Question

Identify in which of the following cases would the charge experience a magnetic force?
I. The stationary charge is placed inside the magnetic field
II. The charge is moving and its velocity is perpendicular to the magnetic field lines
III. The charge is moving and its velocity is parallel to the magnetic field lines

• A. I only
• B. I and II only
• C. II and III only
• D. II only
• E. III only

Answer 1

Answer: (D)

II only

Magnetic force $F=qvB$ $sin\theta$ where $\theta$ is the angle between $v$ and $B$

$I$ : $v=0$ $⟹F=0$

$II$ : $\theta ={90}^0$ $⟹F=qvB$ $\times sin{90}^o=qvB$

$III$ : $\theta =0^0$ $⟹F=qvB$ $\times sin{0}^o=0$

Hence option D is correct.