Dual Nature Of Matter Question 8
Question 8 - 30 January - Shift 1
A point source of light is placed at the centre of curvature of a hemispherical surface. The source emits a power of $24 W$ The radius of curvature of hemisphere is $10 cm$ and the inner surface is completely reflecting. The force on the hemisphere due to the light falling on it is $\times 10^{-8} N$.
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Answer: (4)
Solution:
Formula: Force due to radiation
$ p_0=24 W $
Force $=\int PdA \cos \theta$
$=\frac{2 I}{C} \int dA \cos \theta=\frac{2 I}{C} \pi R^{2}=2 \frac{p_0}{4 \pi R^{2}} \cdot \frac{\pi R^{2}}{C}$
$=\frac{p_0}{2 C}=\frac{24}{2 \times 3 \times 10^{8}}=4 \times 10^{-8} N$ (Ans)
