P4.2 Uses of Magnetism

Question 1

What is an Electromagnet?

Answer 1

• A solenoid with an added Iron Core

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

Question 2

What is the motor effect?

Answer 2

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

Question 3

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

Answer 3

Fleming’s Left hand Rule

Question 4

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

Answer 4

Index - magnetic field
Middle - Current flow
Thumb - Force

Question 5

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

Answer 5

• The magnitude of the current flowing through the conductor

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

Question 6

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

Answer 6

The direction of the force is reversed

Question 7

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 7

The strength of the force is increased

Question 8

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

Answer 8

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

Question 9

What is the unit for magnetic flux density?

Answer 9

Tesla

Question 10

How does an electric motor work?

Answer 10

• A coil of wire, carrying 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 11

How do loudspeakers make use of the motor effect?

Answer 11

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

Question 12

Explain how a loud speaker works?

Answer 12

• 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 created a second magnetic field, which interacts with the permanent field.
• This produces a force which causes the cone to vibrate

Question 13

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

Answer 13

• The frequency of a.c current is changed

- This creates a different vibration in the cone

Question 14

What happens when an electrical conductor moves relative to a magnetic field?

Answer 14

A potential difference is induced across the ends of the conductor.

Question 15

What happens to an electrical conductor when there is a change to the magnetic field that it is placed in?

Answer 15

A potential difference is induced across the ends of the conductor

Question 16

What is a requirement for an induced potential difference to cause a current flow?

Answer 16

The conductor must form a closed loop or be part of a complete circuit

Question 17

What can be said about the direction of the magnetic field produced by an induced current?

Answer 17

• The direction of the field is such that it opposes the change that induced the current
• This change is either the movement of the conductor or a change to the field

Question 18

If there is a change in the magnetic field around the a conductor, explain what changes occur in the conductor.

Answer 18

• A p.d is induced across ends
• This drives a current
• The direction of the induced current is such that it creates a magnetic field that opposes the change in the existing field.