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:(a) 1.25 × 10⁻⁶ N(b) 2.50 × 10⁻⁶ N(c) 1.20 × 10⁻⁶ N(d) 3.0 × 10⁻⁶ N

Answer 1

For this question option D

Answer 2

Answer:

B) 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.