Chapter Assumptions
Elementary charge, e = 1.60×10–19 C
Mass of electron, me = 9.11×10–31 kg
Mass of proton, mp = 1.67×10–27 kg
Unless stated otherwise, use 5.00×10–5 T for the strength of the Earth's magnetic field at its surface.
Chapter 28 Problems
Conceptual Problems
C.1 While you are on a visit to Santa Claus at his workshop in the Far North, he gives you a special compass whose needle can
rotate freely in three dimensions. You try it out by standing directly above the nearby magnetic pole of the Earth. Which
direction does the north end of the compass needle point? Explain.
i. North
ii. South
iii. East
iv. West
v. Up
vi. Down
C.2 Two parallel wires conduct equal currents in opposite directions (as is the case with ordinary household electric cords). At a
point in the plane of the wires midway between them, (a) what is the direction of the combined magnetic field generated by
the two currents? (b) Do the individual fields of the wires cancel or reinforce each other there? (c) At a point in the plane of the
wires but far away to one side, do the individual fields of the wires tend to cancel or reinforce each other? Explain your
answer to part c.
(a) The field is i. parallel
ii. perpendicular
iii. at some other angleto the plane of the wires.(b) Cancel Reinforce
(c) Cancel Reinforce
C.3 A charged particle moves in a straight line through a region of space. (a) Can there be a nonzero magnetic field in this region
of space? (b) If not, explain why not, and if so, explain in what direction(s) it must point.
(a) Yes No
(b)
C.4 Two parallel wires conduct equal currents in the same direction. (a) At a point in the plane of the wires midway between
them, do the individual fields of the wires cancel or reinforce each other? (b) At a point far away from the wires, do their
individual fields tend to cancel or reinforce each other?(a) Cancel Reinforce
(b) Cancel Reinforce
C.5 Suppose you are "chirally challenged" (like one of the authors of this textbook, and, as it happens, the physicist Heinrich
Hertz): All too often, you cannot accurately recall which is right and which is left. Not only do your driving friends refuse to let
you "navigate," but you occasionally use your left hand by mistake when attempting to find the direction of the force exerted
on a moving proton by a magnetic field. (a) Do you get the right direction anyway? (b) For which of the following particles
does your left thumb point in the direction of the force?
(a) Yes No
(b) i. Positron
ii. Neutron
iii. Electron
iv. Neutrino
v. Proton
C.6 Do perpendicular straight wires that carry a steady current, and are almost touching, exert a net force on each other? Explain
whether the wires influence each other in any way at all.
Yes No