First slide

Momentum and Radiation pressure

Question

A radiation of energy ‘E’ falls normally on a perfectly reflecting surface. The momentum transferred to the surface is (C = Velocity of light )

Moderate

A

$\frac{2 E}{C^{2}}$
B

$\frac{E}{C^{2}}$
C

$\frac{E}{C}$
D

$\frac{2 E}{C}$

Solution

$Energy of radiation, E = h v = \frac{h C}{λ}$
$Also, its momentum p = \frac{h}{λ} = \frac{E}{C} = p_{i}$
$p_{r} = - p_{i} = - \frac{E}{C}$
So, momentum transferred to the surface
$= p_{i} - p_{r} = \frac{E}{C} - (- \frac{E}{C}) = \frac{2 E}{C}$

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