Lesson test: Sources of magnetism

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Sources of magnetism

1.[3p]
How does the Biot-Savart law differ in character from Coulomb's law?

Its field points at right angles to the line from source to point, rather than along it

Correct

It falls off as the inverse cube rather than the inverse square

The answer is: Its field points at right angles to the line from source to point, rather than along it

It has no constant in front of it

The answer is: Its field points at right angles to the line from source to point, rather than along it

Its source is a scalar rather than part of a vector

The answer is: Its field points at right angles to the line from source to point, rather than along it

2.[2p]
A long straight wire carries 20 A. What is the magnetic field 5.0 cm from it, in microtesla?

CorrectNot quite: 80

3.[2p]
Two long parallel wires carrying current in the same direction repel each other.

True

The answer is: False

False

Correct

4.[3p]
Two long parallel wires 10 cm apart each carry 25 A. What is the force per metre between them, in millinewtons per metre?

CorrectNot quite: 1.25

5.[3p]
A solenoid 20 cm long is wound with 500 turns and carries 3.0 A. What is the field inside it, in millitesla?

CorrectNot quite: 9.42

6.[3p]
Why is there no magnetic potential analogous to the electric one?

The circulation of the magnetic field round a closed path is not zero

Correct

Because the magnetic force does no work

The answer is: The circulation of the magnetic field round a closed path is not zero

Because magnetic field lines close on themselves

The answer is: The circulation of the magnetic field round a closed path is not zero

Because $μ_{0}$ is not exactly $4 π \times 10^{- 7}$

The answer is: The circulation of the magnetic field round a closed path is not zero

7.[2p]
What does the statement that the magnetic flux out of any closed surface is zero assert?

That there is no magnetic charge, so field lines close on themselves rather than ending

Correct

That magnetic fields cannot pass through a closed surface

The answer is: That there is no magnetic charge, so field lines close on themselves rather than ending

That the total magnetic field of the universe is zero

The answer is: That there is no magnetic charge, so field lines close on themselves rather than ending

That every magnetic field is produced by a current

The answer is: That there is no magnetic charge, so field lines close on themselves rather than ending

8.[2p]
Reaching a field of 2.5 T with a solenoid requires how many ampere turns per metre, in units of $10^{6}$ ?

CorrectNot quite: 1.99

9.[3p]
Match each magnetic behaviour to its description.

Paramagnetism
Diamagnetism
Ferromagnetism
Above the Curie temperature

alignment destroyed by heat
a weak response opposing the applied field
spontaneous alignment within domains
weak alignment that vanishes with the field

Show the answer

Paramagnetism: weak alignment that vanishes with the field Diamagnetism: a weak response opposing the applied field Ferromagnetism: spontaneous alignment within domains Above the Curie temperature: alignment destroyed by heat

1.[3p] How does the Biot-Savart law differ in character from Coulomb's law?

2.[2p] A long straight wire carries 20 A. What is the magnetic field 5.0 cm from it, in microtesla?

3.[2p] Two long parallel wires carrying current in the same direction repel each other.

4.[3p] Two long parallel wires 10 cm apart each carry 25 A. What is the force per metre between them, in millinewtons per metre?

5.[3p] A solenoid 20 cm long is wound with 500 turns and carries 3.0 A. What is the field inside it, in millitesla?

6.[3p] Why is there no magnetic potential analogous to the electric one?

7.[2p] What does the statement that the magnetic flux out of any closed surface is zero assert?

8.[2p] Reaching a field of 2.5 T with a solenoid requires how many ampere turns per metre, in units of 106?

9.[3p] Match each magnetic behaviour to its description.

1.[3p]
How does the Biot-Savart law differ in character from Coulomb's law?

2.[2p]
A long straight wire carries 20 A. What is the magnetic field 5.0 cm from it, in microtesla?

3.[2p]
Two long parallel wires carrying current in the same direction repel each other.

4.[3p]
Two long parallel wires 10 cm apart each carry 25 A. What is the force per metre between them, in millinewtons per metre?

5.[3p]
A solenoid 20 cm long is wound with 500 turns and carries 3.0 A. What is the field inside it, in millitesla?

6.[3p]
Why is there no magnetic potential analogous to the electric one?

7.[2p]
What does the statement that the magnetic flux out of any closed surface is zero assert?

8.[2p]
Reaching a field of 2.5 T with a solenoid requires how many ampere turns per metre, in units of $10^{6}$ ?

9.[3p]
Match each magnetic behaviour to its description.