Question

Light with an energy flux of 25×104wm−2 falls on a perfectly reflecting surface at normal incidence. If the surface area is 15cm2 , the average force exerted on the surface is:

Answer 1

Answer:

Explanation:

=> It is given that,

energy flux = 25 * $10^{4}$ wm^-2

Surface area = 15 cm^{2}

=> For the Average force extend on the surface = Δp /Δt

=> Here, Light falls on a perfectly reflecting surface at normal incidence.

∴ Δp = 2Δt/c

F = 2*[ΔE/cΔt]

  = 2*p/c

$=2\:.\:\frac{25 \times 10 \times 15 \times 10}{3 \times 10^8}N$

  = 2.5 x $10^{-6}$ N

Therefore, the average force exerted on the surface is  2.5 x $10^{-6}$ N.

Answer 2

F= 2IA/C

2(25×10^-4×15×10^-4)/3×10^8

= 2.50×10^6N