Magnetism And Electromagnetism

Question 1

The microphone is used to convert the pressure variations in sound waves into variations in ______

Answer 1

Current.

Question 2

What material is used in the core of a transformer?

Answer 2

Iron, because it is easily magnetised

Question 3

Why do we use iron as the core in a transformer?

Answer 3

Because it is easily magnetised.

Question 4

What is a solenoid?

Answer 4

A long insulated coil of wire.

Question 5

List some of the magnetic metals.

Answer 5

Iron, cobalt, nickel.

Question 6

What is induced magnetism?

Answer 6

When an object becomes magnetic when it is placed in a magnetic field.

Question 7

How is induced magnetism lost?

Answer 7

When the magnet moves out of the magnetic field.

Question 8

Where is the magnetic force of a magnet at its strongest?

Answer 8

Near its poles.

Question 9

What is the direction of magnetic field lines?

Answer 9

North to South

Question 10

What type of force is magnetism?

Answer 10

Non-contact.

Question 11

How can you show that an object is a permanent magnet?

Answer 11

By checking if it repels another magnet.

Question 12

What equipment do you need to draw out magnetic field lines?

Answer 12

A bar magnet, a plotting compass, paper and a pencil.

Question 13

The closer the field lines, the __ the magnetic field.

Answer 13

Stronger.

Question 14

What is Fleming’s left hand rule?

Answer 14

-Thumb shows direction of Force
-First finger shows direction of Magnetic Field
-Second finger shows direction of Electrical Current

Question 15

What strengthens the magnetic field of a wire?

Answer 15

-Increasing current of the wire.

Question 16

What is an electromagnet?

Answer 16

A solenoid with an iron core.

Question 17

What is the motor effect?

Answer 17

Where a force is exerted on a current-carrying wire due to the presence of a magnetic field.

Question 18

What increases induced potential difference in a generator?

Answer 18

-Increasing the speed of movement
-Increasing the magnetic field strength
-Increasing the number of turns on the coil.

Question 19

What is a transformer?

Answer 19

A device that can change the potential difference or voltage of an alternating current.

Question 20

The higher the current in a cable, the greater the what?

Answer 20

The greater the energy transferred to the surroundings by heating.

Question 21

How does the National Grid reduce energy transfers to the environment?

Answer 21

Uses transformers to increase the voltage and lower the current when travelling through transmission cables.

Question 22

How does a transformer work? (8 steps)

Answer 22

An alternating current flows in the primary coil.
This creates a magnetic field that is changing in strength and direction.
This field interacts with the secondary coil.
The secondary coil experiences a change in magnetic field.
The coil “cuts” through magnetic field lines.
This induces a potential difference.
If there is a complete circuit, a current is also induced.
If there are more turns on the secondary coil than the primary, the voltage is “stepped up”.

Question 23

Explain how a microphone works. (6 steps)

Answer 23

Sound waves vibrate the diaphragm.
The diaphragm moves the coil.
The coil experiences a change in magnetic field.
The coil “cuts” through magnetic field lines.
This induces a potential difference.
If there is a complete circuit, a current is also induced.

Question 24

Explain how a generator works. (5 steps)

Answer 24

A coil is moved in a magnetic field.
The coil experiences a change in magnetic field.
The coil “cuts” through magnetic field lines.
This induces a potential difference.
If there is a complete circuit, then a current is also induced.

Question 25

Explain how a speaker works. (6 steps)

Answer 25

A current passes through the coil.
This current creates a magnetic field.
This magnetic field interacts with the magnetic field formed by the permanent magnet.
This causes a force on the coil.
The current is alternating and changes direction, which changes the direction of the magnetic field and therefore the force.
The changing force vibrates the cone, which causes air particles to vibrate and creates sound.

Question 26

Explain how a motor works. (6 steps)

Answer 26

A current passes through the coil.
This current creates a magnetic field.
This magnetic field interacts with the magnetic field formed by the permanent magnet.
This causes a force on the coil.
The force causes the coil to rotate.
The split ring commutator reverses the current every half turn to keep the coil spinning in the same direction.