P7-Magnetism and Electromagnetism

Question 1

What makes an object magnetic?

Answer 1

The domains can line up-the molecules’s electrons spin in the same direction

Question 2

What poles attract?
What poles repel?

Answer 2

• Opposite
• Same

Question 3

What are the magnetic materials?

Answer 3

Iron, Cobalt and Nickel

Question 4

What is a magnetic field?

Answer 4

The region around a magnet

Question 5

What is a permanent magnet?

Answer 5

A magnet that always produces a magnetic field and can’t be turned on or off

Question 6

What is an induced magnet?

Answer 6

A magnet that can be magnetised when placed in another magnetic field

Question 7

What are the characteristics of magnetic field lines?

Answer 7

• Travel from north to south poles
• Are more concentrated at the poles than elsewhere
• Never cross-only loop around
• Form rings

Question 8

What direction does a current flowing through a wire produce its own magnetic field when veiwed from the direction the current is flowing and what tells us that the current is facing that direction on a diagram?

Answer 8

• Clockwise
• A cross

Question 9

What direction does a current flowing through a wire produce its own magnetic field when veiwed from the the direction the current isn’t flowing and what tells us that the current is facing that direction on a diagram?

Answer 9

• Anti-Clockwise
• A dot

Question 10

What direction does a current flowing through a wire produce its own magnetic field?

Answer 10

Clockwise-right hand rule

Question 11

What is a solenoid and what does it produce?

Answer 11

A long coil of insulating wire-it produces a magnetic field

Question 12

What is an electromagnet?

Answer 12

A soleniod with an iron core

Question 13

What increases the strength of an electromagnet?

Answer 13

• Increasing the current
• Increasing the number of coils

Question 14

What is the motor effect?

Answer 14

A wire carrying a current that creates a magnetic field that interacts with another magnet to cause a force that pushes the wire at right angles

Question 15

How can the size of the motor effect force be increased?

Answer 15

• By increasing the current
• By using a stronger magnet
• By increasing the length of the wire

Question 16

How do you use Fleming’s left hand rule?

Answer 16

Thumb-Force
1st finger-Magnetic field
2nd finger-Current

Question 17

What is the formula for force on a wire in a magnetic field?

Answer 17

Force = magnetic flux density x current x length
F = BIL

Question 18

What are the units for magnetic flux density?

Answer 18

tesla, T

Question 19

What is magnetic flux density?

Answer 19

The strength of the magnetic field

Question 20

What causes the motor to keep spinning in the motor effect?

Answer 20

A split-ring commutator

Question 21

What current is used in an electric motor?

Answer 21

Direct current

Question 22

What can cause a current to be generated and what is this called?

Answer 22

A coil of wire being moved in relation to a magnet-this creates an induced current-called the generator effect.

Question 23

What factors reverse the current generated from a magnet?

Answer 23

If the magnet is moved back out of the coil
If the other pole of the magnet is moved into the coil

Question 24

How does an AC generator work?

Answer 24

A coil is rotated in the magnetic field inducing a current and brushes making contact between this wire and an external circuit causes an alternating current to flow in the external circuit

Question 25

How can the maximum current be increased in an AC generator?

Answer 25

* Increasing the rate of rotation * Increasing the strength of the magnetic field * Increasing the number of turns on the coil

Question 26

How is a DC current produced by a generator? What is the name for this generator?

Answer 26

* By having a split ring commutator-however this produces a 'lumpy' current * Dynamo

Question 27

What do transformers do?

Answer 27

* The increase the size of the voltage of an alternating current (step up transformer) while reducing the current) * They decrease the size of the voltage of an alternating current (step down transformer) while increasing the current)

Question 28

What causes a step up transformer?

Answer 28

If there are more turns in the secondary coil

Question 29

How do transformers work?

Answer 29

* An AC power supply is supplied to the primary coil-this produces a magnet field that changes as the current changes * The iron core increases the strength of the magnetic field * The changing magnetic field induces a changing potential different in the secondary coil * The induced potential difference produces an alternating current in the electric circuit