(D) For a perfectly reflecting surface,the radiation force $F$ exerted by a beam of power $P$ is given by $F = \frac{2P}{c}$,where $c$ is the speed of

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(D) For a perfectly reflecting surface,the radiation force $F$ exerted by a beam of power $P$ is given by $F = \frac{2P}{c}$,where $c$ is the speed of light.For the disc to levitate,this radiation force must balance the gravitational force (weight) acting on the disc: $F = mg$.Equating the two,we get $\frac{2P}{c} = mg$.Given: $P = 1.5 \,kW = 1.5 \times 10^3 \,W$,$c = 3 \times 10^8 \,m/s$,and taking $g = 10 \,m/s^2$.Substituting the values: $\frac{2 \times 1.5 \times 10^3}{3 \times 10^8} = m \times 10$.$\frac{3 \times 10^3}{3 \times 10^8} = 10m$.$10^{-5} = 10m$.$m = 10^{-6} \,kg$.

Class 12 Physics Dual Nature of Radiation and matter Radiation Force and Pressure

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$A$ $1.5 \,kW$ laser beam of wavelength $6400 \,\mathring A$ is used to levitate a thin aluminium disc of the same area as the cross-section of the beam. The laser light is reflected by the aluminium disc without any absorption. The mass of the foil is close to ......... $kg$.

KVPY 2014 All KVPY

A
$10^{-9}$
B
$10^{-3}$
C
$10^{-4}$
D
$10^{-6}$

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Dual Nature of Radiation and matter

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Radiation Force and Pressure

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MediumKCET 2018

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$A$ $1.5 \,kW$ laser beam of wavelength $6400 \,\mathring A$ is used to levitate a thin aluminium disc of the same area as the cross-section of the beam. The laser light is reflected by the aluminium disc without any absorption. The mass of the foil is close to ......... $kg$.

Similar Questions

An astronaut floating freely in space decides to use his flashlight as a rocket. He shines a $10$ $W$ light beam in a fixed direction so that he acquires momentum in the opposite direction. If his mass is $80$ kg,how long must he shine the light to reach a velocity of $1$ $m/s$?

$A$ pulse of light of duration $100 \ ns$ is absorbed completely by a small object initially at rest. The power of the pulse is $30 \ mW$ and the speed of light is $3 \times 10^8 \ m/s$. The final momentum of the object is:

$A$ plate of mass $10 \text{ g}$ is in equilibrium in air due to the force exerted by a light beam on the plate. Calculate the power of the beam,if the plate is perfectly absorbing.

$50\, W/m^2$ energy density of sunlight is normally incident on the surface of a solar panel. Some part of incident energy $(25\%)$ is reflected from the surface and the rest is absorbed. The force exerted on $1\, m^2$ surface area will be close to $(c = 3 \times 10^8\, m/s)$.

The number of photons falling per second on a completely darkened plate to produce a force of $6.62 \times 10^{-5} \ N$ is $n$. If the wavelength of the light falling is $5 \times 10^{-7} \ m$,then $n = \_ \times 10^{22}$. (Given: $h = 6.62 \times 10^{-34} \ J \cdot s$)

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