20) A charged particle moves across a constant magnetic field. The magnetic force on this particle
A) changes the particle's speed.
B) causes the particle to accelerate.
C) is in the direction of the particle's motion.
D) changes the particle's speed causing the particle to accelerate.
Answer: B
21) A charged particle is injected into a uniform magnetic field such that its velocity vector is perpendicular to the
magnetic field vector. Ignoring the particle's weight, the particle will
A) move in a straight line.
B) follow a spiral path.
C) move along a parabolic path.
D) follow a circular path.
Answer: D
22) A charged particle is observed traveling in a circular path in a uniform magnetic field. If the particle had been
traveling twice as fast, the radius of the circular path would be
A) twice the original radius.
B) four times the original radius.
C) one-half the original radius.
D) one-fourth the original radius.
Answer: A
23) A particle carrying a charge of +e travels in a circular path in a uniform magnetic field. If instead the particle
carried a charge of +2e, the radius of the circular path would have been
A) twice the original radius.
B) four times the original radius.
C) one-half the original radius.
D) one-fourth the original radius.
Answer: C
24) At a particular instant, a proton moves eastward at speed V in a uniform magnetic field that is directed straight
downward. The magnetic force that acts on it is
A) zero.
B) directed upward.
C) directed to the north.
D) directed to the south.
Answer: C
25) An electron has an initial velocity to the south but is observed to curve upward as the result of a magnetic field.
The direction of the magnetic field is
A) to the west.
B) to the east.
C) upward.
D) downward.
Answer: A
27) The magnetic field produced by a long straight current-carrying wire is
A) proportional to both the current in the wire and the distance from the wire
B) proportional to the current in the wire and inversely proportional to the distance from the wire.
C) inversely proportional to the current in the wire and proportional to the distance from the wire.
D) inversely proportional to both the current in the wire and the distance from the wire.
Answer: B
29) Two long parallel wires placed side-by-side on a horizontal table carry identical size currents in opposite
directions. The wire on your right carries current toward you, and the wire on your left carries current away from
you. From your point of view, the magnetic field at the point exactly midway between the two wires
A) points up.
B) points down.
C) points toward you.
D) is zero.
Answer: B
30) Two long parallel wires placed side-by-side on a horizontal table carry identical current straight toward you.
From your point of view, the magnetic field at the point exactly between the two wires
A) points up.
B) points down.
C) points toward you.
D) is zero.
Answer: D
32) A long straight wire carries current toward the east. A proton moves toward the east alongside and just south of
the wire. What is the direction of the force on the proton?
A) north
B) south
C) up
D) down
Answer: A