Paper 2 Knowledge Gaps: Content

Question 1

What are the different types of generators?

Answer 1

• alternators
• dynamos

Question 2

What current does an alternator produce?

Answer 2

Alternating current

Question 3

What current does a dynamo produce?

Answer 3

Direct Current

Question 4

What is the difference between the parts of an alternator and the parts of a dynamo?

Answer 4

• alternators have slip rings and brushes
• dynamos have split ring commutators

Question 5

Describe how an alternator works

Answer 5

• The coil of wire rotates relative to the magnets,
• this induces a magnetic field in the coil
• which then induces a voltage and current in the coil.
• as the coil rotates faster, the peaks of the oscillation get larger and more frequent

Question 6

What is the role of a slip ring in an alternator?

Answer 6

• the contacts don’t swap every half turn
• so an alternating current is produced

Question 7

How do dynamos work?

Answer 7

• As the coil of wire spins relative to the magnet, a magnetic field is induced
• so, a voltage and current are induced in the coil.
• as the coil rotates faster, the oscillations get larger and more frequent

Question 8

What is the role of the split ring commutator in a dynamo?

Answer 8

• contacts swap every half turn
• so the current is always flowing in the same direction
• producing a direct current

Question 9

What do loudspeakers do?

Answer 9

Take electrical signals and use the motor effect to convert them into vibrations, which then generate sound waves

Question 10

What do microphones do?

Answer 10

Detect vibrations caused by sound waves and convert them into electrical signals

Question 11

What current do loudspeakers and microphones use?

Answer 11

alternating current

Question 12

What effect do loudspeakers and microphones use?

Answer 12

Motor effect

Question 13

How does a loudspeaker work?

Answer 13

1. A.C. flows through wire and creates a magnetic field
2. this magnetic field of the coil interacts with the magnetic field of the permanent magnet in the loudspeaker
3. interacting magnetic fields exert a force onto the coil and cause it to move back and forth
4. the cone will change shape
5. as current is alternating, the magnetic field and the force experienced is also alternating, so the coil of wire and cone rapidly vibrate
6. vibrations are so fast that the cone vibrations cause pressure variations in the air - sound waves are produced

Question 14

How does a microphone work?

Answer 14

1. sound waves hit the diaphragm
2. diaphragm and coil of wire move
3. wire is moving within the magnetic field of the permanent magnet = current generated

Question 15

What determines the frequency and amplitude of the current produced in a sound wave?

Answer 15

the frequency and amplitude of sound waves

Question 16

Describe the process that electricity goes through in the national grid?

Answer 16

1. generated at power stations
2. goes through a step up transformer
3. goes through a bunch of wires and plyons
4. goes to step down transformer
5. then travels to our homes

Question 17

Why are step up transformers used in the national grid?

Answer 17

• it increases the voltage to 400,000V
• and minimises energy loss

Question 18

What is the role of step down transformers in the national grid?

Answer 18

• decreases voltage to 230V

Question 19

Describe how transformers work

Answer 19

1. alternating potential difference is applied across the primary coil
2. causes a current to flow
3. causing a magnetic field around the coil
4. this induces a magnetic field in the iron core
5. which induces a potential difference in the secondary coil
6. which produces an alternating current

Question 20

Define moment

Answer 20

Rotational or turning effect of a force

Question 21

What is the equation for moment?

Answer 21

force x perpendicular distance from the pivot

Question 22

What are the units for moment?

Answer 22

Nm (Newton metres)