A particle having a charge`20mu C` and mass `20mug` moves along a circle of radius 5.0 cm under the action of a magnetic field B = 1.0 T. When the particle is at a point P, a uniform electric field is switched on and it is found that the particle continues on the tangent through P with a uniform velocity. Find the electric field.

Explanation

When the particle moves along a circle in the magnetic
field B, the magnetic force is redially inward. If an
electric field of proper magnitude is switeched on which
is directed radially outwards, the particle may
experience no force. It will then move along a straight
line with uniform velocity. This will be the case when
`qE = qvB or, E = vB.`
The radius of the circle in a magnetic field is given by
`r = (mv)/(qB)`
or, `v=(rqB)/(m)`
`=(5.0X10^(-2)m)(20X10^(-6) C)(1.0T)/(20X10^(-9)kg) =50m s^(-1)`
The required electric field is
`E = vB = (50 ms^(-1))(1.0T)`
`= 50 V m ^(-1)`
This field will be in a direction whic is radially outward
at `P`.