What are the magnitude and direction of the field in which the proton moves?

Question

Looking down on its path, a 1 MeV- proton travels clockwise with a radius of 10cm. What are the magnitude and direction of the field in which the proton moves?

Answer 1

If a charge moves into a magnetic field with direction perpendicular to the field, it will follow a circular path. The magnetic force, being perpendicular to the velocity, provides the centripetal force.

r=mv/qB

solving for B

B = mv/qr

1 eV = 1.6 x 10^-19 Joules

1 Mev = 1.6 x 10^-13 joules

Solve for B; using mass of proton and charge of proton and r in meters and calculating v from its KE.

Use Right Hand Rule to find direction of motion of proton.

If v is toward the top of the page and F=q(v X B) is to the right,  (CW), then B must be up out of the page.