figure A: electric power station connected directly by wires (Fig 1) to a house. Figure B: power station with transformer X near the station, long lines, and transformer Y near the house (Fig 2). Part (ii) is not visible in the scanned copy.

Answer

(i) X is a step-up transformer (near the power station, raises the voltage). Y is a step-down transformer (near the house, lowers the voltage to 220 V).

(iii) Problems of transmitting electricity as in Figure A (directly at low voltage):

The current is large, so a lot of energy is lost as heat ( $I^2R$ ) in the long wires.
There is a large voltage drop along the lines, so houses far away receive low voltage. Very thick, costly wires would be needed to avoid this.

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2081 Chaitra · Koshi · 1 mark

When an alternating current of 60 Hz frequency is connected to the primary coil of a transformer, what will be the frequency of alternating current in the secondary coil?

Answer

60 Hz. A transformer changes the voltage and current but not the frequency, so the secondary has the same frequency as the primary.

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2081 Chaitra · Lumbini · 1 mark

If a current carrying conductor is placed in a permanent magnetic field, the conductor vibrates. What is such effect called?
(a) Magnetic effect (b) Effect of Electromagnetic induction (c) Mutual Induction effect (d) Motor effect

Answer

(d) Motor effect. A current-carrying conductor in a magnetic field experiences a force, which makes it move or vibrate.

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2081 Chaitra · Lumbini · 4 marks

The number of secondary coil is 10 times the primary coil in a transformer. If the transformer is connected to 230 V main line, how much secondary voltage is obtained? What type of transformer is this? Write a use of such transformer.

Answer

Given: $N_s=10N_p$ , $V_p=230$ V.

$V_s=V_p\times\frac{N_s}{N_p}=230\times10=2300\ \text{V}$

It is a step-up transformer. Use: in power stations to raise the voltage for long-distance transmission.

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2081 Chaitra · Madhesh · 4 marks

A transformer in a power house has 1:80 ratio of primary and secondary coils. If 400 V is passed into the primary coil what could be the voltage produced in the secondary coil? Can this transformer be used in domestic circuit?

Answer

Given: $N_p:N_s=1:80$ , $V_p=400$ V.

$V_s=400\times\frac{80}{1}=32000\ \text{V}$

The secondary voltage is 32,000 V (32 kV). It cannot be used in a domestic circuit, because this voltage is far too high (dangerous) for household appliances, which work at 220 V.

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2081 Chaitra · Sudurpashchim · 1 mark

Give one reason why wire vibrates when current/electricity is passed through the coil of the wire.
Figure: A bar magnet (S on left, N on right) with an arrow pointing toward a coil of wire connected in a closed circuit with a galvanometer/bulb.

Answer

Because of the motor effect: a current-carrying wire placed in a magnetic field experiences a force, which makes it move or vibrate.

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2081 Chaitra · Sudurpashchim · 2 marks

What type of transformer is shown in the figure? If the potential difference in A is 700 V, calculate the voltage produced in coil B.
Figure: Transformer: primary coil A with n_p = 1000 turns, secondary coil B with n_s = 50 turns, on a common core.

Answer

Since $N_p=1000>N_s=50$ , it is a step-down transformer.

$V_B=V_A\times\frac{N_s}{N_p}=700\times\frac{50}{1000}=35\ \text{V}$

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2081 Chaitra · Sudurpashchim · 2 marks

Name an instrument in which electro-magnet is used, and write a use of that instrument.

Answer

An electric bell uses an electromagnet. When the switch is pressed, the electromagnet attracts the iron armature so that the hammer strikes the gong and produces sound. (A crane also uses an electromagnet to lift iron scrap.)

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2082 Chaitra · Bagmati · 1 mark

What type of energy transformation is done by the given instrument? (i) Chemical to electrical energy. (ii) Electrical to light energy (iii) Magnetic to electrical energy (iv) Electrical to magnetic energy
Figure: A bicycle dynamo mounted against the rim of a wheel, with its small roller touching the tyre.

Answer

(iii) Magnetic to electrical energy. The dynamo is turned by the wheel (mechanical energy), and the rotating magnet changes the flux through its coil, which induces an electric current.

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2082 Chaitra · Bagmati · 4 marks

(a) A microwave oven has written "Number of secondary windings : Number of primary windings = 10:1". If the microwave oven is connected to a source of 220 V, calculate the secondary voltage obtained from the transformer. (b) Which type of transformer is this? Draw the model figure of such transformer.

Answer

(a) $N_s:N_p=10:1$ , $V_p=220$ V.

$V_s=V_p\times\frac{N_s}{N_p}=220\times10=2200\ \text{V}$

(b) It is a step-up transformer.

 Primary (few turns)      Secondary (many turns)
   220 V        +--------+      2200 V
  ----> ~~~~  |  core  |  ~~~~~~~~~~ ---->
       |@@@@|--|        |--|@@@@@@@@@@|
        ~~~~  +--------+  ~~~~~~~~~~
   Np (1)  <  Ns (10)

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2082 Asar · Grade increment · 1 mark

Which type of energy conversion occurs in a generator?
(a) Mechanical energy into electrical energy. (b) Magnetic energy into electrical energy. (c) Electrical energy into mechanical energy. (d) Magnetic energy into mechanical energy.

