Question

When the radiation coming out from certain radioactive substance is passed through an electric field marks are found at three place on the photographic plate placed in path.

Answer 1

Because the radiation coming from the nuclear substance consists of
alpha rays
beta rays
and gamma rays
alpha rays are positively charged therefore they deflect towards the negatively charged Cathode..
Beta rays are negatively charged and therefore moves towards the positively charged anode.
And Gamma rays are electrically neutral therefore they are not deflected by the electric field..
Therefore a single ray coming from the nuclear substance gets divided into three rays and
strike the photographic plate at three places..
hope it helps u..

Answer 2

because the radiation coming from the nuclear substance consists of alpha rays beta rays and gamma rays alpha rays are positively charged therefore they deflect toward the negatively charged cathode.