0

Guest

Courses New

A parallel beam of monochromatic light of wavelength 500 nm is incident normally on a perfectly absorbing surface. The power through any cross–section of the beam is 10 W. Find (a) the number of photons absorbed per second by the surface and (b) the force exerted by the light beam on the surface.

A parallel beam of monochromatic light of wavelength 500 nm is incident normally on a perfectly
absorbing surface. The power through any cross–section of the beam is 10 W. Find (a) the number of photons absorbed per second by the surface and
(b) the force exerted by the light beam on the surface.

Grade:12

1 Answers

Arun
25750 Points
6 years ago
(a) Energy of each photon is
E = hc / \lambda 
 = 1242 eV – nm/ 500 nm
 = 2.48 eV
In one second 10 J energy passes through any cross section of the beam,
Thus the no. of photons crossing a cross section is = 
 n = 10 J / 2.48 eV
n = 2.52 * 1019
 
(b)
total momentum of all the photons = 
 p = nh/ \lambda = nh \nu/ c = 10 J / 3*108
 = 3.33 * 10 –8 N-sec
 
hence total force F = dP/dt = 3.33 *10 –8 Newton

Think You Can Provide A Better Answer ?

Other Related Questions on Wave Optics

View all Questions »

ASK QUESTION

Get your questions answered by the expert for free

Answer and earn gift vouchers

Win Gift vouchers upto Rs 500/-

View courses by askIITians

Design classes One-on-One in your own way with Top IITians/Medical Professionals

Click Here Know More

Complete Self Study Package designed by Industry Leading Experts

Click Here Know More

Live 1-1 coding classes to unleash the Creator in your Child

Click Here Know More

a Complete All-in-One Study package Fully Loaded inside a Tablet!

Click Here Know More