4.20 A magnetic field set up using Helmholtz coils (described in Exercise 4.16) is uniform in a small region and has a magnitude of 0.75 T. In the same region, a uniform electrostatic field is maintained in a direction normal to the common axis of the coils. A narrow beam of (single species) charged particles all accelerated through 15 kV
enters this region in a direction perpendicular to both the axis of the coils and the electrostatic field. If the beam remains undeflected when the electrostatic field is , make a simple guess as to what the beam contains. Why is the answer not unique?
Let the beam consist of particles having charge q and mass m.
After being accelerated through a potential difference V its velocity can be found out by using the following relation,
Using the value of v from equation (ii) in (i) we have