Electricity

Question 1

What is the symbol for a thermistor?

Answer 1

Question 2

What is the symbol for a diode?

Answer 2

Question 3

What is the size of current?

Answer 3

The flow of electrical charge. The size of current is the rate of flow of electrical charge

Question 4

In a series circuit, what is true of current?

Answer 4

There is the same current through each component

Question 5

What is potential difference?

Answer 5

The push that drives the flow of electrical current - a measure of the energy given to the charge carriers in a circuit.

Question 6

What is an ohmic conductor?

Answer 6

A conductor that follows Ohm’s law, maintaining a constant resistance over wide range of voltages

Question 7

Describe the IV graph of an ohmic conductor (at a constant temperature)

Answer 7

Current across ohmic conductor is directly proportional to the potential difference, meaning resistance remains constant as current changes (constant temp)

Question 8

Which components do not have a constant resistance?

Answer 8

e.g. lamps, diodes, thermistors, LDRs (resistance changes with current)

Question 9

Explain this graph

Answer 9

The resistance of a filament lamp increases as the temperature of the filament increases

Question 10

Explain this graph

Answer 10

The current through the diode flows in one direction because the diode has a very high resistance in the reverse direction

Question 11

What happens with thermistors when temperature increases?

Answer 11

Thermistor’s resistance DECREASES as temp INCREASES

Question 12

What is an application of a thermistor in a circuit

Answer 12

Being a thermostat

Question 13

How does LDR change with light intensity?

Answer 13

The resistance of an LDRs DECREASES as light intensity INCREASES

Question 14

What is an application of an LDR in circuits?

Answer 14

e.g. switching lights on hen it gets dark

Question 15

What is true of series circuits with potential difference?

Answer 15

Total potential difference of the power supply is shared between the components

Question 16

What is true of series circuits with resistance?

Answer 16

Resistance of two components is the sum of the resistance of each component

Question 17

What is true of parallel circuits with potential difference?

Answer 17

Same across each component in the circuit

Question 18

What is true of parallel circuits with current?

Answer 18

Total current through the whole circuit is the sum of the currents through the separate components

Question 19

What is true of parallel circuits with resistance?

Answer 19

Total resistance is less than the resistance of the smallest individual resistor

Question 20

Why does resistance add up in a series circuit?

Answer 20

In series, current has to pass through each component one after the other. So resistance adds up, making it harder for current to flow, so total resistance increases

Question 21

Why does resistance add up in a parallel circuit?

Answer 21

When adding more resistors in parallel, current can split and flow through multiple paths at the same time. Current has more than one route so flows through easier, so overall resistance decreases

Question 22

Why use DC circuit for measuring and testing purposes?

Answer 22

• Same current through all components so can observe how current is affected and therefore resistance
• Steady unidirectional flow allows accurate measurements + is predictable
• If it was AC, readings would fluctuate and be harder to interpret

Question 23

Explain the difference between direct and alternating p.d.

Answer 23

DC: voltage stays the same and flows in one direction only
AC: Voltage changes size and direction constantly

Question 24

What is the frequency and voltage of the domestic electricity supply in the UK?

Answer 24

50 Hz
230V

Question 25

What are the 3 colours of the insulation layer of wires in electrical appliances?

Answer 25

Live wire - brown Earth wire - yellow and green stripes Neutral wire - blue

Question 26

What does each wire in a 3-core cable do?

Answer 26

Live wire carries the alternating potential difference from the supply Neutral wire just completes the circuit Earth wire is a safety wire to stop the appliance becoming live

Question 27

The potential difference between the live wire and earth?

Answer 27

230V

Question 28

What are the neutral and earth wires' p.d

Answer 28

Neutral at or close to 0V (earth potential) - earth wire at 0V (only carries current if there is a fault in the circuit)

Question 29

What are the dangers of providing connection between the live wire and earth wire?

Answer 29

If live wire accidentally touches the earth wire, it creates a short circuit, causing a very large current to flow. This can damage wiring and cause electric shock If wires get too hot, could start a fire

Question 30

Why might a live wire may be dangerous even when a switch in the mains circuit is open?

Answer 30

Live wire can still be dangerous as it may be connected to power supply before the switch in the circuit. So it could still have a high voltage and cause an electric shock if touched

Question 31

Why does power = IV

Answer 31

Multiplying voltage (energy per coulomb) by current (coulombs per second) gets you power - the total energy transferred every second. The higher the current or p.d. , the higher the power output

Question 32

The amount of energy an appliance transfers depends on what?

Answer 32

How long the appliance is on for and the power of the appliance

Question 33

When is work done in a circuit?

Answer 33

When charge flows through a circuit

Question 34

What does the power rating of a domestic appliance say?

Answer 34

The power rating tells you how much energy it transfers every second it is switched on. Appliances with a higher power rating can cause a change in stored energy faster

Question 35

Examples of appliances with high and low power ratings

Answer 35

High: kettles, microwave ovens Low: LED lights, phone chargers

Question 36

How is electrical power transferred from power stations to consumers?

Answer 36

the National Grid

Question 37

What are step-up and step-down transformers used for on the National Grid?

Answer 37

Step up: increase the p.d. from the power station to the transmission cables Step down: decrease p.d. to much lower value for domestic use

Question 38

Why is the National Grid an efficient way to transfer energy?

Answer 38

- Uses very high voltages to transfer electrical energy over long distances - High voltage means current can be low for same power - Lower current reduces energy lost as heat in the wires - So is more efficient as less wasted energy

Question 39

When certain insulating materials rub against each other what happens?

Answer 39

The become electrically charged as negatively charged electrons rub off one material and onto the other. (Materials are left with equal but opposite charge as same number of electrons are lost or gained). This is the production of static electricity

Question 40

How does sparking occur?

Answer 40

Friction when rubbing surfaces causes electrons to be transferred from one material to the other, creating build-up of static electricity. When difference in charge is large enough, electrons randomly jump across the gap - a spark

Question 41

What is the evidence that charged objects exert forces upon each other?

Answer 41

When oppositely charged surfaces are brought close enough together, it can be observed that they move towards each other unprompted. Similarly charged objects are observed to repel each other and push apart without contact. This shows that electrical forces are non-contact

Question 42

How do electric fields explain the non-contact force between charged objects?

Answer 42

-An electric field is the region around a charged object where other charged objects eel a force - This shows how charge influences the space around it, meaning repulsion or attraction can be experienced from a distance - When electric field is very strong, electrons jump across gap (sparking)