Electromagnetic Induction Quiz
Questions: 16 · 10 minutes
1. What is the SI unit of induced electromotive force?
Volt
Tesla
Weber
Ampere
2. A battery is connected to the primary coil of an ideal transformer. After the current reaches a steady value, what voltage is induced across the secondary coil?
A steady voltage equal to the battery voltage
A steadily increasing voltage
An alternating voltage determined by the turns ratio
Zero voltage because the magnetic flux is no longer changing
3. When the current through an inductor begins to increase, how is the inductor’s self-induced emf directed?
It has no direction until the current becomes steady
It reinforces the increase in current
It is always directed toward the circuit’s positive terminal
It opposes the increase in current
4. Two nearby coils are used for mutual induction. Which change would generally produce the strongest magnetic coupling between them?
Moving the coils farther apart in air
Winding both coils around a shared closed iron core
Adding resistance in series with both coils
Turning one coil so its axis is perpendicular to the other’s
5. According to Faraday’s law, what directly determines the magnitude of the average induced emf in a coil?
The amount of stationary charge on the coil
The total resistance of the coil alone
The magnetic field strength even when flux is constant
The rate at which magnetic flux linkage changes
6. A 0.40 m conducting rod moves at 3.0 m/s perpendicular to a 0.50 T magnetic field, with the rod also perpendicular to its motion. What motional emf develops across the rod?
0.15 V
1.5 V
0.60 V
6.0 V
7. A strong magnet falls through a vertical copper tube without touching its sides and descends more slowly than it would in air. What best explains the slowing?
The copper becomes permanently magnetized and holds the magnet
Eddy currents create magnetic effects that oppose the magnet’s motion
The magnet loses its magnetic field inside a conductor
Copper’s electric charge directly cancels gravity
8. An ideal transformer has 1,000 primary turns and 250 secondary turns. If 120 V AC is applied to the primary, what is the secondary voltage?
15 V
30 V
24 V
480 V
9. A coil rotates at constant angular speed in a uniform magnetic field. Why does it produce an alternating emf?
The coil’s resistance reverses after every half-turn
The magnetic field repeatedly switches off and on
The coil’s flux changes sinusoidally as its orientation changes
Charges leave the wire and then return during each rotation
10. For a flat loop in a uniform magnetic field, which expression gives its magnetic flux when θ is the angle between the field and the loop’s area normal?
BA cos θ
B divided by A cos θ
BA sin θ
B cos θ divided by A
11. A rectangular conducting loop moves at constant speed while remaining completely inside a uniform magnetic-field region. Its area and orientation stay fixed. What is the net induced emf around the loop?
It increases in proportion to the loop’s speed
It depends only on the loop’s resistance
It is zero because the flux through the loop remains constant
It alternates because the loop is moving
12. The north pole of a bar magnet moves toward a conducting loop. What magnetic pole does the near face of the loop develop while the magnet approaches?
A north pole, opposing the magnet’s approach
A south pole, attracting the approaching magnet
No pole, because only a moving loop can induce current
Alternating north and south poles at a steady rate
13. A coil’s number of turns is doubled, and the same magnetic-flux change now occurs in half the original time. How does the magnitude of its average induced emf change?
It remains unchanged
It becomes twice as large
It becomes four times as large
It becomes half as large
14. Why are transformer cores commonly constructed from thin, insulated laminations rather than one solid metal block?
To eliminate magnetic flux from the core
To restrict eddy-current paths and reduce heating
To convert alternating current directly into direct current
To increase electrical conduction between the windings
15. A stationary coil remains in a uniform magnetic field whose strength and direction do not change. What emf is induced in the coil?
An emf proportional to the field strength
An emf that increases with time
An alternating emf set by the coil resistance
Zero emf because the magnetic flux is not changing
16. The magnetic flux through each turn of a 50-turn coil decreases uniformly from 0.020 Wb to 0.005 Wb in 0.10 s. What is the magnitude of the average induced emf?
7.5 V
1.5 V
0.15 V
25 V