Lesson test: Induction

1.[2p]
Why did the experimenters of the 1820s who put coils near strong magnets find no current?

A steady magnetic field induces nothing; only a changing flux does

Correct

Their galvanometers were not sensitive enough

The answer is: A steady magnetic field induces nothing; only a changing flux does

They used the wrong metal for the coils

The answer is: A steady magnetic field induces nothing; only a changing flux does

The magnets were too far from the coils

The answer is: A steady magnetic field induces nothing; only a changing flux does

2.[3p]
A coil of 300 turns encloses 20 cm² perpendicular to a field that falls steadily from 0.50 T to zero in 0.10 s. What EMF appears, in volts?

CorrectNot quite: 3.0

3.[3p]
Which of these change the flux through a circuit and so induce an EMF?

Select all that apply

The field strength through it rises

Correct

The circuit is stretched, changing its area

Correct

The circuit is rotated relative to the field

Correct

The circuit sits still in a strong steady field

The answer is: The field strength through it rises, The circuit is stretched, changing its area, The circuit is rotated relative to the field

4.[3p]
A rod 0.30 m long slides at 5.0 m/s along rails in a 0.60 T field, with a 3.0 Ω resistance closing the circuit. What current flows, in amperes?

CorrectNot quite: 0.30

5.[3p]
Lenz's law follows from which principle?

Conservation of energy, since the opposite sign would let energy appear from nothing

Correct

Conservation of charge at a junction

The answer is: Conservation of energy, since the opposite sign would let energy appear from nothing

The fact that magnetic field lines close on themselves

The answer is: Conservation of energy, since the opposite sign would let energy appear from nothing

Newton's third law applied to the magnet and the coil

The answer is: Conservation of energy, since the opposite sign would let energy appear from nothing

6.[3p]
A generator coil of 400 turns and area 50 cm² rotates at 25 revolutions per second in a 0.30 T field. What is the peak EMF, in volts?

CorrectNot quite: 94.2

7.[2p]
A magnet dropped down a copper pipe falls slowly because copper is attracted to magnets.

True

The answer is: False

False

Correct

8.[3p]
Moving the magnet and moving the loop give the same EMF, but classical theory explains them differently. What did Einstein take from that?

That the asymmetry is in the explanation, not the phenomena, and that absolute rest is an empty notion

Correct

That Faraday's law must be only approximately true

The answer is: That the asymmetry is in the explanation, not the phenomena, and that absolute rest is an empty notion

That the magnetic force does work after all

The answer is: That the asymmetry is in the explanation, not the phenomena, and that absolute rest is an empty notion

That the two cases give slightly different EMFs when measured precisely

The answer is: That the asymmetry is in the explanation, not the phenomena, and that absolute rest is an empty notion

9.[3p]
Why does electric potential stop being defined in a region with a changing magnetic field?

The circulation of the electric field round a closed path is no longer zero, so the work done is not a function of position

Correct

Because the electric field becomes too strong to measure

The answer is: The circulation of the electric field round a closed path is no longer zero, so the work done is not a function of position

Because charge is no longer conserved there

The answer is: The circulation of the electric field round a closed path is no longer zero, so the work done is not a function of position

Because the magnetic field has no potential either

The answer is: The circulation of the electric field round a closed path is no longer zero, so the work done is not a function of position

1.[2p] Why did the experimenters of the 1820s who put coils near strong magnets find no current?

2.[3p] A coil of 300 turns encloses 20 cm² perpendicular to a field that falls steadily from 0.50 T to zero in 0.10 s. What EMF appears, in volts?

3.[3p] Which of these change the flux through a circuit and so induce an EMF?

4.[3p] A rod 0.30 m long slides at 5.0 m/s along rails in a 0.60 T field, with a 3.0 Ω resistance closing the circuit. What current flows, in amperes?

5.[3p] Lenz's law follows from which principle?

6.[3p] A generator coil of 400 turns and area 50 cm² rotates at 25 revolutions per second in a 0.30 T field. What is the peak EMF, in volts?

7.[2p] A magnet dropped down a copper pipe falls slowly because copper is attracted to magnets.

8.[3p] Moving the magnet and moving the loop give the same EMF, but classical theory explains them differently. What did Einstein take from that?

9.[3p] Why does electric potential stop being defined in a region with a changing magnetic field?

1.[2p]
Why did the experimenters of the 1820s who put coils near strong magnets find no current?

2.[3p]
A coil of 300 turns encloses 20 cm² perpendicular to a field that falls steadily from 0.50 T to zero in 0.10 s. What EMF appears, in volts?

3.[3p]
Which of these change the flux through a circuit and so induce an EMF?

4.[3p]
A rod 0.30 m long slides at 5.0 m/s along rails in a 0.60 T field, with a 3.0 Ω resistance closing the circuit. What current flows, in amperes?

5.[3p]
Lenz's law follows from which principle?

6.[3p]
A generator coil of 400 turns and area 50 cm² rotates at 25 revolutions per second in a 0.30 T field. What is the peak EMF, in volts?

7.[2p]
A magnet dropped down a copper pipe falls slowly because copper is attracted to magnets.

8.[3p]
Moving the magnet and moving the loop give the same EMF, but classical theory explains them differently. What did Einstein take from that?

9.[3p]
Why does electric potential stop being defined in a region with a changing magnetic field?