Answer

(a) Mechanical energy into electrical energy. The coil (or magnet) is rotated by mechanical means and the changing flux induces electric current.

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2082 Asar · Grade increment · 2 marks

In a transformer the ratio of number of turns in primary coil and in secondary coil is 1:15. If such transformer is connected to 220 V power supply, calculate secondary voltage obtained from the transformer.

Answer

Given: $N_p:N_s=1:15$ , $V_p=220$ V.

$V_s=V_p\times\frac{N_s}{N_p}=220\times15=3300\ \text{V}$

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2082 Chaitra · Gandaki · 1 mark

Write any one difference between the following figures on the basis of their working principles.
Figure: Figure A: a coil/armature rotating between the N and S poles of a permanent magnet, connected to a galvanometer (labelled Permanent magnet, Magnetic field, Galvanometer, points A, B, C). Figure B: a horseshoe magnet supported on a wooden block, with a wire connected through a switch to a battery/meter.

Answer

Figure A is a generator and works on electromagnetic induction (the coil rotating in a magnetic field produces current, mechanical to electrical energy). Figure B works on the motor effect (a current-carrying conductor in a magnetic field experiences a force, electrical to mechanical energy).

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2082 Chaitra · Karnali · 1 mark

Which of the following is the source of Alternating current?
(a) dry cell (b) solar panel (c) dynamo (d) voltaic cell

Answer

(c) dynamo. A dynamo (AC generator) produces alternating current. Dry cells, solar panels and voltaic cells give DC.

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2082 Chaitra · Karnali · 1 mark

Identify a dependent variable in Ohm's law $V=IR$ .

Answer

In Ohm's law, $V=IR$ (at constant temperature, constant $R$ ), the potential difference $V$ is changed and the current $I$ responds. So the dependent variable is the current ( $I$ ).

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2082 Chaitra · Koshi · 1 mark

If a transformer has more turns in the secondary winding than in the primary winding, which of the following statements is correct?
(a) It does not change A.C. voltage. (b) It decreases A.C. voltage. (c) It increases A.C. voltage. (d) It increases A.C. voltage according to the situation.

Answer

(c) It increases A.C. voltage. With $N_s>N_p$ , $V_s=V_p\times\frac{N_s}{N_p}>V_p$ , so it is a step-up transformer.

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2082 Chaitra · Lumbini · 1 mark

What is meant by 'the frequency of alternating current in our country is 50 Hz?

Answer

It means that the alternating current completes 50 cycles in one second, i.e. it changes direction 100 times per second.

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2082 Chaitra · Lumbini · 2 marks

A charger has a transformer which reduces supply voltage from 220 V to 5 V. Calculate the ratio of number of turns in the primary coil to that of the secondary coil.

Answer

Given: $V_p=220$ V, $V_s=5$ V.

$\frac{N_p}{N_s}=\frac{V_p}{V_s}=\frac{220}{5}=44$

The ratio $N_p:N_s=\mathbf{44:1}$ .

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2082 Chaitra · Madhesh · 1 mark

Based on which principle does the given device work?
Figure: A bicycle wheel with a small dynamo (generator) mounted against the rim.

Answer

The dynamo works on the principle of electromagnetic induction: when the magnet rotates inside the coil, the magnetic flux linked with the coil changes and an emf is induced.

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2082 Chaitra · Sudurpashchim · 4 marks

The number of turns in the secondary coil is 50 times more than that of primary coil. Calculate the output voltage, if 220 V input voltage is passed through this transformer. Which type of transformer is this? Where is such transformer used?

Answer

Given: $N_s=50N_p$ , $V_p=220$ V.

$V_s=V_p\times\frac{N_s}{N_p}=220\times50=11000\ \text{V}$

It is a step-up transformer. It is used in power stations to raise the voltage for long-distance transmission.

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2079 Chaitra · Koshi · 1 mark

Which type of voltage is transformed by a transformer?

Answer

A transformer changes alternating (AC) voltage; it does not work with direct current.

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2079 Chaitra · Bagmati · 1 mark

What is the electric device called that converts kinetic energy into electric energy?

Answer

A generator (dynamo). It converts the kinetic energy of rotation into electric energy.

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2079 Chaitra · Lumbini · 1 mark

What does an inverter do?

Answer

An inverter converts the direct current (DC) stored in a battery into alternating current (AC), so that AC appliances can run when the mains supply is off.

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2079 Chaitra · Koshi · 2 marks

An electrical appliance is shown in the diagram.
Figure: Transformer with primary coil of 100 turns at 220 V and secondary coil at 55 V.
(a) On which principle is it based? (b) Calculate the number of turns in the secondary coil.

Answer

(a) It is based on the principle of mutual induction: a changing current in the primary coil produces a changing magnetic flux, which induces an e.m.f. in the secondary coil.

(b) Given: $N_p=100$ , $V_p=220$ V, $V_s=55$ V.

$\frac{V_s}{V_p}=\frac{N_s}{N_p}\;\Rightarrow\; N_s=\frac{55}{220}\times 100=25$

The secondary coil has $25$ turns (a step-down transformer).

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2079 Chaitra · Madhesh · 2 marks

Nichrome wire is used in a heater. Why? Write any two reasons.

