MCQ
If a charged particle at rest experiences no electromagnetic force:
- AThe electric field must be zero.
- BThe magnetic field must be zero.
- CThe electric field may or may not be zero.
- DThe magnetic field may or may not be zero.
✓
Answer
- The electric field must be zero.
- The magnetic field may or may not be zero.
Explanation:
Force on charged particle in an electric eld, $\text{F} = \text{qE} \ ...(1)$
Force on charged particle in a magnetic eld $\text{F} = \text{q} (\text{v}\times\text{b}) = \text{qvB} \sin\theta \ ...(2) $
Where boldface letter represent vector nature of that quantity, q is charge of the particle, v is the velocity of the particle( if any), and $\theta$ is the angle between velocity and magnetic eld.
From (1), FE = 0 only when either q = 0 or E = 0.
Let q ≠ 0, and F ≠ 0, then we must have E ≠ 0
From (2), if q ≠ 0, v ≠ 0 and B ≠ 0 even then FB can be 'zero' because of θ = 0° or 180°
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