Sec 4 Revision Package - Magnetism and Electromagnetism

The diagram shows how a steel bar can be magnetised.

Which statement describes how the steel bar can be demagnetised?

• Reverse the d.c. supply and gradually decrease the current in the circuit.

• Reverse the d.c. supply and gradually increase the current in the circuit.

• Use an a.c. supply and gradually decrease the current in the circuit.

• Use an a.c. supply and gradually increase the current in the circuit.

A copper wire carrying a current is held between the poles of a magnet.

The current in the wire can be reversed.

The poles of the magnet can be changed over.

In how many of the four directions shown can a force act on the wire?

• 1

• 2

• 3

• 4

The diagram shows the pattern and direction of the magnetic field around two bar magnets.

Which diagram shows the poles of the two magnets?

• 
• 
• 
• 

Three metal bars, X, Y, and Z, exhibit the following magnetic properties:

X is attracted by both ends of Y.

Y can be repelled by Z.

Which row correctly describes X, Y, and Z?

• A) X: magnetised,

  Y: magnetised,

  Z: unmagnetised

• B) X: magnetised,

  Y: unmagnetised,

  Z: magnetised

• C) X: unmagnetised,

  Y: magnetised,

  Z: magnetised

• D) X: unmagnetised,

  Y: magnetised,

  Z: unmagnetised

A current-carrying wire is in a magnetic field.

The direction of electron flow is shown.

What is the direction of the force on the wire?

• in the opposite direction to the magnetic field

• in the same direction as the magnetic field

• into the paper

• out of the paper

The diagram shows two separate bar magnets.

What are the poles at X and Y?

• X: N,

  Y: N

• X: N,

  Y: S

• X: S,

  Y: N

• X: S,

  Y: S

A vertical wire carries a current.

The diagram shows the magnetic field around the wire, when viewed from above.

The poles of a magnet are placed either side of the wire.

What is the direction of the force on the wire caused by the magnet?

• 
• 
• 
• 

The diagram shows an electromagnet and a permanent magnet.

The electromagnet attracts the permanent magnet.

The permanent magnet is removed and three compasses are placed around the electromagnet.

Which diagram shows the correct directions for the compass needles?

• 
• 
• 
• 

A current-carrying coil in a magnetic field experiences a turning effect which causes it to rotate.

The diagrams show the possible arrangements of field and current flow around the coil.

In which diagrams does the coil rotate in an anti-clockwise direction?

• A) P and Q

• B) P and R

• C) Q and R

• D) Q and S

A piece of magnetised steel is placed inside a coil connected to a power supply.

Which method demagnetises the steel?

• Supply alternating current and gradually decrease the voltage to zero

• Supply alternating current and gradually increase the voltage from zero

• Supply direct current and gradually decrease the voltage to zero

• Supply direct current and gradually increase the voltage from zero