Answer

Nichrome wire is used in a heater because:

It has a high resistivity, so it produces a large amount of heat when current flows through it.
It has a high melting point and does not oxidise (burn) easily when red-hot, so it lasts long.

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2079 Chaitra · Gandaki · 2 marks

Inert gas is filled inside a filament lamp. Why? Write any two points.

Answer

An inert gas (such as argon or nitrogen) is filled in a filament lamp because:

It prevents the oxidation (burning) of the tungsten filament, because there is no oxygen to react with the hot filament.
It reduces evaporation of the filament, so the filament lasts longer and the bulb does not blacken quickly.

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2079 Chaitra · Lumbini · 2 marks

Between a filament lamp and a CFL, which one helps to minimize load shedding and why?

Answer

A CFL helps to minimize load shedding. A CFL gives the same brightness while using much less electric power than a filament lamp (for example, about $15$ W instead of $60$ W). Less electricity is used overall, so the load on the supply falls and there is less need for load shedding.

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2079 Chaitra · Sudurpashchim · 2 marks

Group A: Battery box, enamelled copper wire, iron nail, pin and tape. Group B: Battery box, enamelled copper wire, magnet, tape, paper clip. If a teacher instructs the groups to prepare different models to show different effects of electricity, what suitable models can be prepared by groups A and B?

Answer

Group A can make an electromagnet. The enamelled copper wire is wound around the iron nail and connected to the battery. When current flows, the nail becomes a magnet and attracts pins (magnetic effect of electric current).

Group B can make a simple electric motor. A coil of enamelled wire is made, supported on the paper clips connected to the battery and placed over the magnet. When current flows, the coil experiences a force in the magnetic field and rotates (motor effect, a magnetic effect of electric current).

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2079 Chaitra · Karnali · 3 marks

Study the given diagram and answer the following questions.
Figure: A coil between the poles of a magnet connected to a battery/galvanometer.
(a) Model of which device is shown in the diagram if a magnet is also used in it? (b) What should be done to feel the effect shown by the device? (c) Mention any two household electrical appliances based on this principle.
OR
In which principle does the dynamo work? What can we do to increase the amount of electricity produced by it? Write in two points.

Answer

(a) The diagram shows a model of an electric motor (a coil between the poles of a magnet connected to a battery).

(b) Current must be passed through the coil from the battery (complete the circuit). The coil then experiences a force in the magnetic field and rotates, which is the effect shown by the motor.

(c) Electric fan and mixer/grinder (also washing machine, water pump).

A dynamo works on the principle of electromagnetic induction. The amount of electricity produced can be increased by:

rotating the coil faster, and
using a stronger magnet (or increasing the number of turns in the coil).

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2079 Chaitra · Sudurpashchim · 3 marks

We have two transformers as below. (A) The number of primary turns is greater than that of secondary turns. (B) The number of primary turns is less than that of secondary turns.
(a) Which is the step up transformer between A and B? (b) To play a radio of 12 V with our electric line of 220 V, which transformer can we use? Explain with reason.

Answer

(a) B is the step-up transformer, because its secondary coil has more turns than its primary coil, so it increases the voltage.

(b) We can use transformer A. The radio needs $12$ V, which is lower than the $220$ V supply, so the voltage must be stepped down. In a step-down transformer the primary has more turns than the secondary:

$\frac{N_s}{N_p}=\frac{V_s}{V_p}=\frac{12}{220}<1$

Hence $N_p>N_s$ , which is transformer A.

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2079 Chaitra · Bagmati · 4 marks

A transformer is shown in the diagram.
Figure: A transformer with primary and secondary coils on a soft iron core.
(a) Clarify the cause of not making the same number of turns in the primary and secondary coils in this transformer. (b) What will be the output if D.C. of 3 V is passed in the primary coil of the transformer? (c) If the number of turns in the secondary coil is 1/5th of the number of turns in the primary coil, how much input voltage should be supplied to get 12 V output voltage?
OR
(a) Write the reason that the number of turns in the primary and secondary coils is not made equal. (b) If 3 V D.C. current is passed into a primary coil of a transformer, what will be the output in the secondary coil? (c) Write any two differences between step up and step down transformers.

Answer

(a) If the numbers of turns were equal, the output voltage would equal the input voltage. A transformer is used to change (step up or step down) voltage, so the numbers of turns must be different.

(b) The output will be zero. A DC current gives a constant magnetic flux in the core, and a changing flux is needed to induce an e.m.f. in the secondary coil. A transformer works only with AC.

(c) Given: $N_s=\frac{1}{5}N_p$ , $V_s=12$ V.

$\frac{V_s}{V_p}=\frac{N_s}{N_p}=\frac{1}{5}\;\Rightarrow\; V_p=5\times 12=60\text{ V}$

An input of $60$ V (AC) is needed.

OR (c)

Step-up transformer	Step-down transformer
Secondary turns are more than primary turns	Secondary turns are fewer than primary turns
Increases the voltage (and decreases the current)	Decreases the voltage (and increases the current)

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CDC model paper 2080, Science and Technology · 1 mark

What happen when bar magnet is placed inside solenoid at rest?
Figure: A bar magnet (N and S poles marked) inside a solenoid whose ends are connected to a galvanometer.

