Light with an energy flux of 18W/cm2 falls on a non-reflecting surface at normal incidence If the surface has - Physics - Nuclei

Question

Light with an energy flux of 18W/cm2 falls on a
non-reflecting surface at normal incidence If the surface has an
area of 20cm2, find the average force exerted on the
surface during a 30 min time span

Vijay Yadav · Accepted Answer

Average force by light on surface is given by $F_{a v} = \frac{Δ P}{Δ t}$

Δt = 30 min

= 30 × 60s

= 1800s

ΔP = Change in momentum

$= P_{f} - P_{i} P_{f} = 0 P_{i} = \frac{E}{C} Hence F_{a v} = - \frac{E}{C . Δ t}$

Given that intensity of light $I = \frac{18 W}{{cm}^{2}}$

Total power absorbed by surface = I × area of surface

= (18 W/cm²) (20 cm²)

= 360 W

$So, F_{a v} = - \frac{E}{C . Δ t} = - \frac{P ower}{C} = - \frac{360}{3 \times 10^{+ 8}} = - 120 \times 10^{- 8} N F_{a v} = - 1.2 \times 10^{- 6} N$

Average force by the surface = 1.2 × 10^–6 N

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Light with an energy flux of 18W/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 20cm2, find the average force exerted on the surface during a 30 min time span.

Light with an energy flux of 18W/cm² falls on a non-reflecting surface at normal incidence. If the surface has an area of 20cm², find the average force exerted on the surface during a 30 min time span.