Question 22: EM waves

Question

A pulse of light of duration 100 ns is absorbed completely by a small object initially at rest. Power of the pulse is 30 mW and the speed of light is 3 $$	imes$$ 108 ms$$-$$1. The final momentum of the object is

Accepted Answer

Duration of pulse, t = 100 ns = 100 $$	imes$$ 10
$$-$$9
s.
Power of the pulse, P = 30 mW = 30 $$	imes$$ 10
$$-$$3
W.
Speed of light, c = 3 $$	imes$$ 10
8
ms
$$-$$1
The final momentum of the object is
$$p = {E \over c} = {{P 	imes t} \over c} = {{30 	imes {{10}^{ - 3}} 	imes 100 	imes {{10}^{ - 9}}} \over {3 	imes {{10}^8}}} = {10^{ - 17}}$$ kg-ms
$$-$$1

Answer

0.3 $$	imes$$ 10$$-$$17 kg-ms$$-$$1

Answer

1.0 $$	imes$$ 10$$-$$17 kg-ms$$-$$1

Answer

3.0 $$	imes$$ 10$$-$$17 kg-ms$$-$$1

Answer

9.0 $$	imes$$ 10$$-$$17 kg-ms$$-$$1

EM waves

A pulse of light of duration 100 ns is absorbed completely by a small object initially at rest. Power of the pulse is 30 mW and the speed of light is 3 $\times 108 ms-$1. The final momentum of the object is

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