Magnetism and electromagnetism

Question 1

Current is measured in

Answer 1

amps (A)

Question 2

Potential Difference is measured in

Answer 2

volt (V)

Question 3

Power is measured in

Answer 3

watt (W)

Question 4

? poles attract and repel

Answer 4

Opposite poles attract and like charges repel

Question 5

Magnetically hard (permanent magnets)

Answer 5

Permanent magnets are made of magnetically hard materials such as steel. These materials retain their magnetism once magnetised.

Question 6

Soft magnets

Answer 6

Some materials like iron are magnetically soft. They lose their magnetism once they are no longer exposed to a magnetic field. They are used as temporary magnets such as electromagnets

Question 7

Magnetic field line

Answer 7

Around every magnet there is a region of space where we can detect magnetism (where magnetic materials will be affected).

This is called the magnetic field and in a diagram we represent this with magnetic field lines.

The magnetic field lines should always point from north to south.

Question 8

Temporary magnet

Answer 8

When magnetic materials are bought near or touch the pole of a strong or permanent magnet, they become magnets. This magnetic character is induced in the objects and it is removed when the permanent magnet is removed. This is a temporary magnet

Magnetism is induced in the paperclips so each paperclip can attract another one

Question 9

investigate the magnetic field pattern for a permanent bar magnet and between two bar magnets

Answer 9

Place your bar magnet in the centre of the next page and draw around it.
Place a compass at one pole of the bar magnet.
Draw a ‘dot’ to show there the compass is pointing,
Move the compass so the opposite end of the needle is pointing to the dot,
Repeat steps 3 and 4 until to reach the other pole of the magnet.
Do this procedure at least 5 times from different points on the pole of the magnet.
Tip, try to be as accurate as possible when drawing your dots
Join up your dots to create the field line plots

Question 10

how to use two permanent magnets to produce a uniform magnetic field pattern

Answer 10

A uniform magnetic field is comprised of straight, parallel lines which are evenly spaced. Between two opposite charges on flat magnets, a uniform magnetic field is formed.

Question 11

What produces a magnetic field?

Answer 11

A current travelling along a wire produces a circular magnetic field around the wire.

The magnetic field direction can be determined using the right hand grip rule.

Question 12

Construction of electromagnets

Answer 12

A soft iron core wrapped in wire. When current flows through the coil of wire it becomes magnetic.

Question 13

6.10

Answer 13

drawing

Question 14

Is there a force on a charged particle when it moves in a magnetic field?

Answer 14

The movement of the charged particle is a current so it produces a magnetic field. This magnetic field interacts with the permanent magnetic field to create a force. The force is perpendicular to the direction of motion and the permanent magnetic field.

Question 15

Why force is exerted in motors?

Answer 15

• Current flows in the wire/coil.
• This creates a magnetic field around the wire/coil.
• This magnetic field interacts with the field from the permanent magnet.
• This produces a force on the wire/coil which moves the wire/coil.
• The split-ring commutator changes the direction of the current every half turn as it spins. This reverses the direction of the forces, allowing the coil to continue spinning.

Question 16

Why force is exerted in loud speakers?

Answer 16

• An alternating current from the source passes though the coils in the speaker.
• This current is constantly changing direction and magnitude
• This current creates a magnetic field around the coil
• This field interacts with the magnetic field from the permanent magnets
• Creating a constantly changing force on the coil.
• This causes the coil to vibrate in and out as the direction of the force changes, moving the cone
• The cone causes vibrations which we hear as sound waves.

Question 17

Fleming’s left hand rule

Answer 17

Thumb: force

First finger: Magnetic Field

Second finger: Current

Question 18

how the force on a current-carrying conductor in a magnetic field changes with the magnitude and direction of the field and current

Answer 18

If you increase the magnitude of the current through a wire or the size of the magnet being used, you increase the force on the wire.

If you change the direction of the current or reverse the poles of the magnet, you change the direction of the force on the wire

Question 19

know that a voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it and describe the factors that affect the size of the induced voltage

Answer 19

When a conductor (can be a wire, coil or just a piece of metal) experiences a changing magnetic field a potential difference or voltage is induced in it. The strength of the potential difference depends on the strength of the magnetic field, how fast it changes i.e. how fast the coil is spinning, and how much of the conductor is exposed to the field i.e. how many turns in the coil.

Question 20

describe the generation of electricity by the rotation of a magnet within a coil of wire and of a coil of wire within a magnetic field

Answer 20

Electricity can be generated by either moving a magnet inside a coil of wire or rotating a coil inside a permanent magnetic field.

Model answer for a generator (Rotating coil):

· Coil is rotated within a magnetic field

· As it turns the coil cuts the magnetic field lines.

· This induces a voltage (or current) in the coil.

· This can then be connected to an existing circuit.

· In a generator, energy is being converted from kinetic (mechanical) energy into electrical energy.

· The size of the induced voltage (or current) can be increased by:

· Using a stronger magnet

· Having more turns in the coil

· Spinning/moving the coil faster.

Model answer for a generator (Rotating magnet)

· Magnet is rotated within a coil

· As it turns the coil cuts the constantly changing magnetic field lines from the magnet.

· This induces a voltage (or current) in the coil.

· This can then be connected to an existing circuit.

· In a generator, energy is being converted from kinetic (mechanical) energy into electrical energy.

· The size of the induced voltage (or current) can be increased by:

· Using a stronger magnet

· Having more turns in the coil

· Spinning/moving the magnet faster.