Question

# Light is incident normally on a completely absorbing surface with an energy flux of $$25 W cm^{-2}$$.  if the surface has an area of $$25 cm^{-2}$$, the momentum transferred to the surface in 40 min time duration will be :

A
5.0×103Ns
B
3.5×106Ns
C
1.4×106Ns
D
6.3×104Ns

Solution

## The correct option is D $$5.0 \times 10^{-3} Ns$$Pressure = $$\dfrac{I}{C}$$Force = Pressure $$\times$$ Area = $$\dfrac{I}{C}$$. AreaMomentum transferred = Force . $$\Delta t$$$$= \dfrac{I}{C} .$$ Area .$$\Delta t$$$$= \dfrac{25 \times 10^4}{3 \times 10^8} \times 25 \times 10^{-4} \times 40 \times 60$$$$\rightarrow 5 \times 10^{-3} N-s$$Physics

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