Question

A positive charge 'q' of mass 'm' is moving along the +x axis with speed v. We wish to apply a
uniform magnetic field B for time At so that the charge reverse its direction crossing the y axis at
a distance d. Then what is B and time​

Answer 1

Explanation:

To change the direction of charge, a force needs to be applied such that,

qvB=

r

mv

2

where r=d/2

Therefore,

B=

qd

2mv

Total displacement is d when charge travels for time, δt

Therefore,

δt=

2v

πd