Magnetism and electromagnetism.

Question 1

What are two types of magnetic poles?

Answer 1

A north and a south pole.

Question 2

Where is the magnetic field the strongest?

Answer 2

At the poles.

Question 3

Permanent magnet.

Answer 3

A permanent magnet produces its own magnetic field.

Question 4

Induced magnet.

Answer 4

Becomes a magnet when in a magnetic field. Induced magnetism always causes a force of attraction. When removed from the magnetic field an induced magnet loses most/all of its magnetism quickly.

Question 5

What is the magnetic field?

Answer 5

The region around a magnet where a force acts on another magnet or on a magnetic material (iron, steel, cobalt and nickel) .

Question 6

What is the direction of a magnetic field line?

Answer 6

From the north (seeking) pole of a magnet to the south(seeking) pole of the magnet.

Question 7

What is flux density?

Answer 7

It is the density of the field lines. The closer the lines, the higher the density, the stronger the fields.

Question 8

What does a magnetic compass contain and what does it tell us?

Answer 8

contains a small bar magnet. The compass needle points in the direction of the Earth’s magnetic field. Provides evidence that the Earth’s core is magnetic.

Question 9

How can a magnetic compass be used to plot the field around a bar magnet.

Answer 9

1) Place the bar on the paper.
2) Compass at one end of the bar.
3) On the paper mark where the needle points.
4) Move the compass to the tail of the needle where it was marked.
5) Mark the next point.
6) Repeat and connect the marks until the full field is plotted.

Question 10

When a current flows through a conducting wire what is produced around the wire?

Answer 10

A magnetic field.

Question 11

. The strength of the magnetic field depends on what?

Answer 11

The current through the wire and the distance from the
wire.

Question 12

What is a solenoid?

Answer 12

A coil of conducting wire.

Question 13

Describe the steps of the right-hand grip method which can tell us the direction of the current.

Answer 13

-Grip the wire in your right hand with the thumb pointing in the direction of the current.
-The fingers curled around the wire will point in the direction that the field lines should be drawn.
Current goes from negative to positive going downwards.

Question 14

What is an electromagnet?

Answer 14

An electromagnet is a solenoid with an iron core.

Question 15

Describe how an electric bell works.

Answer 15

1)Switch is pushed the electromagnet is magnetised.
2) The electromagnet attracts the armature.
3) The hammer strikes the gong and breaks the circuit.
4) The armature springs back, completing the circuit again and remagnetising the electromagnet.
5) The cycle repeats for as long as the button is pushed.

Question 16

What is the motor effect?

Answer 16

When a conductor carrying a current is placed in a magnetic field the magnet producing the field and the conductor exert a force on each other.

Question 17

How can force be increased?

Answer 17

By increasing either:
-Size of the current.
-The length of the conductor in the magnetic field
-The flux density.

Question 18

Force equation.

Answer 18

Magnetic flux density * current * length (of wire within the field)

Question 19

Flemmings left-hand rule.

Answer 19

Hold your thumb, forefinger and second finger at right angles to each other: the forefinger is pointed in the direction of the magnetic field lines - from north to south; the second finger is pointed in the direction the current flows; the thumb shows the direction of the force on the conductor carrying the current.

Question 20

What is the basis of an electric motor?

Answer 20

A current-carrying coil in a magnetic field will rotate. One side moves up and one side moves down.

Question 21

Electric motors- When the brush contacts at the commutator what does It ensure?

Answer 21

It ensures that the current direction in the coil is always in the same direction. Ensures the motor doesn’t stop and continues rotating.

Question 22

How can you make a motor faster?

Answer 22

increase the current or magnetic field.

Question 23

What is the generator effect?

Answer 23

When conductors and magnetic fields interact a potential difference can be induced (creating electricity).

Question 24

How can the potential difference be induced?

Answer 24

By an electrical conductor moving relative to a magnetic field.
- A change in the magnetic field around a conductor.

Question 25

What does an induced current generate?

Answer 25

It generates a magnetic field that opposes the original change which produces it.

Question 26

What is the generator effect used in?

Answer 26

Alternators-To generate alternating current.
Dynamos-To generate direct current

Question 27

What happens in an alternator?

Answer 27

A rotating magnet is used with a fixed coil of wire. It rotates and the direction of the field which passes alternates. Induces alternating potential/current.

Question 28

What happens in a dynamo?

Answer 28

The coil rotates and the magnet is fixed. Coil rotates and generates potential difference in one direction.

Question 29

What is the use of the split-ring commutator?

Answer 29

it means that once the coil has passed the upright position the connections are reversed, As a result, the direction of current output is always in the same direction.

Question 29

When is the induced potential at 0?

Answer 29

When the coil and field are at right angles and the field lines are being cut.

Question 30

When is potential difference greatest in alternators and dynamos?

Answer 30

When the coil and magnetic field are parallel, so the magnetic field is being cut by the rotating coil at the fastest rate.

Question 31

Which effect and current is used in loudspeakers?

Answer 31

Motor effect. Alternating current.

Question 32

How are sound waves in a speaker produced?

Answer 32

a current in the coil creates a magnetic field
- field interacts with the permanent magnet generating a force, pushes cone outwards
- current made to flow in the opposite direction
-direction magnetic field reverses
the force on the cone- pulls it back in repeatedly alternating the current direction making the cone vibrate in and out
-cone vibrations cause pressure variations in the air - which are sound waves.

Question 33

Does a large cone give high or low-pitched sounds?

Answer 33

Low-pitched sounds.

Question 34

Which effect and current is used in microphones?

Answer 34

alternating current. Microphones use the generator effect to convert the pressure variations in sound waves.

Question 35

How are sound waves produced in a microphone?

Answer 35

1) Sound waves hit the microphone.
2) Changes in air pressure related to sound waves cause the diaphragm to oscillate.
3) Diaphragm/coil vibrates at the same frequency as the incoming sound wave-equal.
4) Induces a potential difference and current in the coil with the same frequency as the incoming sound wave.

Question 36

What does a basic transformer consist of?

Answer 36

a primary coil and a secondary coil wound on an iron core.
Iron is used as it is easily magnetised.

Question 37

How does a transformer function?

Answer 37

1) An alternating current flows through the primary coil- a solenoid
2) Alternating current induces an alternating magnetic field.
3) Field in the iron core induces an alternating potential difference in the 2nd coil.
4) If the secondary coil is part of a full circuit an AC flows in the secondary coil.

Question 38

What is the function of a microphone?

Answer 38

A microphone converts sound waves into electrical signals and loudspeakers do the opposite.