A magnetic field, set up using Helmhotlz coils, is uniform, in a small region and has a magnitude of `0.75t`. 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 (sinle species) charged particles, all accelerated through 15KV, enters this region in direction perpendicular to both the axis of the coils and the electrostatic field. if the beam remains undeflected when the electrostatic field is `9.0xx10^(5)V*m^(-1)`, make a simple guess as to what the beam contains. Why is the answer not unique ?

Explanation

`B=0.75 T, E=9xx10^(5)Vm^(-1)`
`V=(E )/(B)=(9xx10^(5))/(0.75)=12xx10^(6) m//s`
K.E of charged particle
`=(1)/(2) mV^(2)=eV`
or `(e )/(m)=(v^(2))/(2V)=(144xx10^(12))/(2xx15000)=4.8xx10^(7)C kg^(-1)`
Particle is deuteron, the answer is not unique because only the ratio fo charge to mass is determined. Other possibe answer are `He^(++), Li^(+++)` etc.
`therefore He^(++) and Li^(+++)` also have the same value of
`e//m(because e//m=(2e)/(2m)=(3e)/(3m))`