(B)
(C)
(D)
(E)
Answers
1 . E—Using the right hand rule (RHR) for magnetic fields around current carrying wires, we determine
that the magnetic field rotates clockwise around the left wire and counterclockwise around the right
wire. Thus, choices A, B, and C cannot be correct because the two B-fields combine in the downward
direction. Thus, the viable options are choices D and E. Using the equation , we see that
the left wire, with twice the current, must also have twice the radius to produce the same size B-field
as the right wire: . Choice E satisfies this condition.2 . D —Using the right hand rule (RHR) for a current carrying wire, we can determine that the magnetic
field around the wire point is the –z direction in the vicinity of the proton. Using the RHR for forces
on moving charges, we can determine that the proton will experience a magnetic force in the +x
direction.
3 . D —For a charged particle to cross straight through crossed perpendicular magnetic and electric
fields, the electric and magnetic forces on the charge must cancel each other out: