Question

A beam of protons is deflected sideways. Could this deflection be caused
(1) By an electric field ?
(2) By a magnetic field ?
(3) If either could be responsible how would you be able to tell which was present ?

Answer 1

(1) yes
(2) yes
(3) On reversing the direction of the projection of protons, if the protons are deflected in the same direction, then the deflection is due to electric field, if the protons are deflected in the opposite direction, then the deflection is due to magnetic field