Answer the questions.[Phy-2M]

Question 12 Marks

a. Write the mathematical expression for Joule's law of heating.
b. Compute the heat generated while transferring 96000 coulomb of charge in two hours through a potential difference of 40 V .

Answer

a. The mathematical expression of the Joules Law of heating is: $H=I^{2} R t$Here, H is a heating effect, I is the current flowing through the device and t is the time taken.
b. Given:
Amount of charge transferred $=96000 \mathrm{C}$
Time taken $=2 \mathrm{hrs}=2 \times 60 \times 60 \mathrm{sec}=7200 \mathrm{sec}$
Potential difference $=40 \mathrm{~V}$
Heat generated $=\mathrm{V} \times \mathrm{I} \times \mathrm{t}$
and we know that; $\mathrm{I}=\frac{Q}{t}$
So, H = VQ
$=40 \times 96000$
$=3.84 \times 10^{6} \mathrm{~J}$

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Question 22 Marks

Calculate the equivalent resistance of the following electric circuit:

Answer

$ R _{ S }= R _3+ R _4=10+10=20 \Omega $
$\frac{1}{R_p}=\frac{1}{R_2}+\frac{1}{R_S} $
$=\frac{1}{20}+\frac{1}{20}=\frac{1}{10} \Omega $
$R _{ p }=10 \Omega$
$\text { Total equivalent resistance }= R = R _1+ R _{ p }+ R _5 $
$= R = 2 0 + 1 0 + 1 0 = 4 0 \Omega$

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Question 32 Marks

State Snell's law of refraction of light. Write an expression for the absolute refractive index of a medium in terms of speed of light.

Answer

Statement of Snell's Law: The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of media.
If $i$ is the angle of incidence and $r$ is the angle of refraction, then.
$\frac{\sin i}{\sin r}=$ constant
- Absolute Refractive Index of a medium $=\frac{\text { Speed of Light in vacuum }}{\text { Speed of Light in the medium }}$

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