P2

Question 1

What must be included in a circuit for current to flow?

Answer 1

a source of potential difference

Question 2

What is current?

Answer 2

the flow of electrical charge

Question 3

equation linking charge flow, current & time?

Answer 3

charge flow(Q) = current(I) x time(t)

Question 4

What is charge measured in?

Answer 4

coulombs

Question 5

What happens when a component has a greater resistance?

Answer 5

It has a smaller current

Question 6

equation that links potential difference, current and resistance?

Answer 6

potential difference(V) = current(I) x resistance(R)

Question 7

What factors affect the resistance of an electrical circuit?

Answer 7

• length of wire( at a constant temp)
• combination of resistors in series and parallel

Question 8

What does a resistor do?

Answer 8

oppose the flow of electric current through the circuit

Question 9

What is ohms law?

Answer 9

the voltage across a conductor is directly proportional to the current flowing through as long as all physical conditions remain constant

Question 10

Describe the current, potential difference and resistance through an ohmic conductor

Answer 10

• the current through an ohmic conductor (at a constant temp) is directly proportional to the potential difference across the resistor
• the resistance remains constant as the current changes

Question 11

Give examples of non-ohmic conductors?

Answer 11

• filament lamp
• diode

Question 12

What happens to the the resistance of a filament lamp as the temperature increase?

Answer 12

the resistance increases

Question 13

What happens to the resistance of an LDR as light intensity increases?

Answer 13

the resistance decreases

Question 14

Give a use of an LDR

Answer 14

light sensing circuits e.g. street lamps

Question 15

Describe the current in a diode

Answer 15

the current flows in one direction only and the resistance is very high in the reverse direction

Question 16

What happens to the resistance of a thermistor as the temperature increases?

Answer 16

the resistance decreases

Question 17

Give a use of a thermistor

Answer 17

a sensor circuit of a thermostat

Question 18

What is a series circuit?

Answer 18

A circuit that has all its components connected in one single loop

Question 19

What is a parallel circuit?

Answer 19

A circuit where components are connected on separate branches of wire to the energy source

Question 20

Describe the current, potential difference and resistance in series circuit

Answer 20

• the same current flows through each component (I1=I2=I3 etc…)
• the the total potential difference is shared between the components (Vtotal= V1+V2 etc…)
• the total resistance is the sum of the resistance of each component (Rtotal= R1+R2 etc…)

Question 21

Describe the current, potential difference and resistance in a parallel circuit

Answer 21

• the total current is the sum across separate components
• the potential difference is the same across all components
• the total resistance is smaller than the resistance of the smallest resistor

Question 22

What is an equivalent resistor?

Answer 22

In a series circuit, when two resistors are connected they can be replaced by one equivalent resistor which has a resistance equal to the sum of the ones being replaced

Question 23

What will happen to a bulb that is connected in series with a thermistor, as the temperature on the thermistor changes?

Answer 23

• at high temperatures, the bulb grows brighter
• at high temperatures, there is a higher potential difference across the bulb

Question 24

What is Mains electricity in the UK?

Answer 24

an alternating current supply with a frequency of 50Hz and voltage of 230V

Question 25

What is the difference between direct and alternating current?

Answer 25

Alternating current constantly changes direction and is used in mains electricity whilst direct current always flows in the same direction and is used in solar cells & batteries

Question 26

What does an oscilloscope screen show?

Answer 26

Voltage against time

Question 27

What are different colours in the three-core cable?

Answer 27

**Neutral wire** -blue = completes the circuit and carries current way from the appliance - close to earth potential difference= 0v **Earth wire** - yellow/green = a safety wire to stop the appliance becoming live and only carries a current if there is a fault - has a 0v potential **Live wire** -brown = provides the alternating potential difference from the mains electricity supply - carries a 230v potential difference

Question 28

What is a fuse?

Answer 28

a safety measure that involves a thin wire that melts if the current flowing through an appliance is too high. This breaks the current and stops the flow of current

Question 29

What is a circuit breaker?

Answer 29

A special device that switches off the flow of current if the current is higher than a certain value. They do the same job as fuses but can be used multiple times

Question 30

What are the three available fuse ratings?

Answer 30

3A, 5A and 13A

Question 31

Why do metal cases need earthing?

Answer 31

If there is a fault in the appliance and one of them touches the case due to metals being conductors, anyone touching the case could receive an electric shock

Question 32

Why can the live wire and earth wire never be in contact?

Answer 32

This would remove the safety feature of the earth wire

Question 33

What happens if you touch the live wire?

Answer 33

Your body would supply a link between the supply and the ground and cause an electric shock

Question 34

What is the National Grid?

Answer 34

A system of cables and transformers that connects power stations to consumers

Question 35

Explain the function of a step-up transformer

Answer 35

A step-up transformer has more turns on the secondary coil so the voltage increases

Question 36

Explain the function of a step-down transformer

Answer 36

A step-down transformer has fewer turns on the secondary coil so the voltage decreases

Question 37

How can static electricity be produced?

Answer 37

through friction- by rubbing two electrical insulators against one another - one would lose electrons- become positive - the other would gain these electrons- become negative

Question 38

Can a static charge build up on a conductor?

Answer 38

yes- if the conductor is isolated

Question 39

What is a spark?

Answer 39

when an electrical charge builds up on an object the potential difference between the object and earth increases, if the potential difference is large enough the electrons can jump across the gap and produces a spark

Question 40

What do charged objects create around them?

Answer 40

Electrical fields

Question 41

Describe what may effect the strength of an electric field

Answer 41

- the closer an object is to the charged object, the stronger the electric field - the higher the charge of the object, the stronger the electric field