Question

Two charges of same magnitude move in two circles of radii R1=R and R2=2R in a region of constant uniform magnetic field B0<br />the work W1and W2 done by magnetic field in two cases respectively are such that :<br />A:W1=W2=0<br />B:W1>W2<br />C:W1=W2 is not equal to 0<br />D:W1<W2

Answer 1

In the presence of magnetic field, a moving charge experiences centripetal force given as  FB = qvBsin,which acts perpendicular to the velocity vector v.

Since the trajectory of such charge particle is circular, at any instant velocity vector acts along the tangent to the circle.

FB is perpendicualr to v.

So work done by magnetic Lorentz force FB  (due to B) will always be zero.

 

So correct option is (a) W1 = W2 = 0

 I hope that clarifies your query