Question

What happens when a photon moving with a speed 3 × 10⁸ m/s enters perpendicular to a uniform magnetic field B?
1. The photons traces a circular path in the magnetic field
2. The photon moves un-deviated in the magnetic field
3. The speed of photon decreases
4. The photon will get pulled out of the magnetic field

Answer 1

Correct Answer - Option 2 : The photon moves un-deviated in the magnetic field

The correct answer is option 2) i.e. The photon moves un-deviated in the magnetic field

CONCEPT:

• Lorentz force: A charged particle moving relative to a magnetic field experiences a force due to the magnetic field. This force is called the Lorentz force.
  • When a charged particle q is moving with a velocity of v in a magnetic field of intensity B, the Lorentz force (F) is given by:

F = q(v × B)

• The direction of force is found by the right-hand rule - Curl the fingers of the right hand as if rotating vector v into vector B.
  • The direction of the thumb gives the direction of the Lorentz force.

EXPLANATION:

• A photon has no electrical charge. 

⇒ q = 0

• The Lorentz force experienced by the photon, F = q(v × B) = 0(v × B) = 0.
• Thus, the photon experiences zero force i.e. it goes un-deviated in the magnetic field.