Answer

When the bar magnet is at rest inside the solenoid, there is no change in the magnetic flux linked with the coil. So no emf or current is induced and the galvanometer shows no deflection (zero).

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CDC model paper 2080, Science and Technology · 2 marks

Prove that electric resistance ( $\Omega$ ) $= kg\,m^2 s^{-3} A^{-2}$ .

Answer

Resistance $R=\dfrac{V}{I}$ and potential difference $V=\dfrac{W}{Q}$ .

Work $W = F\times d$ = (kg m s $^{-2}$ ) × m = kg m $^2$ s $^{-2}$
Charge $Q = I\times t$ = A s
$V=\dfrac{W}{Q}=\dfrac{\text{kg m}^2\text{s}^{-2}}{\text{A s}}=\text{kg m}^2\text{s}^{-3}\text{A}^{-1}$
$R=\dfrac{V}{I}=\dfrac{\text{kg m}^2\text{s}^{-3}\text{A}^{-1}}{\text{A}}$

$\Omega=\text{kg m}^2\text{s}^{-3}\text{A}^{-2}$

Hence proved.

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SEE 2080 model question, Set 2, Science and Technology · 2 marks

Prove that the unit of potential difference (V) = $\text{kg m}^2\text{s}^{-3}\text{A}^{-1}$

Answer

Potential difference $V=\dfrac{W}{Q}$ , where $W$ is work done and $Q$ is charge.

$W=F\times d$ . Force has unit kg m s $^{-2}$ (newton), so $W$ = kg m s $^{-2}$ × m = kg m $^2$ s $^{-2}$ (joule).
$Q=I\times t$ = A s.

$V=\frac{\text{kg m}^2\text{s}^{-2}}{\text{A s}}=\text{kg m}^2\text{s}^{-3}\text{A}^{-1}$

Hence proved.

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CDC model paper 2080, Science and Technology · 2 marks

Study the given figure and answer the following questions. i. What type of transformer is shown in the figure? ii. Why is this used in power station?
Figure: A transformer with a primary coil (INPUT) with fewer turns on the left limb and a secondary coil (OUTPUT) with more turns on the right limb of an iron core. Labels: Primary coil, Secondary coil, INPUT, OUTPUT.

Answer

i. It is a step-up transformer, because the secondary coil has more turns than the primary coil, so the output voltage is greater than the input voltage.

ii. It is used in a power station to raise the generated voltage before transmission. At high voltage the current is low (power $P=VI$ is constant), so the heat loss ( $I^2R$ ) in the long transmission lines is small.

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CDC model paper 2080, Science and Technology · 2 marks

Niva made the device as shown in figure but rate of rotation of coil is found less. What should be done to increase rate of rotation of coil? Write any two methods.
Figure: Simple homopolar motor: a cell with a magnet attached at its bottom hangs from a support, with a copper wire coil/loop touching its top terminal and the magnet.

Answer

The rotation can be increased by:

Using a stronger magnet (stronger magnetic field gives a larger force on the current-carrying wire).
Using a cell of higher voltage, or a fresh cell, or more cells in series (larger current gives a larger force).

(Also, reducing friction at the contact points helps.)

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SEE 2080 model question, Set 1, Science and Technology · 2 marks

Lamp is lit in the running bicycle by the help of a dynamo but it goes off when bicycle is stopped. Give reason.

Answer

A dynamo produces emf by electromagnetic induction, which needs a changing magnetic flux through the coil. When the bicycle stops, the dynamo head stops rotating, so there is no change in flux. No emf or current is produced, and the lamp goes off.

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SEE 2080 model question, Set 1, Science and Technology · 2 marks

In domestic house hold wiring voltage of 220 V is supplied. A battery of mobile works with 3.7 V. Draw net diagram of transformer used in mobile charger.

Answer

The charger uses a step-down transformer (220 V to about 3.7 V or a little more), so the secondary coil has far fewer turns than the primary.

   Primary (many turns)     Core     Secondary (few turns)
  220 V AC     ~~~~~~~~  +--------+  ~~~~
  --------->  |@@@@@@@@|-|        |-|@@@@|-----> about 3.7 V
  input        ~~~~~~~~  +--------+  ~~~~        output
      Np  >  Ns        Vp (220 V) > Vs (3.7 V)

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SEE 2080 model question, Set 2, Science and Technology · 1 mark

A fan in a room rotates when its switch is made on. Which principle is used here?

Answer

The motor effect. A current-carrying coil placed in a magnetic field experiences a force and rotates, so the electric motor of the fan turns.

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SEE 2080 model question, Set 2, Science and Technology · 2 marks

Write an application of step up transformer and step-down transformer each.

Answer

Step-up transformer: used at power stations to raise the voltage for long-distance transmission (reduces power loss).
Step-down transformer: used in mobile chargers and adapters (and at local substations) to reduce 220 V to a low voltage.

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SEE 2080 model question, Set 3, Science and Technology · 1 mark

What change occurs in output voltage if the number of turns in secondary coils is less than number of turns in primary coil? Write the reason.

