Electricity

Question 1

currents in a series circuit:
potential difference in a series circuit:

Answer 1

• are the same
• splits between components

Question 2

current in parallel circuits:
potential difference in parallel circuits:

Answer 2

• splits between components
• current in the branches adds up to the total current leaving the cell
• the same

Question 3

how do we measure current?

Answer 3

using an ammeter

Question 4

how do we measure potential difference?

Answer 4

using a voltmeter

Question 5

define resistance

Answer 5

tells us the potential difference required to drive a current through a component

Question 6

what are the properties of a resistor? (2)

Answer 6

• current through a resistor is directly proportional to the potential difference
• this is called an ohmic conductor
• the resistance will only stay constant if the temperature is constant

Question 7

what is the resistance of a filament lamp?

Answer 7

• the current through a filament lamp is inversely proportional to the potential difference
• this is because the filament gets hot and that causes the resistance to increase

Question 8

why does resistance increase in a filament lamp at higher temperatures?

Answer 8

• the atoms in the filament vibrate more
• the electrons in the current now collide more with the atoms
• more energy is needed to push the current through the filament lamp

Question 9

properties of a diode? (2)

Answer 9

• the current through the diode flows in one direction only
• the diode has a very high resistance in the reverse direction

Question 10

what are diodes useful for?

Answer 10

controlling the flow of current in circuits

Question 11

properties of LED’s? (3)

Answer 11

• the current flows in one direction only
• gives off light when the current flows through
• energy efficient

Question 12

resistors in series circuits…

Answer 12

add together

Question 13

resistors in parallel circuits…

Answer 13

the total resistance of the two resistors is less than the resistance of the smallest individual resistor

Question 14

properties of an LDR?

Answer 14

• in dark conditions, the resistance is high
• in light conditions, the resistance is low

Question 15

what is a thermistor?

Answer 15

the resistance of a thermistor decreases if the temperature increases

Question 16

what is DC supply?

Answer 16

’direct current’
- the current from a cell

Question 17

what is AC supply?

Answer 17

’alternating current
- mains electricity in the UK
- current constantly changing direction

Question 18

what are the properties of AC supply in the UK? (2)

Answer 18

in the UK…

• AC has a frequency of 50 hertz
• AC has a potential difference of around 230 volts

Question 19

what are the three cores of a three core cable?

Answer 19

1. Brown
2. Blue
3. Green/Yellow striped wire

Question 20

what is the brown wire of a three core cable?

Answer 20

LIVE
- carries the alternating potential difference from the supply (around 230 volts)
- connected to a fuse in the plug

Question 21

what is the blue wire of a three core cable?

Answer 21

NEUTRAL
- completes the circuit
- potential difference = 0 volts

Question 22

what is the green/yellow striped wire of a three core cable?

Answer 22

EARTH
- safety wire to stop the appliance from becoming live

Question 23

what is the national grid?

Answer 23

a system of transformers and high voltage cables

Question 24

what is a step-up transformer?

Answer 24

• increases the potential difference to several hundred thousand volts
• less energy is lost in the power cables when the potential difference is very high

Question 25

what is a step-down transformer?

Answer 25

• decreases the potential difference to around 230 volts so that the potential difference isn’t too high when passed to the homes