Question

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

Answer 1

Answer:

2.50 x 10⁻⁶ N.

Explanation:

Energy flux = 25 × 10⁴ Wm⁻²

Surface area = 15 cm²

Average force = Δp\Δt

Light falls on a perfectly reflecting surface at normal incidence.

Since the surface is perfectly reflecting, thus - Δp = 2Δt/c

F = 2 × [ΔE/cΔt]

F = 2 ×p/c

F = 2 x (25 x 10 x 15 x 10) / ( 3 x 10⁸)

F = 2.5 x 10⁻⁶  N

Therefore, the average force exerted on the surface is  2.50 x 10⁻⁶ N.