12.2 Electromagnetism & The Motor Effect

Higher Only

A current-carrying wire is placed between two magnetic poles as shown in the diagram below. It experiences an upwards force.

What is the orientation of the magnetic poles?

 

	Left magnet	Right magnet
A	N	N
B	S	N
C	N	S
D	S	S

Higher Only

Figure 1 shows a wire connected to a circuit inside a uniform magnetic field.

Figure 1

The magnetic flux density of the field is 0.82 N/A m. 

The length of the wire is 40 mm with 30 mm inside the field. 

The size of the force due to the magnetic field on the wire is 0.073 N.

Calculate

Higher Only

The circuit in Figure 1 is turned so the wire is now placed horizontally.

Explain the effect this has on the motion of the wire.

A current-carrying wire is placed into a magnetic field as shown in the diagram. The wire experiences a force.

In which direction is the force?

   A   PO

   B   ST

   C   QR

   D   OP

Two long, thin magnets are held with their S-poles facing each other.

The force, F, between the magnets can be calculated using the equation

where 

   k is a constant value

    d is the distance between the magnets.

When the magnets are 3.0 cm apart, the force between the magnets is 1.5 N.

Calculate the separation of the magnets when the force between them is 2.6 N.

Explain what happens if the magnets are held the same initial distance apart but with the S-pole of one magnet now facing the N-pole of the other magnet.

Figure 6 shows some objects and words describing these objects.

Draw one line from each object to its description.

Figure 6

Figure 7 shows a wire passing through a piece of card.

The wire carries an electric current.

Figure 7

[1]

[1]

A student measures the strength of the magnetic field at several distances from the wire in Figure 7.

Figure 8 shows most of the student’s results.

Figure 8

Figure 9 shows two extra sets of results.

mT is a unit of strength of a magnetic field.

Figure 9

[2]

[1]

[2]

change in strength of magnetic field = ................................ mT

[1]

 
                                                    
The teacher has a bar magnet, a coil of wire and a sensitive voltmeter.

[1]

[4]

Higher Only

There is a changing magnetic field in the core of a transformer.

[2]

[3]

............................................... turns

Higher Only

Figure 1 shows equipment which demonstrates the motor effect.

Figure 1

A piece of copper wire (Q) is placed on two bare wires connected to a cell and switch.

Describe what happens to wire Q when the switch is closed.

Higher Only

Describe any differences in the motion of Q for the following changes:

Higher Only

Figure 2

A direct current passes through the coil, then the metal bars move apart.

Explain why the metal bars move apart.

Higher Only

The d.c. supply is removed and the metal rods return to their starting places.

Suggest a material that the metal rods could be made from. Explain why you chose this.

Higher Only

Figure 1

State the name of the phenomenon causing this rotation.

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Using Fleming's left hand rule, state the direction that the left side of the coil moves in Figure 1.

Higher Only

A current of 2.5 A flows in the coil, which is 0.10 m long and 0.10 m wide.

If the magnetic flux density is 0.10 T, calculate the force on the left side of the coil.  

Higher Only

Explain why a force acts on the coil when a current passes through it.