Question

A proton is moving in the +z direction when it enters a uniform magnetic field in the -x direction. What is the direction of the initial force on the proton?

Answer 1

Magnetic force is given by:

F = q*VxB

F = q*V*B*sin theta

Direction of force will always be perpendicular to the plane formed by V and B and determined by Right-hand rule

Point your thumb of right hand in the direction of V (In +z direction)

Point your fingers in the direction of B (in -x direction)

Now Perpendicular to the palm will point towards the direction of force, which is in -y direction

Direction of Force = Negative y-direction = -y direction

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