Topic 4.6 - Electromagnetic Effects

Question 1

What is electromagnetic induction?

Answer 1

The production of a potential difference caused by relative movement between a conductor and a magnetic field.

Question 2

In what direction is the potential difference induced?

Answer 2

In the opposite direction to the movement which produced it.

Question 3

When is a current produced?

Answer 3

When the ends of the coil are connected to a complete circuit.

Question 4

How can you increase the induced EMF?

Answer 4

• Moving the wire more quickly
• Increasing the length of wire
• Using a stronger magnetic field

Question 5

How can you work out the direction of the induced current?

Answer 5

Using Fleming’s right hand rule.

Question 6

How are electric generators set up?

Answer 6

In the same way as a motor, with a rectangular loop of wire between permanent magnets. The main difference is the presence of a turbine to spin the coil.

Question 7

Describe how an electrical generator works

Answer 7

• A turbine spins the coil of wire between magnets
• The wire cuts through the magnetic field experiencing a changing magnetic field
• A potential difference is induced
• A current is produced

Question 8

What kind of current is produced by an ordinary generator?

Answer 8

An alternating current.

Question 9

How does a split ring commutator work?

Answer 9

It disconnects and reconnects the wires every half rotation, switching the current so the motor spins continuously.

Question 10

How do transformers work?

Answer 10

• An alternating current flows through the primary coil, producing an alternating magnetic field.
• This causes the secondary coil to experience a changing magnetic field, inducing a potential difference, which produces an alternating current in the secondary coil.

Question 11

Why do step up transformers increase voltage?

Answer 11

There are more coils experiencing the change, so a larger p.d. is induced.

Question 12

State one assumption used in transformer calculations

Answer 12

The transformer is 100% efficient (the power is assumed to be the same in both coils).

Question 13

What is produced around a current carrying wire?

Answer 13

A magnetic field.

Question 14

How can you determine the direction of a magnetic field around a wire?

Answer 14

• Using the Right Hand Grip Rule.
• Produce a thumbs-up shape with your right hand and point your thumb in the direction of the flow of current.
• The field lines wrap around in the direction of your fingers.

Question 15

What is a solenoid?

Answer 15

A coil of wire with a magnetic field, which can be used as an electromagnet.

Question 16

How does coiling a wire affect the magnetic field?

Answer 16

It increases the field strength, as the magnetic fields of each turn of wire are added together.

Question 17

How can you increase the strength of a solenoid magnet?

Answer 17

• Using an iron core to carry field lines (as they travel more easily through metal than air)
• Increase the number of turns in the coil
• Increase the current

Question 18

What is the motor effect?

Answer 18

If a current-carrying wire is placed in a magnetic field it experiences a force, pushing the wire out of/away from the field.

Question 19

Describe the mechanism of the motor effect

Answer 19

• When a current-carrying wire produces a magnetic field within the field of a permanent magnet, the two fields interact.
• The wire experiences a force pushing it away from the magnetic field, at right angles to the direction of the permanent field and the current.

Question 20

How can you predict the direction of the motor effect?

Answer 20

Using Fleming’s left hand rule:

• Thumb = Movement
• First finger = Field
• Second finger = Current

Question 21

What is conventional current?

Answer 21

A model for current which flows in the opposite direction to electrons. Conventional current flows from positive to negative.

Question 22

What kind of current is used in Fleming’s rule?

Answer 22

Conventional current.

Question 23

Which factors affect the strength of the motor force?

Answer 23

• The length of wire placed in the field
• The current in the wire
• The strength of the permanent field