Answer

The output voltage decreases (it becomes lower than the input). The reason is $\frac{V_s}{V_p}=\frac{N_s}{N_p}$ ; if $N_s<N_p$ then $V_s<V_p$ , so it works as a step-down transformer.

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SEE 2080 model question, Set 3, Science and Technology · 2 marks

If the load transmission at Dhalkebar, Dhanusha transmits electricity of 400 KV, then which type of transformer is used here? Also, draw figure showing primary (input) coil and secondary (output) coil in it.

Answer

A step-down transformer is used at Dhalkebar, Dhanusha. Dhalkebar is a substation where the high transmission voltage of (400,\text{kV}) is received and stepped down to a lower voltage for distribution. In a step-down transformer, the secondary coil has fewer turns than the primary coil, so (V_s < V_p).

 Primary (input)                Secondary (output)
 many turns, 400 kV             few turns, low V
    ~~~~~~~~~~~                    ~~~~
 --|@@@@@@@@@@@|----[ core ]----|@@@@|-----> to distribution
    ~~~~~~~~~~~                    ~~~~
     Np > Ns

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Questions from SEE 2082 Science and Technology, 1041 Koshi (Board exam, Chaitra 2082 (scanned PDF, bilingual)), SEE 2082 Science and Technology, 1041 Madhesh (Board exam, Chaitra 2082 (scanned PDF, bilingual)), SEE 2082 Science and Technology, 1041 Bagmati (Board exam, Chaitra 2082 (scanned PDF, bilingual)), SEE 2082 Science and Technology, 1041 Gandaki (Board exam, Chaitra 2082 (scanned PDF, bilingual)), SEE 2082 Science and Technology, 1041 Lumbini (Board exam, Chaitra 2082 (scanned PDF, bilingual)), SEE 2082 Science and Technology, 1041 Karnali (Board exam, Chaitra 2082 (scanned PDF, bilingual)), SEE 2082 Science and Technology, 1041 Sudurpashchim (Board exam, Chaitra 2082 (scanned PDF, bilingual)), SEE 2081 Science and Technology, 1041 Koshi (Board exam, Chaitra 2081 (PDF; official answer keys exist on the bidhyamandir page)), SEE 2081 Science and Technology, 1041 Madhesh (Board exam, Chaitra 2081 (PDF; official answer keys exist on the bidhyamandir page)), SEE 2081 Science and Technology, 1041 Bagmati (Board exam, Chaitra 2081 (PDF; official answer keys exist on the bidhyamandir page)), SEE 2081 Science and Technology, 1041 Gandaki (Board exam, Chaitra 2081 (PDF; official answer keys exist on the bidhyamandir page)), SEE 2081 Science and Technology, 1041 Lumbini (Board exam, Chaitra 2081 (PDF; official answer keys exist on the bidhyamandir page)), SEE 2081 Science and Technology, 1041 Karnali (Board exam, Chaitra 2081 (PDF; official answer keys exist on the bidhyamandir page)), SEE 2081 Science and Technology, 1041 Sudurpashchim (Board exam, Chaitra 2081 (PDF; official answer keys exist on the bidhyamandir page)), SEE 2080 Science and Technology, 1041 Koshi (Board exam, 2080 (scanned PDF, bilingual)), SEE 2080 Science and Technology, 1041 Madhesh (Board exam, 2080 (scanned PDF, bilingual)), SEE 2080 Science and Technology, 1041 Bagmati (Board exam, 2080 (scanned PDF, bilingual)), SEE 2080 Science and Technology, 1041 Gandaki (Board exam, 2080 (scanned PDF, bilingual)), SEE 2080 Science and Technology, 1041 Lumbini (Board exam, 2080 (scanned PDF, bilingual)), SEE 2080 Science and Technology, 1041 Karnali (Board exam, 2080 (scanned PDF, bilingual)), SEE 2080 Science and Technology, 1041 Sudurpashchim (Board exam, 2080 (scanned PDF, bilingual)), SEE 2082 Science and Technology, GI-1041 (grade increment) (Grade increment, Asar 2083 (PDF)), SEE 2081 Science and Technology, GI-1041 (grade increment) (Grade increment 2081 (8 page images); month taken from the August 2025 post, check), SEE 2080 Science and Technology, GI-1041 (grade increment) (Grade increment 2080 (PDF)), CDC model paper 2080, Science and Technology (with answer key) (Official CDC model paper, pages 2-9; answer key pages 10-15), SEE 2080 model question, Set 1, Science and Technology (Model paper Set 1 (typed PDF, publisher not named, no answers)), SEE 2080 model question, Set 2, Science and Technology (Model paper Set 2 (typed PDF, publisher not named, no answers)), SEE 2080 model question, Set 3, Science and Technology (Model paper Set 3 (typed PDF, publisher not named, no answers)), SEE 2079 Compulsory Science (RE-111) Koshi (Board exam, Chaitra 2079 (2023), last year of the old course (scanned PDF, bilingual, 75 marks); only questions that fit the current outline were taken), SEE 2079 Compulsory Science (RE-111) Madhesh (Board exam, Chaitra 2079 (2023), last year of the old course (scanned PDF, bilingual, 75 marks); only questions that fit the current outline were taken), SEE 2079 Compulsory Science (RE-111) Bagmati (Board exam, Chaitra 2079 (2023), last year of the old course (scanned PDF, bilingual, 75 marks); only questions that fit the current outline were taken), SEE 2079 Compulsory Science (RE-111) Gandaki (Board exam, Chaitra 2079 (2023), last year of the old course (scanned PDF, bilingual, 75 marks); only questions that fit the current outline were taken), SEE 2079 Compulsory Science (RE-111) Lumbini (Board exam, Chaitra 2079 (2023), last year of the old course (scanned PDF, bilingual, 75 marks); only questions that fit the current outline were taken), SEE 2079 Compulsory Science (RE-111) Karnali (Board exam, Chaitra 2079 (2023), last year of the old course (scanned PDF, bilingual, 75 marks); only questions that fit the current outline were taken) and SEE 2079 Compulsory Science (RE-111) Sudurpashchim (Board exam, Chaitra 2079 (2023), last year of the old course (scanned PDF, bilingual, 75 marks); only questions that fit the current outline were taken). Answers are written for this site; check them against your class notes.

