Download 272 prac3

1. Which of the following statements concerning the magnetic force on a charged
particle in a magnetic field is true?
(a) It is a maximum if the particle is stationary.
(b) It is zero of the particle moves perpendicular to the field.
(c) It is maximum of the particle moves parallel to the field
(d) It acts in the direction of motion for a positively charged particle.
(e) It depends on the component of the particle’s velocity that is perpendicular to the
field.
2. A compass needle, which is a magnetic dipole, is in a magnetic field with its northseeking pole pointing in the positive direction of B. The net force on the compass
needle is
(a) in the negative direction of B
(b) in the positive direction of B
(c) at right angles to B
(d) at right angles to the plane of B and the needle
(e) none of the above
3. A proton traveling due east in a region that contains only a magnetic field xperiences
a vertically upward force away from the surface of the earth. The magnetic field must
be directed
(a) north
(b) east
(c) south
(d) west
(e) down
4. A charged particle is moving in a uniform, constant magnetic field. Which of the
following statements concerning the magnetic force exerted on the particle is false?
(a) it does no work on the particle
(b) it increases the speed of the particle
(c) it changes the velocity of the particle (d) it can act only on a particle in motion
(e) it does not change the kinetic energy of the particle
5. A proton traveling due north enters a region that contains both a magnetic field and
an electric field. The electric field lines point due west. It is observed that the proton
continues to travel in a straight line due north. In which direction must the magnetic
field lines point?
(a) up
(b) down
(c) east
(d) west
(e) south
6. What is the direction of the magnetic field around a wire carrying a current
perpendicularly into this page?
(a) parallel to and in the same direction as the current flow
(b) parallel to but oppositely directed to the current flow
(c) counterclockwise around the wire in the plane of the page
(d) clockwise around the wire in the plane of the page
(e) none of the above
7. Two current-carrying wires are perpendicular to each other. The current in one flows
vertically upward and the current in the other flows horizontally east. The horizontal
wire is 1 meter south of the vertical wire. What is the direction on the net magnetic
force on the horizontal wire?
(a) north
(b) east
(c) west
(d) south
(e) there is no force on the horizontal wire
8. A conducting loop lies in the plane of this page and carries a clockwise induced
current. which of the following statements could be true?
(a) a constant magnetic field is directed into the page
(b) a constant magnetic field is directed out of the page
(c) an increasing magnetic field is directed into the page
(d) a decreasing magnetic field is directed into the page
(e) a decreasing magnetic field is directed out of the page
9. A conducting loop of wire is placed in a magnetic field that is normal to the plane of
the loop. Which of the following actions will not result in an induced current in the
loop?
(a) decrease the area of the loop
(b) increase the strength of the magnetic field
(c) decrease the strength of the magnetic field
(d) rotate the loop about an axis that is parallel to the field and passes through the
center of the loop
(e) rotate the loop about an axis that is perpendicular to the field and passes through
the center of the loop
10. A current in a solenoid is decreased to ½ of its original value. Then, the selfinductance of the solenoid
(a) decreases by a factor of 2
(b) increases by a factor of 2
(c) decreases by a factor of 4
(d) increases by a factor of 4
(e) will not change
11. A transformer has 450 turns in its primary coil and 30 turns in its secondary coil.
Which of the following statements is true?
(a) it is a step-up transformer
(b) the turns ratio is 15
(c) the ratio of the voltages Vs/Vp is 15
(d) the ratio of the current Is/Ip is 0.067
(e) the power delivered to the secondary must be the same as that delivered to the
primary
12. A long straight wire is in the same plane as a rectangular, conducting loop. The wire
carries a constant current I as shown. Which of the following statements is true if the
wire is suddenly moved toward the loop?
(a) there will be no induced emf and no induced current
(b) there will be an induced emf and no induced current
(c) there will be an induced current that is clockwise around the loop
(d) there will be an induced current that is counterclockwise around the loop
(e) there will be an induced electric field that is clockwise around the loop
13. A circular loop of wire rotates about a diameter in a magnetic field that is
perpendicular to the axis of rotation. Looking in the direction of the field at the loop
the induced current is
(a) always clockwise (b) always counterclockwise
(c) sometimes clockwise and sometimes counterclockwise
(d) clockwise on the lower half of the loop and counterclockwise in the upper half
(e) clockwise on the upper half of the loop and counterclockwise in the lower half
14. A merry-go-round has an area of 300 m2 and spins at 2 rpm about a vertical axis at a
place where the Earth’s magnetic field is vertical and has a magnitude of 5 x 10-5 T.
The emf around the rim is
(a) 0.5 mV
(b) 3.1 mV
(c) 15 mV
(d) 30 mV
(e) zero
15. An 8.0 mH inductor and a 2.0 resistor are wired in series to a 20 V ideal battery. A
switch is closed at t = 0, at which time the current is zero. After a long time, the
current in the resistor and the current in the inductor are:
(a) 0, 0
(b) 10 A, 10 A
(c) 2.5 A, 2.5 A
(d) 10 A, 2.5A
(e) 10 A, 0
16. In each of the following operations, energy is expended. The LEAST percentage of
returnable electrical energy will be yielded by:
(a) charging a capacitor
(b) charging a storage battery
(c) sending a current through a resistor
(d) establishing a current through an inductor
(e) moving a conduction rod through a magnetic field