Magnetism

Question 1

Units in magnetism (3)

Answer 1

units: ampere (A, current), volt (V, electric potential difference) and watt (W, power)

Question 2

What happens when 2 opposite poles get close?

Answer 2

They attract, North attracts South & South attracts North

Question 3

What happens when 2 same poles get close?

Answer 3

They repel each other

Question 4

Magnetically hard materials are materials that…

Answer 4

Dont lose their magnetism, they are permanent magnet materials

Question 5

Magnetically soft materials are materials that…

Answer 5

Lose their magnetismwhen they are no longer exposed to a magnetic field

Question 6

What is a magnetic field line

Answer 6

Around every magnet there is a region of space where we can detect magnetism (where magnetic materials will be affected). It always goes from North to South

Question 7

When is magnetism induced in some materials

Answer 7

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

Question 8

How do you produce a uniform magnetic field

Answer 8

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.H

Question 9

Does electric current in a conductor produces a magnetic field?

Answer 9

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

Question 10

describe the construction of electromagnets

Answer 10

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

Question 11

Explain why there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field

Answer 11

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 12

How does a motor work?

Answer 12

• 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 13

How does a Loudspeaker work?

Answer 13

• 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 14

In felmings left hand rule, what do the three fingers symbolise?

Answer 14

Thumb: Force
First finger: Magnetic Field
Second finger: Current

Question 15

How can we increase the force of the wire (direction & magnitude)

Answer 15

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 16

What happens when a conductor experiences a change in the magnetic field, potential difference or voltage?

Answer 16

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 17

How can we generate electricity?

Answer 17

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

Question 18

What factors affect the size of the induced voltage

Answer 18

· 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.

Question 19

describe the structure of a transformer, and its functions

Answer 19

AC current in the primary coil produces a changing magnetic field around the primary coil.

The iron core channels the changing field through the secondary coil.

The changing magnetic field induces a voltage in the secondary coil.

Question 20

Step Up and Step Down transformers:

Answer 20

Step Up transformers increase the voltage – more secondary turns than primary
Setep down transformers decrease the voltage – more primary turns than secondary

Question 21

know and use the relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer:

Answer 21

(input (primary) voltage / output(secondary)voltage) = (primary turns / secondary turns)