Answer the questions.[Phy-2M]

Question 12 Marks

Calculate the cost of seeing 2 movies on colour T.V. daily for the month of September.
Given wattage of colour T.V. $=60 \mathrm{~W}$, duration each movie is 2 hours 30 min and 1 kWh costs Rs. 4

Answer

Wattage of colour T.V. $=60 \mathrm{~W}$
Number of hours for which colour T.V. is on during September $=2 \times 2 \frac{1}{2} \times 30=150 \mathrm{~h}$
Energy consumed $=\frac{\text { watt } \times \text { hour }}{1000}=\frac{60 \times 150}{1000}=9 \mathrm{kWh}$
Cost of seeing 2 movies per day for 30 days $=9 \times 4=$ Rs. 36 only.

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Question 22 Marks

A potential difference of 220 V is applied across a resistance of $440 \Omega$ in an electric ion.
(i) Find the current.
(ii) Heat energy produced is 30 s .

Answer

Here $\mathrm{V}=220$ volts; $\mathrm{R}=440 \Omega$Now $I=\frac{V}{R}=\frac{220}{440}=0.5 \mathrm{~A}$
Heat energy produced in 30s $=\frac{V^{2}}{R} T=\frac{(220)^{2} \times 30}{440}=3300 \mathrm{~J}$

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Question 32 Marks

Name the factors on which brightness of image in a camera depends and how?

Answer

The brightness of the image in the camera is:
a. directly proportional to time of exposure(t).
b. directly proportional to the square of diameter of aperture of the lens system (i.e. light gathering power of the objective).
c. inversely proportional to the square of focal length of the lens system.
d. is inversely proportional to the square of the lateral magnification. i.e. Image Brightness $\propto\left(N_{A} / M\right)^{2}$; where $\mathbf{N}_{\mathbf{A}}$ is the objective numerical aperture and $\mathbf{M}$ is the magnification.

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Science Answer the questions.[Phy-2M]

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