Page 346 - Schaum's Outline of Theory and Problems of Applied Physics

CHAP. 27] MAGNETISM 331

27.6. The following statements concern the magnetic field of a solenoid that has an iron core. Which one or more of them
are not always true?
(a) B = 0 when I = 0
(b) B increases when I increases
(c) B decreases when I decreases
(d) The direction of B changes when the direction of I changes

27.7. When a moving charged particle enters a uniform magnetic field in a direction parallel to the field lines, the
particle’s
(a) direction is changed
(b) velocity magnitude is changed
(c) energy is changed
(d) motion is unaffected

27.8. When a moving charged particle enters a uniform magnetic field in a direction perpendicular to the field lines, the
particle’s
(a) direction is changed (c) energy is changed
(b) velocity magnitude is changed (d) motion is unaffected

27.9. When a current-carrying wire loop is a magnetic field, it tends to turn so as to bring the plane of the loop
(a) parallel to the field
(b) perpendicular to the field
(c) ata45 angle to the field
◦
(d) any of the above, depending on the strength and direction of the current

27.10. If we travel around the earth, we would find that the earth’s magnetic field
(a) is the same in direction and magnitude everywhere
(b) varies in direction but not in magnitude
(c) varies in magnitude but not in direction
(d) varies in both magnitude and direction

27.11. A long, straight wire carries a current of 1.2 A. The magnetic field 8.0 mm from the wire is
(a)3.0 × 10 −8 T (c)3.6 × 10 −5 T
(b)3.0 × 10 −5 T (d)1.9 × 10 −4 T

27.12. A 200-turn solenoid is 40 mm long. If the magnetic field inside it is to be 0.010 T, the current it carries
should be
3
(a) 1.6 A (c)1.6 × 10 A
7
(b) 251 A (d)4.0 × 10 A
27.13. A magnetic force of 0.08 N acts on each centimeter of a wire that carries a 20-A current in an electric motor. If the
wire is perpendicular to the magnetic field in the motor, the magnitude of the field is
(a) 0.004 T (c) 0.4 T
(b) 0.016 T (d)40 T

27.14. Two parallel wires 800 cm long are 5 cm apart and carry currents of 20 A each in the same direction. Each wire
exerts a force on the other of

(a)1.6 × 10 −3 N, attractive (c)1.6 × 10 −3 N, repulsive
(b)1.3 × 10 −2 N, attractive (d)1.3 × 10 −2 N, repulsive