Chapter titles and hours from the official syllabus ↗

Past questions and answers

1.Draw current time graph of alternating current.

2.Draw a time current graph of alternating current having frequency 2 Hz.

3.Write any two differences between direct current and alternating current.

4.Write any two ways of increasing electricity from dynamo. Figure: Diagram of an a.c. generator: rectangular coil rotating between N and S poles of two magnets, with slip rings, carbon brushes and terminals connected to load.

6.Write any two differences between electric motor and generator.

8.Draw a neat diagram of electric current production process by using a magnet and a coil.

9.Write one way to increase the magnitude of induced e.m.f. in a generator.

11.A transformer has 420 turns in primary coil and 70 turns in secondary coil. Calculate the secondary voltage if the primary voltage is 210 V.

12.A transformer has 6,000 turns in the primary coil and 1,000 turns in the secondary coil. Calculate the secondary voltage if the primary voltage is 210 V. (a) 25 V (b) 35 V (c) 45 V (d) 55 V

14.When a magnet is introduced into a coil, what happens to the needle of galvanometer. If the magnet is held at rest inside the coil, what will happen to the needle?

16.Under which one of the following principles does the transformer work? (a) Mutual Induction (b) Motor Effect (c) Electromagnetic Induction (d) Electromagnetic effect

18.Which of the current graph in the figure is applicable in functioning of a transformer? Explain with reason. Figure: Two current-versus-time graphs: Figure A shows a constant horizontal line (direct current); Figure B shows a sinusoidal wave (alternating current) against time t.

21.Which physical quantity always remains the same in a transformer? (i) Force (ii) Voltage (iii) Current (iv) Power

23.What is the major similarity in electric motor and current generator? (a) Both need AC input in their coil (b) Both need DC input in their coil (c) Coil of both is made of enamelled wire (d) Coil of both is made of non-enamelled wire

25.What amount of current can flow in the kettle written with 750 watt and 220 V? (a) 3 A (b) 3.4 A (c) 5 A (d) 7 A

26.Which one is the way to increase the magnitude of induced emf in a generator? (a) By increasing the length of magnet (b) By increasing the distance between the coil and the magnet. (c) By increasing the strength of magnetic field (d) By decreasing the speed of rotation

27.What will you do to increase the magnetic flux for the coil without changing the magnetic field of the bar magnet? Figure: A bar magnet (S on left, N on right) with magnetic field lines spreading out from the N pole toward a single-loop coil placed to the right of the magnet.

28.Write the unit of current electricity and pressure.

30.What is the frequency of DC? Why?

33.(i) When 240 V is passed in the primary coil of a transformer, 480 V is induced in secondary coil, if there are 300 turns in primary coil how many turns will be in secondary coil? (ii) Why is the core of a transformer laminated? (iii) Can transformer be used in DC circuit? Give reason.

34.Write the law of electromagnetic induction.

35.If number of primary turns is 300, calculate the number of turns in the secondary coil in the given figure. Figure: Transformer with a core, primary winding with input 220 V A.C. mains and secondary winding with output 44 V A.C.; primary turns = 300.

36.What is magnetic field?

38.When an alternating current of 60 Hz frequency is connected to the primary coil of a transformer, what will be the frequency of alternating current in the secondary coil?

39.If a current carrying conductor is placed in a permanent magnetic field, the conductor vibrates. What is such effect called? (a) Magnetic effect (b) Effect of Electromagnetic induction (c) Mutual Induction effect (d) Motor effect

40.The number of secondary coil is 10 times the primary coil in a transformer. If the transformer is connected to 230 V main line, how much secondary voltage is obtained? What type of transformer is this? Write a use of such transformer.

41.A transformer in a power house has 1:80 ratio of primary and secondary coils. If 400 V is passed into the primary coil what could be the voltage produced in the secondary coil? Can this transformer be used in domestic circuit?

42.Give one reason why wire vibrates when current/electricity is passed through the coil of the wire. Figure: A bar magnet (S on left, N on right) with an arrow pointing toward a coil of wire connected in a closed circuit with a galvanometer/bulb.

43.What type of transformer is shown in the figure? If the potential difference in A is 700 V, calculate the voltage produced in coil B. Figure: Transformer: primary coil A with n_p = 1000 turns, secondary coil B with n_s = 50 turns, on a common core.

