Concepts Of Physics MCQ Edition [Volume 2]PhysicsPhotoelectric Effect and Wave–Particle Duality
A parallel beam of monochromatic light having a wavelength of 663 nm is incident on a totally reflecting plane mirror. The angle of incidence is 60^ , and 1.0 10¹⁹ photons strike the mirror each second. Determine the force exerted by the light beam on the mirror.
Options
- A1.73 10⁻⁸ N
- B1.0 10⁻⁸ N
- C2.0 10⁻⁸ N
- D5.0 10⁻⁹ N
Correct answer
B. 1.0 10⁻⁸ N
Step-by-step solution
The momentum of a single photon is given by p = h . When a photon strikes a totally reflecting mirror at an angle of incidence , the component of its momentum perpendicular to the mirror is p . Upon reflection, this perpendicular component reverses its direction, while the parallel component remains unchanged. The change in momentum of each photon is: p = 2p = 2h The force exerted on the mirror is the total change in momentum per second, which is the product of the number of photons striking per second ( n ) and th