18.5 A wire strung across a rotating table carries a current of 0.250 A, and a uniform magnetic field of 0.500 T is applied in the
plane of the table. Consider a straight section of the wire 75.0 cm long. As the table is rotated, the magnetic force exerted on
this section will vary. What angle does the wire segment make with the field at the instant when the force is 0.0540 N? Report
the angle that is less than 90 degrees.
°Section 20 - The magnetic field around a wire
20.1 The four diagrams in the illustration show a
current-carrying electric wire from various
viewing angles. In which diagram or diagrams
is the orientation of the resulting magnetic field
correctly drawn? Check all that apply.
(a)
(b)
(c)
(d)Section 22 - Strength of the magnetic field around a wire
22.1 A long power line has a steady current of 125 A flowing through it. What is the strength of the resulting magnetic field at a
distance of 1.25 m from the wire?
T
22.2 A typical power transmission line carries a current of 1000 A about 30.0 meters above the ground. The magnetic field
generated at ground level by the current is a matter of concern to those who live nearby. (a) What is the strength of the field
at ground level below one such wire? (b) The strength of the Earth's magnetic field is about 5×10í^5 T at sea level in middle
latitudes. How close would you have to be to the power line to experience from it a magnetic field of equal strength?(a) T
(b) m
22.3 When a lightning bolt strikes a lightning rod, its current is typically conducted to the ground by a ground rod. When the
current in the rod exceeds 20.0 kA, it can no longer be confined by the rod and will arc laterally through the air to the ground.
What is the strength of the magnetic field 3.50 m from a ground rod that is conducting current at the limit of its capabilities?
Treat the ground rod as a long, straight wire.
T
22.4 A continuous stream of electrons flows along a long straight path through a piece of laboratory equipment: 4.25e+18 of them
pass through the equipment each second. What is the strength of the magnetic field created by this stream at a distance of
0.250 m?
T
22.5 You are holding a compass 3.50 m from a long straight electrical supply wire that is carrying a direct current perpendicularly
to the local direction of the Earth's magnetic field. Instead of orienting to any consistent "north" direction, the compass needle
swings aimlessly no matter how you tilt or shake the instrument. The strength of the Earth's magnetic field at your location is
5.12×10í^5 T. What is the magnitude of the current carried by the wire?
A22.6 A long, straight current-carrying wire generates a magnetic field of 1.00 μT at a distance of 1.00 m from the wire. (a) At what
distance is the field strength equal to 0.100 μT? (b) At what distance is the field strength equal to 1.00 mT? (c) What current
through the wire creates a 1.00 mT magnetic field at a distance of 1.00 m?
(a) m
(b) m
(c) A22.7 A straight horizontal wire carries a current of 3.55 μA. A proton is moving above the wire in a direction parallel to it but
opposite to the direction of the conventional current in the wire, at a constant velocity of 8.00×10^6 m/s. Assume that the force
of gravity acts on the proton and that the proton is moving parallel to the Earth's magnetic field, so that the only magnetic
force on it comes from the field generated by the current in the wire. (a) What is the magnitude of the upward force that the
magnetic field must exert on the proton to keep it at a constant velocity? (b) How far is the proton above the wire?
(a) N
(b) m(^536) Copyright 2007 Kinetic Books Co. Chapter 28 Problems