magnetism + electromagnetism

Question 1

In induced Magnete, what do the materials not have?

Answer 1

Fixed poles.

Question 2

How can materials be made into temporary magnets?

Answer 2

By being ‘stroked’ with a permanent magnet.

Question 3

How does stroking a material with a permanent magnet make it a temporary magnet?

Answer 3

As it aligns the domains in the material in all the same direction.

Question 4

What does current produce around a wire?

Answer 4

A magnetic field.

Question 5

What rule determines the direction of current?

Answer 5

The right hand grip rule.

Question 6

Which finger points in the direction of the current in the ‘right hand grip rule’?

Answer 6

Thumb.

Question 7

What does every other finger in the ‘right hand grip rule’ represent?

Answer 7

The direction of the field.

Question 8

The greater the current…

Answer 8

The stronger the magnetic field.

Question 9

The greater the distance from the wire…

Answer 9

The weaker the field.

Question 10

Coiling the wire in a solenoid causes…

Answer 10

The field to align and form one giant field.

Question 11

Why does the iron core in the centre of the solenoid increase its strength?

Answer 11

As it is easier for magnetic field lines to pass through in comparison to air.

Question 12

What are 5 factors that affect strength?

Answer 12

~Size of current
~Length
~Cross sectional area
~Number of coils
~Soft iron core

Question 13

In the motor effect, a magnet and a wire will also exert a force as…

Answer 13

The two magnetic fields generated by the magnet and the current in the wire interact.

Question 14

What shape is the magnetic field around a wire?

Answer 14

Circular.

Question 15

What shape is the magnetic field between two magnets?

Answer 15

Straight.

Question 16

How does the conventional current move in Fleming’s left hand rule?

Answer 16

Moves in the opposite direction to the electrons.

Question 17

How do you calculate force using magnetic flux density?

Answer 17

Force = magnetic flux density x current x length

Question 18

What is magnetic flux density measured in?

Answer 18

Tesla and is the number of flux lines per metre squared.

Question 19

How do permanent magnets lie in electric motors?

Answer 19

In fixed positions.

Question 20

What is between the permanent magnets in an electric motor?

Answer 20

A coil of current carrying wire lies on an axis.

Question 21

Why does an electric motor rotate?

Answer 21

Force on one side moves that side up and force on the other side (where current flows in the opposite direction) moves down.

Question 22

When is a potential difference induced across the conductor?

Answer 22

When there is a relative movement between a conductor and a magnetic field.

Question 23

A current flows if the conductor forms…

Answer 23

A complete circuit.

Question 24

When the current prod yes its own magnetic field, it opposes…

Answer 24

The change inducing it.

Question 25

When the turbine spins in an electric generator, the movement causes…

Answer 25

The wire to cut through the magnetic field and creates a potential difference.

Question 26

When does an AC flow in an electrical generator?

Answer 26

When the coil of wire is connected to a complete circuit.

Question 27

When is a DC produced in an electric generator?

Answer 27

If the ends are connected to a split ring commutator.

Question 28

What does a split ring commutator reverse and why?

Answer 28

The current each half - rotation so the current remains positive (dynamo system).

Question 29

What is produced when the cone moves in a loudspeaker?

Answer 29

Pressure variations which make sound.

Question 30

What interacts in loudspeakers causing the coil to move?

Answer 30

The magnetic fields from the current and the magnet.

Question 31

What is the current produced in dynamic microphones proportional to?

Answer 31

The sound signal.

Question 32

What is at the centre of a dynamic microphone?

Answer 32

A fixed magnet with a coil of wire around it that is free to move.

Question 33

Pressure variations in sound waves in dynamic microphones cause…

Answer 33

The coil to move and current is induced as it moves.

Question 34

More coils on the secondary in transformers means…

Answer 34

It is a step up transformer as voltage will increase as the changing field will cut through more of the secondary wire inducing a larger potential difference.

Question 35

Fewer coils on the secondary in transformers means…

Answer 35

It is a step down transformer as a smaller potential difference forms.

Question 36

Number of coils on primary ——————————————- = Number of coils on secondary

Answer 36

Pd of primary ——————— Pd of secondary