Section 6 - Magnetism and Electromagnetism

Question 1

What do magnets do to other magnets? *

Answer 1

Like poles repel and opposite poles attract

Magnetic materials can induce magnetism within objects that are made of magnetic materials, but don’t show properties of magnetism

Question 2

What are the properties of magnetically hard materials? *

Answer 2

They maintain their magnetic properties for a long period of time / permanently.

They are hard to demagnetise

Question 3

What are the properties of magnetically soft materials? *

Answer 3

It loses its magnetic properties as soon as it leaves a magnetic field

Question 4

What is a magnetic field line?

Answer 4

They are used to show the size and direction of magnetic fields. They always point form North to South

Question 5

How is magnetism induced in some materials when they are placed in a magnetic field? *

Answer 5

The magnetic field encourages the electrons of the non-magnetic material to align and form poles.

This can happen in iron, cobalt and nickel

Question 6

Describe experiments to investigate the magnetic field pattern for a permanent bar magnet and that between two bar magnets

Answer 6

You can use iron filings or multiple compasses to see the magnetic field lines coming out of a bar magnet or between two bar magnets

Question 7

How do you produce a uniform magnetic field line?

Answer 7

If you put two permanent bar magnets together with their north and south touching, then they will form the same magnetic field as if they were one bar magnet.

Question 8

What does an electric current in a conductor produce?

Answer 8

An electric current in a conductor produces a magnetic field around it. (Right Hand Rule)

Question 9

Describe the construction of electromagnets *

Answer 9

Wrap a piece of wire around a soft magnetic material.

When there is a current in the wire, a magnetic field is induced in the object.

Question 10

Sketch a magnetic field pattern for a straight wire when carrying a current *

Answer 10

a

Question 11

Sketch a magnetic field pattern for a flat circular coil when carrying a current *

Answer 11

a

Question 12

Sketch a magnetic field pattern for a solenoid when carrying a current *

Answer 12

a

Question 13

What happens to a charged particle when it moves in a magnetic field? *

Answer 13

If a charged particle moves through a magnetic field, it will experience a force. Unless it is parallel to the direction of the magnetic field, in which case it won’t experience a force.

Question 14

What happens when a current-carrying wire is put in a magnetic field?

Answer 14

A force is exerted

Fleming’s Left Hand Rule:

• Force is Thumb
• Field is Pointer Finger
• Current is Middle Finger

Question 15

Describe how simple d.c. electric motors work

Answer 15

In a d.c. motor, there is a wire in a magnetic field.
The force it experiences turns it around.
This turns the split ring commutator, which is where charge goes form the brushes into the wires

Question 16

Describe how a loud speaker works

Answer 16

A coil is in a magnetic field.
when a current rush through the wire, it will experience a force that pushes it away from the field.
this in turn pushes a cone which makes the sound.
Whatever frequency the AC current is at, the coil will move at that frequency, making a note of a certain pitch

Question 17

How can you increase the force on a current-carrying conductor in a magnetic field?

Answer 17

You can increase the strength of the field

You can increase the current

Question 18

How can you induce a voltage using a magnetic field? How can you change the voltage induced?

Answer 18

If you move a current-carrying wire back and forth across a magnetic field, a voltage will be induced

If you move a magnet back and forth through a coil of current-carrying wire, a voltage will be induced

If you increase the magnetic field strength, quicken the movement or increase the coils of wire, you can increase the voltage induced

Question 19

How can you induce a current using a magnetic field?

How can you reverse the direction of the induced current?

What factors would affect the size of the induced current?

Answer 19

If you move a magnet through a coil of wires (solenoid) a current can be induced.

You can reverse the magnet or its direction of movement

Speed of the magnet going through the coil
Magnetic field strength of the magnet
Number of turns in the coil

Question 20

Describe the structure of a transformer and how it performs its role? *

Answer 20

It will have a primary and secondary coil joined with an iron core.

When an alternating voltage is applied across the primary coil, the magnetically soft core magnetises and demagnetises quickly. This induces an alternating voltage in the secondary coil

Question 21

What is a step-up and step-down transformer and what is it used? *

Answer 21

Step-Up Transformers step the voltage up. They have more turns on the secondary coil than the primary coil

Step-Down Transformers step the voltage down. They have more turns on the primary coil than the secondary coil

Question 22

What is the relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer? *

Answer 22

Input (Primary) Voltage / Input (Secondary) Voltage is equal to Number of Turns on Primary / Number of Turns on Secondary

Question 23

Describe the relationship between input power and output power *

Answer 23

Input Power = Output Power