Solveeit Logo
Login

Question

Physics Question on Electromagnetic waves

Light with an energy flux of 25×104Wm−225 \times 10^4 W m^{-2} falls on a perfectly reflecting surface at normal incidence. If the surface area is 15cm215 c m^2, the average force exerted on the surface is

A

1.25×10−6N1.25 \times 10^{-6} N

B

2.50×10−6N2.50\times10^{-6} N

C

1.20×10−6N1.20\times10^{-6}N

D

3.0×10−6N3.0\times10^{-6}N

Answer

2.50×10−6N2.50\times10^{-6} N

Explanation

Solution

Here,
Energy flux, I=25×104Wm−2I= 25 \times {10}^4 W m^{-2}
Area, A=15cm2=15×10−4m2A = 15 c m^2 = 15 \times {10} ^{-4} m^2
Speed of light, c=3×108ms−1 c= 3 \times {10}^8 m s^{-1}
For a perfectly reflecting surface, the average force exerted on the surface is
F=2IAc=2×25×104Wm−2×15×10−4m23×108 m s−1F= \frac{ 2IA}{ c} = \frac{ 2 \times 25 \times 10^{4} W m^{-2} \times 15 \times 10^{-4} m^{2} }{ 3 \times 10^{8} \,m\, s^{-1}}
=250×10−8N=2.50×10−6 N= 250 \times {10}^{-8} N = 2.50 \times {10}^{-6} \,N