An alpha particle travels in the x-direction with a velocity of 10^3 m/s. It enters a region with an electric?

Question

An alpha particle travels in the x-direction with a velocity of 10^3 m/s. It enters a region with an electric field in the y-direction, of 50 N/C.

a. What are the magnitude and direction of a magnetic field such that the particle comes undeflected?

b. Replace the alpha-particle by an electron and repeat.

Answer 1

a)

q(vXB) =qE

B = E/v=50x10^-3 Tesla in the +z direction

b)

Since v= E/B when the forces of E and B are equal

B must be the same value but pointing in the opposite direction , that is -z, because of the negative sign of the charge.