The motor effect

Question 1

What is produced when current flows through a conducting wire?

Answer 1

A magnetic field is produced around the wire

Question 2

What determines the strength of the magnetic field around a current-carrying wire?

Answer 2

• The magnitude of the current flowing through the wire

- The distance from the wire

Question 3

What is a solenoid?

Answer 3

A coil of current-carrying wire that produces a magnetic field

Question 4

Describe the magnetic field found inside a solenoid

Answer 4

Strong and uniform

Question 5

What is electromagnetism?

Answer 5

The interaction between electricity and magnetism

Question 6

What is an electromagnet?

Answer 6

• A solenoid with an added iron core

- Adding the iron core increases the strength of the magnetic field

Question 7

What is the motor effect?

Answer 7

When a current-carrying wire is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in. This causes the magnet & the conductor to exert a force on each other - this can cause the wire to move

Question 8

What rule is used to determine the force experienced due to the motor effect?

Answer 8

Fleming’s Left-Hand Rule

Question 9

When using Fleming’s left hand rule what does the forefinger represent?

Answer 9

The forefinger points in the direction of the magnetic field

Question 10

When using Fleming’s left hand rule what does the second finger represent?

Answer 10

The second finger points in the direction of current flow in the conductor

Question 11

What factors affect the size of the force on a current-carrying wire in a magnetic field?

Answer 11

• The magnitude of the current flowing through the conductor

- The strength of the magnetic field that the conductor is placed in

Question 12

If the direction of current in a current-carrying wire placed in a uniform magnetic field is reversed, what happens to the force?

Answer 12

The direction of the force is reversed

Question 13

If the strength of the current in a current-carrying wire placed in a uniform magnetic field is increased, what happens to the force?

Answer 13

The strength of the force is increased

Question 14

What criteria must be met for the equation linking force, magnetic flux density, current and length hold?

Answer 14

The conductor must be at right-angles to the magnetic field it is placed in

Question 15

What is the unit used for magnetic flux density?

Answer 15

Tesla (T)

Question 16

How does an electric motor work?

Answer 16

• A coil of wire, carrying a current, is placed in a magnetic field
• The forces on the two sides perpendicular to the field experience forces in opposite directions
• This causes a rotational effect

Question 17

How do loudspeakers make use of the motor effect?

Answer 17

The motor effect is used to convert variations in the current of an electrical circuit into the pressure variations which produce audible sound.

Question 18

Explain how a loudspeaker works

Answer 18

• A cone with a wire wrapped around it is connected to an a.c power supply and is placed in a permanent magnetic field
• When current flows through the wire, it creates a second magnetic field, which interacts with the permanent field
• This produces a force which causes the cone to vibrate

Question 19

How is the pitch of the sound from a loudspeaker changed?

Answer 19

• The frequency of the a.c current is altered

- This creates a different frequency of vibration in the cone