Solve this: Question No 13 A pulse of light of duration 100 ns is absorbed completely by a small - Physics - Magnetism And Matter

Question

Solve this:
Question No 13
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 × 10 8 m/s The final momentum of the
object is
A 0 3 × 10 - 17   k g   m s - 1
B 1 0 × 10 - 17   k g   m s - 1
C 3 0 × 10 - 17   k g   m s - 1
D 9 0 × 10 - 17   k g   m s - 1

Pintu B. · Accepted Answer

Dear Student ,
Since the light pulse is completely absorbed by the
object, the entire momentum of the pulse is transferred to the
object If E is the energy of the pulse, the momentum
p is given by
p = E/c where c is the speed of light in free
space
But E = Pt where P is the power
and t is the duration of the pulse
Therefore, we have
p = Pt/c = (30×10–3)×(100×10–9) /( 3×108) = 1×10–17 kg
ms–1

Regards