Moving Charges and Magnetism - Result Question 25
25. A charge moving with velocity v in $X$-direction is subjected to a field of magnetic induction in negative $X$-direction. As a result, the charge will
(a) remain unaffected
[1993]
(b) start moving in a circular path $Y-Z$ plane
(c) retard along $X$-axis
(d) move along a helical path around $X$-axis
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Answer:
Correct Answer: 25. (a)
Solution:
- (a) The force acting on a charged particle in magnetic field is given by
$\vec{F}=q(\vec{v} \times \vec{B})$ or $F=q v B \sin \theta$,
When angle between $v$ and $B$ is $180^{\circ}$,
$F=0$
Force, $\vec{F}=\vec{q}(\vec{v} \times \vec{B})=q v B \sin \theta$ When $\theta=0^{\circ}, 180^{\circ}$ then particle will be moving in a direction parallel or antiparallel to the field. In such cases, the trajectory of the particle is a straight line.
