Question

Light is incident normally on a completely reflecting surface with an intensity of 100W/.If the surface has an area of 100c, the momentum transferred to the surface in 20 min time duration is--------SI units

Answer 1

Light is incident normally on a completely reflecting surface with an intensity of 100W/cc.If the surface has an area of 100cc, the momentum transferred to the surface in 20 min time duration is 4 × 10⁻³ kg-m/s in SI units.

Explanation:

Incident light intensity I = 100 W/cc

Area of cross section A = 100 cc

duration t = 20 min = 1200 seconds

Therefore, the incident energy

$E=IAt$

$\implies E=100\times 100\times 1200$

$\implies E=1.2\times 10^6$ Joule

Incident momentum

$p=\frac{E}{c}$

$\implies p=\frac{1.2\times 10^6}{3\times 10^8}$

$\implies p=0.4\times 10^{-2}$

$\implies p=4\times 10^{-3}$ kg-m/s

Hope this answer is helpful.

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