44.Name an instrument in which electro-magnet is used, and write a use of that instrument.

47.Which type of energy conversion occurs in a generator? (a) Mechanical energy into electrical energy. (b) Magnetic energy into electrical energy. (c) Electrical energy into mechanical energy. (d) Magnetic energy into mechanical energy.

48.In a transformer the ratio of number of turns in primary coil and in secondary coil is 1:15. If such transformer is connected to 220 V power supply, calculate secondary voltage obtained from the transformer.

50.Which of the following is the source of Alternating current? (a) dry cell (b) solar panel (c) dynamo (d) voltaic cell

51.Identify a dependent variable in Ohm's law V=IRV=IRV=IR.

52.If a transformer has more turns in the secondary winding than in the primary winding, which of the following statements is correct? (a) It does not change A.C. voltage. (b) It decreases A.C. voltage. (c) It increases A.C. voltage. (d) It increases A.C. voltage according to the situation.

53.What is meant by 'the frequency of alternating current in our country is 50 Hz?

54.A charger has a transformer which reduces supply voltage from 220 V to 5 V. Calculate the ratio of number of turns in the primary coil to that of the secondary coil.

55.Based on which principle does the given device work? Figure: A bicycle wheel with a small dynamo (generator) mounted against the rim.

56.The number of turns in the secondary coil is 50 times more than that of primary coil. Calculate the output voltage, if 220 V input voltage is passed through this transformer. Which type of transformer is this? Where is such transformer used?

57.Which type of voltage is transformed by a transformer?

58.What is the electric device called that converts kinetic energy into electric energy?

59.What does an inverter do?

60.An electrical appliance is shown in the diagram. Figure: Transformer with primary coil of 100 turns at 220 V and secondary coil at 55 V. (a) On which principle is it based? (b) Calculate the number of turns in the secondary coil.

61.Nichrome wire is used in a heater. Why? Write any two reasons.

62.Inert gas is filled inside a filament lamp. Why? Write any two points.

63.Between a filament lamp and a CFL, which one helps to minimize load shedding and why?

68.What happen when bar magnet is placed inside solenoid at rest? Figure: A bar magnet (N and S poles marked) inside a solenoid whose ends are connected to a galvanometer.

69.Prove that electric resistance (Ω\OmegaΩ) =kg m2s−3A−2= kg\,m^2 s^{-3} A^{-2}=kgm2s−3A−2.

70.Prove that the unit of potential difference (V) = kg m2s−3A−1\text{kg m}^2\text{s}^{-3}\text{A}^{-1}kg m2s−3A−1

73.Lamp is lit in the running bicycle by the help of a dynamo but it goes off when bicycle is stopped. Give reason.

74.In domestic house hold wiring voltage of 220 V is supplied. A battery of mobile works with 3.7 V. Draw net diagram of transformer used in mobile charger.

75.A fan in a room rotates when its switch is made on. Which principle is used here?

76.Write an application of step up transformer and step-down transformer each.

77.What change occurs in output voltage if the number of turns in secondary coils is less than number of turns in primary coil? Write the reason.

78.If the load transmission at Dhalkebar, Dhanusha transmits electricity of 400 KV, then which type of transformer is used here? Also, draw figure showing primary (input) coil and secondary (output) coil in it.

Draw current time graph of alternating current.

Draw a time current graph of alternating current having frequency 2 Hz.

Write any two differences between direct current and alternating current.

Write any two ways of increasing electricity from dynamo.
Figure: Diagram of an a.c. generator: rectangular coil rotating between N and S poles of two magnets, with slip rings, carbon brushes and terminals connected to load.

Write any two differences between electric motor and generator.

Draw a neat diagram of electric current production process by using a magnet and a coil.

Write one way to increase the magnitude of induced e.m.f. in a generator.

A transformer has 420 turns in primary coil and 70 turns in secondary coil. Calculate the secondary voltage if the primary voltage is 210 V.

A transformer has 6,000 turns in the primary coil and 1,000 turns in the secondary coil. Calculate the secondary voltage if the primary voltage is 210 V.
(a) 25 V (b) 35 V (c) 45 V (d) 55 V

When a magnet is introduced into a coil, what happens to the needle of galvanometer. If the magnet is held at rest inside the coil, what will happen to the needle?

Under which one of the following principles does the transformer work?
(a) Mutual Induction (b) Motor Effect (c) Electromagnetic Induction (d) Electromagnetic effect

Which of the current graph in the figure is applicable in functioning of a transformer? Explain with reason.
Figure: Two current-versus-time graphs: Figure A shows a constant horizontal line (direct current); Figure B shows a sinusoidal wave (alternating current) against time t.

Which physical quantity always remains the same in a transformer?
(i) Force (ii) Voltage (iii) Current (iv) Power

What is the major similarity in electric motor and current generator?
(a) Both need AC input in their coil (b) Both need DC input in their coil (c) Coil of both is made of enamelled wire (d) Coil of both is made of non-enamelled wire

What amount of current can flow in the kettle written with 750 watt and 220 V?
(a) 3 A (b) 3.4 A (c) 5 A (d) 7 A

Which one is the way to increase the magnitude of induced emf in a generator?
(a) By increasing the length of magnet (b) By increasing the distance between the coil and the magnet. (c) By increasing the strength of magnetic field (d) By decreasing the speed of rotation

What will you do to increase the magnetic flux for the coil without changing the magnetic field of the bar magnet?
Figure: A bar magnet (S on left, N on right) with magnetic field lines spreading out from the N pole toward a single-loop coil placed to the right of the magnet.

