Basic Physics for Telecommunications

(a) [LT⁻²]

Gravitational intensity (field strength) is force per unit mass: (g = F/m), so its unit is N/kg = m/s², giving the dimension formula ([LT^{-2}]).

(a) Watt per meter square

Radiation power density is the power radiated per unit area, so its SI unit is watt per square metre (W/m²).

Archimedes's Principle

Statement: When a body is wholly or partly immersed in a fluid at rest, it experiences an upward thrust (buoyant force) equal to the weight of the fluid displaced by the body.

Explanation: When a body is dipped in a liquid, the liquid exerts pressure on all sides of the body. Since pressure increases with depth, the upward pressure on the bottom surface is greater than the downward pressure on the top surface. This difference of pressure produces a net upward force called the upward thrust or buoyant force.

If a body of volume $V$ is fully immersed in a liquid of density $\rho$, then:

$F_B = V\rho g = W_{\text{displaced liquid}}$

Conditions:

• If weight of body $>$ buoyant force → body sinks.
• If weight of body $=$ buoyant force → body floats wholly immersed.
• If weight of body $<$ buoyant force → body floats partly immersed.

Applications: Ships and boats floating on water, hydrometer, submarine, hot-air balloon, and lactometer.

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Difference between Density and Specific Gravity

Relation: $\text{Density} = \text{Specific gravity} \times \text{density of water}$