Question

20.
Electromagnetic wave of intensity 1400 W/m² falls
on metal surface on area 1.5 m² is completely
absorbed by it. Find out force exerted by beam.
(1) 14 x 10-5 N (2) 14 x 10-6 N
(3) 7 x 10-5 N
(4) 7 x 10-6 N​

Answer 1

Answer:

(4) 7 * 10^-6 N

Explanation:

For a perfectly absorbing surface

F = IA/c

= (1400 W/m^2 * 1.5 m^2)/(3 * 10^8 m/s)

= 7 * 10^-6 N

Answer 2

The force exerted by the beam is $7\times 10^{-6}\ N$.

Explanation:

It is given that,

Intensity of the electromagnetic wave, $I=1400\ W/m^2$

Area of the surface, $A=1.5\ m^2$

For a perfectly absorbing surface, the force exerted by the beam is given by :

$F=\dfrac{IA}{c}$

c is the speed of light

$F=\dfrac{1400\times 1.5}{3\times 10^8}$

$F=7\times 10^{-6}\ N$

So, the force exerted by the beam is $7\times 10^{-6}\ N$. Hence, this is the required solution.

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