P7 - Magnetism and Electromagnetism 2 - 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 wire which when current passes through creates a strong magnetic field

Question 4

Describe the magnetic field found inside a solenoid

Answer 4

Strong and uniform

Question 5

What is an electromagnet ?

Answer 5

• a solenoid with an added iron core
• adding the iron core increases the strength of the magnetic field

Question 6

What is the motor effect ?

Answer 6

When a force is exerted between a magnetic field and a current-carrying conductor placed in that field

Question 7

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

Answer 7

Fleming’s Left-Hand Rule

Question 8

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

Answer 8

The forefinger points in the direction of the magnetic field

Question 9

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

Answer 9

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

Question 10

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

Answer 10

• The magnitude of the current flowing through the conductor
• the strength of the magnetic field that the conductor is placed in

Question 11

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

Answer 11

The direction of the force is reversed

Question 12

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 12

The strength of the force is increased

Question 13

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

Answer 13

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

Question 14

What is the unit for magnetic flux density ?

Answer 14

Tesla , T

Question 15

How does an electric motor work ?

Answer 15

• 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 16

How do loudspeakers make use of the motor effect ?

Answer 16

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

Question 17

Explain how a loudspeaker works

Answer 17

• 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 18

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

Answer 18

• the frequencyof the a.c current is altered
  -this creates a different frequency of vibration in the cone