Write the unit of current electricity and pressure.

What is the frequency of DC? Why?

(i) When 240 V is passed in the primary coil of a transformer, 480 V is induced in secondary coil, if there are 300 turns in primary coil how many turns will be in secondary coil?
(ii) Why is the core of a transformer laminated?
(iii) Can transformer be used in DC circuit? Give reason.

Write the law of electromagnetic induction.

If number of primary turns is 300, calculate the number of turns in the secondary coil in the given figure.
Figure: Transformer with a core, primary winding with input 220 V A.C. mains and secondary winding with output 44 V A.C.; primary turns = 300.

What is magnetic field?

When an alternating current of 60 Hz frequency is connected to the primary coil of a transformer, what will be the frequency of alternating current in the secondary coil?

If a current carrying conductor is placed in a permanent magnetic field, the conductor vibrates. What is such effect called?
(a) Magnetic effect (b) Effect of Electromagnetic induction (c) Mutual Induction effect (d) Motor effect

The number of secondary coil is 10 times the primary coil in a transformer. If the transformer is connected to 230 V main line, how much secondary voltage is obtained? What type of transformer is this? Write a use of such transformer.

A transformer in a power house has 1:80 ratio of primary and secondary coils. If 400 V is passed into the primary coil what could be the voltage produced in the secondary coil? Can this transformer be used in domestic circuit?

Give one reason why wire vibrates when current/electricity is passed through the coil of the wire.
Figure: A bar magnet (S on left, N on right) with an arrow pointing toward a coil of wire connected in a closed circuit with a galvanometer/bulb.

What type of transformer is shown in the figure? If the potential difference in A is 700 V, calculate the voltage produced in coil B.
Figure: Transformer: primary coil A with n_p = 1000 turns, secondary coil B with n_s = 50 turns, on a common core.

Name an instrument in which electro-magnet is used, and write a use of that instrument.

Which type of energy conversion occurs in a generator?
(a) Mechanical energy into electrical energy. (b) Magnetic energy into electrical energy. (c) Electrical energy into mechanical energy. (d) Magnetic energy into mechanical energy.

In a transformer the ratio of number of turns in primary coil and in secondary coil is 1:15. If such transformer is connected to 220 V power supply, calculate secondary voltage obtained from the transformer.

Which of the following is the source of Alternating current?
(a) dry cell (b) solar panel (c) dynamo (d) voltaic cell

Identify a dependent variable in Ohm's law $V=IR$ .

If a transformer has more turns in the secondary winding than in the primary winding, which of the following statements is correct?
(a) It does not change A.C. voltage. (b) It decreases A.C. voltage. (c) It increases A.C. voltage. (d) It increases A.C. voltage according to the situation.

What is meant by 'the frequency of alternating current in our country is 50 Hz?

A charger has a transformer which reduces supply voltage from 220 V to 5 V. Calculate the ratio of number of turns in the primary coil to that of the secondary coil.

Based on which principle does the given device work?
Figure: A bicycle wheel with a small dynamo (generator) mounted against the rim.

The number of turns in the secondary coil is 50 times more than that of primary coil. Calculate the output voltage, if 220 V input voltage is passed through this transformer. Which type of transformer is this? Where is such transformer used?

Which type of voltage is transformed by a transformer?

What is the electric device called that converts kinetic energy into electric energy?

What does an inverter do?

An electrical appliance is shown in the diagram.
Figure: Transformer with primary coil of 100 turns at 220 V and secondary coil at 55 V.
(a) On which principle is it based? (b) Calculate the number of turns in the secondary coil.

Nichrome wire is used in a heater. Why? Write any two reasons.

Inert gas is filled inside a filament lamp. Why? Write any two points.

Between a filament lamp and a CFL, which one helps to minimize load shedding and why?

What happen when bar magnet is placed inside solenoid at rest?
Figure: A bar magnet (N and S poles marked) inside a solenoid whose ends are connected to a galvanometer.

Prove that electric resistance ( $\Omega$ ) $= kg\,m^2 s^{-3} A^{-2}$ .

Prove that the unit of potential difference (V) = $\text{kg m}^2\text{s}^{-3}\text{A}^{-1}$

Lamp is lit in the running bicycle by the help of a dynamo but it goes off when bicycle is stopped. Give reason.

In domestic house hold wiring voltage of 220 V is supplied. A battery of mobile works with 3.7 V. Draw net diagram of transformer used in mobile charger.

A fan in a room rotates when its switch is made on. Which principle is used here?

Write an application of step up transformer and step-down transformer each.

What change occurs in output voltage if the number of turns in secondary coils is less than number of turns in primary coil? Write the reason.

If the load transmission at Dhalkebar, Dhanusha transmits electricity of 400 KV, then which type of transformer is used here? Also, draw figure showing primary (input) coil and secondary (output) coil in it.