Question

Which one of the following statements about photon is incorrect?
1. Photon's rest mass is zero
2. Momentum of photon is hv/c
3. Photon's energy is hv
4. Photon exerts no pressure

Answer 1

Correct Answer - Option 4 : Photon exerts no pressure

CONCEPT:

• The photoelectric effect led to the conclusion that light is made up of a quantum of energy. Einstein through his experiments predicted that quanta of light have momentum which indicated the particle nature of light. This particle nature of light is called photons 
• The properties of a photon are 
  • Photon is an elementary particle 
  • Irrespective of the frequency of radiation the momentum and energy of the photons remains constant for each photon
  • Photons are electrically neutral 
  • The rest mass of the photon is zero and is electrically neutral

EXPLANATION:

• The pressure exerted by an electromagnetic wave is given by

\(\Rightarrow P = \frac{U}{C}\)

Where U = intensity of the wave, and C = Velocity of light

• The velocity of a photon is equal to the velocity of light, hence according to the above equation the photon must exert pressure on the surface 
• Option 4 is the wrong statement.