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A 1100 \mathrm{~W} light bulb is placed at the centre of a spherical chamber of radius 20 \mathrm{~cm}. Assume that 60 \%  the energy supplied to the bulb is converted into light and that the surface of the chamber is perfectly absorbing. The force and pressure exerted by the light on the surface of chamber is:
 

Option: 1

3.6 \times 10^{-6} \mathrm{~N}, 4.4 \times 10^{-6} \mathrm{~N} / \mathrm{m}^2


Option: 2

\quad 7.3 \times 10^{-6} \mathrm{~N}, 8.8 \times 10^{-6} \mathrm{~N} / \mathrm{m}^2


Option: 3

3.6 \times 10^{-6} \mathrm{~N}, 8.8 \times 10^{-6} \mathrm{~N} / \mathrm{m}^2


Option: 4

7.3 \times 10^{-6} \mathrm{~N}, 4.4 \times 10^{-6} \mathrm{~N} / \mathrm{m}^2


Answers (1)

best_answer

Consider a spherical chamber of radius 20\mathrm{~ cm}.
Bulb is placed at point s as shown in figure.

Intensity of light at surface, I=\frac{0.6 \mathrm{P}}{4 \mathrm{r}^2}

Force, exerted on the surface, F=\frac{P}{c}

Where P is power of bulb.

\therefore \mathrm{F}=\frac{1100}{3 \times 10^8}=3.6 \times 10^{-6} \mathrm{~N}

Pressure exerted by light, \mathrm{P}=\frac{\mathrm{I}}{\mathrm{c}}=\frac{0.6 \mathrm{P}}{4 \pi \mathrm{r}^2 \mathrm{c}}=\frac{0.6 \times 1100}{4 \pi(0.2)^2 \times 3 \times 10^8}=4.4 \times 10^{-6} \mathrm{~N} / \mathrm{m}^2

Posted by

Divya Prakash Singh

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