P4 - Magnetism and Magnetic Fields

Question 1

What is a magnetic field?

Answer 1

Where a magnetic material experiences a force

Question 2

What is a magnet?

Answer 2

A magnet is any material or object that produces a magnetic field.

Question 3

How can the strength of the magnetic field be shown by?

Answer 3

The strength of a magnetic field is shown by the density of the magnetic field lines.

Question 4

What can the magnetic field lines show?

Answer 4

• The direction that a small compass would point at that point
• The strength of the magnet at a particular point
• Whether two magnets would attract or repel

Question 5

Name the different ways to see magnetic field patterns.

Answer 5

• Use iron filings

- Use a compass to plot the magnetic fields

Question 6

Which elements are magnetic?

Answer 6

• Iron
• Nickel
• Cobalt

Question 7

What does a current carrying wire have?

Answer 7

A magnetic field around it.

Question 8

How can you show the magnetic field direction on a current carrying wire?

Answer 8

• Plotting compasses

- Right hand grip rule

Question 9

The further away you go from the wire what happens to the magnetic field?

Answer 9

It gets weaker

Question 10

How can you increase the magnetic field around a solenoid?

Answer 10

• Increasing the current
• Increasing the number of turns of coils
• Decreasing the cross-sectional area of the solenoid
• When an iron core is added inside the solenoid

Question 11

What is a solenoid?

Answer 11

Lots of coils of wire together.

Question 12

What is the generator effect?

Answer 12

When you move an current carrying wire in a magnetic field, a potential difference is induced.

Question 13

How can a wire experience a full force?

Answer 13

The wire has to be at 90˚ to the magnetic field

Question 14

What happens to the force if the current or the magnetic field is stronger?

Answer 14

The force is stronger

Question 15

How can you show the direction of a force on a current carrying conductor?

Answer 15

Using the Fleming’s Left Hand rule

Question 16

What is Fleming’s Left Hand rule?

Answer 16

The thumb is the direction of the force
The first finger is the direction of the magnetic field from north to south
The second finger is the direction of current

Question 17

How can you calculate the force acting on a current carrying wire?

Answer 17

Force on a conductor carrying a current (N) = magnetic flux density (Tesla) x current (A) x length (m)

Question 18

How does a d.c motor/ simple electric motor work?

Answer 18

• A current carrying coil sits between two opposite poles of a magnet
• Since there is a current flowing in different direction on each side of a coil, and it is perpendicular to the magnetic field, each side will experience forces in opposite directions.
• Since the coil is on a spindle it rotates
• The split-ring commutator swaps the positive and negative connections every half turn. So the direction of the current reverses every half turn so the forces will always be on the same direction

Question 19

How does a loudspeaker work?

Answer 19

• There is a solenoid with a magnet in it and it is surrounded by another magnet.
• A.c electrical signals are given to the coil of wire which is wrapped around the base of a cone.
• This causes a magnetic field and it forces it to move in one direction.
• As it is alternating current the current changes direction making the coil go backwards.
• This continues to happen making the cone vibrating causing sound to be transmitted

Question 20

What is electromagnetic induction?

Answer 20

When a potential difference is induced across a conductor which is experiencing a change in its external magnetic field.

Question 21

What are the two ways you can get an electromagnetic induction

Answer 21

• The electrical conductor and a magnetic field move relative to each other
• The magnetic field through an electrical conductor gets bigger or smaller or reverses direction

Question 22

How does an alternator work with a rotating magnet??

Answer 22

• A magnet rotates in a coil of wire.
• The magnet spins causing an alternating p.d being induced across the end of the coil. The p.d changes direction every half turn because the field changes

Question 23

How does an alternator work with a rotating coil?

Answer 23

• The current carrying wire induces a magnetic field causing a force against the wire.
• As it moves and when the coil is parallel to the magnets the slip rings at the the end of the coil remain in contact with the carbon brushes which is connected to the rest of the circuit.
• This causes no current to flow every half turn making it produce a.c

Question 24

How does a microphone work?

Answer 24

• The person creates sound waves
• The sound waves strike the diaphragm
• As the diaphragm moves the coil of wire also moves inducing a p.d across the ends of the coil of wire.

Question 25

What is a step down transformer?

Answer 25

• They have more turns on the primary coil than the secondary coil.
• They step down the voltage

Question 26

What is a step-up transformer?

Answer 26

• They step up the voltage

- They have more turns on the secondary coil than the primary coil

Question 27

What is the transformer equation?

Answer 27

p.d across the primary coil ÷ p.d across secondary coil = number of turns in primary coil ÷ number of turns in secondary coil