1.9 Electromagnetism

At which parts of a magnet are the magnetic forces strongest?

The poles of the magnet

What happens when 2 magnets are brought close to each other?

They exert a force on each other

What type of force is exerted if two like poles of a magnet are brought close to each other?

A repulsive, non-contact force

What type of force is exerted if two opposite poles of a magnet are brought close to each other?

An attractive, non-contact force

What is a magnetic field?

The region surrounding a magnet where another magnet or magnetic material experiences a non-contact force.

What is produced when current flows through a conducting wire?

A magnetic field is produced around the wire

How do you work out the direction of the field around a current-carrying wire?

Using the right hand grip rule

Thumb= direction of current

Fingers= direction of magnetic field

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

- The size of the current flowing through the wire

- The coils around the wire

- The distance from the wire

What is a solenoid?

A coil of wire which when current passes through creates a strong magnetic field.

Describe the magnetic field found inside a solenoid.

Strong and uniform

What is an electromagnet?

- A solenoid with an added iron core

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

What is the motor effect?

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

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

Fleming's Left-Hand Rule

How do you use Fleming's Left-hand rule?

ThuMb- Motion

First finger- Field

seCond finger- Current

The thumb and fingers should be at right angles to each other.

How does an electric motor work?

As current will flow in opposite directions on each side of the coil, the force produced from the magnetic field acts upwards on one side of the coil and downwards on the other.. This will cause the coil to rotate on its axis.

Where is a split ring commutator placed and what does it do?

It is placed in an electric motor.

It reverses current every half turn to ensure that force on the left of the coil is always upwards and force on the right of the coil is downwards. This causes the coil to turn continuously in one direction.

What type of current is used in an electric motor?

Direct current

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

- The size of the current flowing through the conductor

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

-The number of turns on the coil

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

The direction of the force is reversed

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

The strength of the force is increased

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

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

What is the equation linking force, magnetic flux density, current and length?

F=BIL

Force (N)= Magnetic field strength (T) x Current (A) x length (m)

Explain electromagnetic induction.

When a wire cuts through magnetic field lines, a voltage is induced. if the wire is a complete circuit, current will be pushed around it.

How can the size of the induced voltage be increased?

- Increasing speed of movement

- Increasing the magnetic field strength

- Increasing the number of turns on the coil

Which rule is used for electromangetic induction?

Fleming's Right Hand Rule

Why is the current/voltage induced at a maximum when the coil is horizontal?

It cuts the most magnetic field lines per second.

What happens when the coil is vertical in an ac generator?

Current falls to 0

When is the voltage/current induced at its maximum?

180 degrees/horizontal

Increasing the speed of rotation of the coil increases the size of the output current and voltage. State one other effect increasing the speed of rotation has on the output.

Increased frequency

How does a transformer work?

1. An alternating voltage is passed through the primary coil which produces an alternating current in the primary coil

2. The current produces an alternating magnetic field in the iron core

3. Iron is a magnetic material, and so easily links this changing magnetic field to the secondary coil.

4. The alternating magnetic field in the secondary coil induces a voltage/current in the secondary coil

What equation is used to link the voltage and number of turns on the coils of a transformer?

V1/V2 =N1/N2

1= Primary coil

2= Secondary coil

How do you reduce heat loss within a transformer?

Laminate the iron core

Why is iron used in the core?

- It increases the strength of the magnetic field

- It magnetises and demagnetises quickly

State how the construction of a step-up is different to a step-down transformer.

Step-up: more coils/thicker wire in secondary coil

Step-down: less coils/thinner wire in secondary coil