Page 347 - Schaum's Outline of Theory and Problems of Applied Physics

332 MAGNETISM [CHAP. 27

Supplementary Problems

27.1. An observer is able to measure electric, magnetic, and gravitational fields. Which of these does she detect when
(a) a proton moves past her, and (b) she moves past a proton?

27.2. A beam of electrons that are moving slowly at first are accelerated to higher and higher velocities. What happens to
the diameter of the beam as this happens?
27.3. An electric current is flowing south along a power line. What is the direction of the magnetic field above it?
Below it?
27.4. A charged particle moves through a magnetic field perpendicular to B. Is the particle’s energy affected? Is its
momentum?
27.5. In a sketch of magnetic lines of force, what is the significance of lines of force that are closer in a particular region
than they are elsewhere?

27.6. A negative charge is moving west when it enters a magnetic field directed vertically downward. In what direction is
the force on the charge?

27.7. A wire carrying a current is placed in a magnetic field B. (a) Under what circumstances, if any, will the force on the
wire be zero? (b) Under what circumstances will the force on the wire be a maximum?

27.8. Under what circumstances, if any, does a current-carrying wire loop not tend to rotate in a magnetic field?

27.9. The magnetic field 5 cm from a certain straight wire is 10 −4 T. Find the current in the wire.
27.10. How far away from a compass should a wire carrying a 1-A current be located if its magnetic field at the compass
is not to exceed 1 percent of the earth’s magnetic field, which is typically 3 × 10 −5 T?
27.11. Two parallel wires 20 cm apart carry currents of5Ainthe same direction. Find the magnetic field between the wires
5 cm from one of them and 15 cm from the other.
27.12. What should the current be in a wire loop 1 cm in radius if the magnetic field in the center of the loop is to be 0.01 T?

27.13. What is the magnetic field inside a solenoid wound with 20 turns per centimeter when the current in it is 5 A?

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27.14. An electron in a television picture tube travels at 3 × 10 m/s. Does the earth’s gravitational field or its magnetic
field exert the greater force on the electron? Assume v is perpendicular to B.
27.15. (a) A wire 1 m long is perpendicular to a magnetic field of 0.01 T. What is the force on the wire when it carries a
current of 10 A? (b) What is the force on the wire when it is parallel to the magnetic field?
27.16. A horizontal wire 10 cm long whose mass is 1 g is to be supported magnetically against the force of gravity. The
current in the wire is 10 A and goes from north to south. (a) What should be the direction of the magnetic field?
(b) What should its magnitude be?

27.17. The starting motor of a certain car is connected to the battery by a pair of cables that are 8 mm apart for a distance
of 50 cm. Find the force between the cables when the current is 100 A.

27.18. An alternating current that varies with time according to the formula I = I max sin ωt is sent through a solenoid with
an iron core. (a) Does the magnetic intensity in the core also vary sinusoidally with time? (b) Does the magnetic
field?

27.19. The magnetic intensity H inside an air-core solenoid 25 cm long that is wound with 300 turns of wire is 600 A/m.
(a) What is the current in the solenoid? (b) What is the magnetic field B inside the solenoid?