CBSE Class 12-science Answered

As the speed of the ions increases, its mass also increases according to the relation-

Where m₀ = the rest mass of the ion

m = the mass of ion while moving with velocity

c = velocity of light.

 Now, the time taken by the ion to describe semicircular path is given by

It shows that as v increases, t increases. It means that the positive ion will take longer time to describe semicircular path than the time for half cycle of oscillating electric field. As a result, the ion will not arrive in the gap between the two dees exactly at the instant; the polarity of the two dees is reversed and hence will not be accelerated further.