Electricity

Question 1

Current

Answer 1

The rate of flow of electrical charge

Question 2

What does current depend on

Answer 2

• resistance -> greater the resistance the smaller the current
• potential difference -> greater the pd the greater the current

Question 3

Explain the current in an ohmic conductor

Answer 3

It is directly proportional to the potential difference across the resistor

-> this means that / is because of the resistance remains constant as the current changes

Question 4

What happens to the resistance in a filament lamp

Answer 4

It increases as the temperature increases

Question 5

Describe the current and resistance in a diode

Answer 5

• the current only flows in one direction
• it has very high resistance in the reverse direction

Question 6

What happens to the resistance of a thermistor when temperature increses

Answer 6

It decreases

Question 7

What happens to the resistance of an LDR when light instensity increases

Answer 7

It decreases

Question 8

Application of thermistors

Answer 8

It is a temperature sensor regularly used as a thermostat -> this means it automatically regulates temperature or active a device when the temperature reaches a certain point

Question 9

State Ohm’s law

Answer 9

The current through a conductor is directly proportional to the potential difference across it as long as temperature is constant

Question 10

For components in a series circuit:

Answer 10

• there is the same current through each component
• the total pd of the power supply is shared between the components
• the total resistance of 2 components is the sum of the resistance of each component
  -> R(total) = R1 + R2

Question 11

For components connected in a parallel circuit:

Answer 11

• the pd across each component is the same
• the total current through the whole circuit is the sum of the currents through the separate components
• the total resistance of 2 resistors is less than the resistance of the smallest individual resistor

Question 12

Why does adding resistors in series increase resistance

Answer 12

Because the current is the same in every component, so the more resistors we add, the harder it is for current to flow and overall resistance increases

Question 13

Why does adding resistors in parallel decrease resistance

Answer 13

The more resistors we add the more pathways the current has to go through so it is easier for current to flow, decreasing resistance

Question 14

Frequency of UK mains supply

Answer 14

50Hz

Question 15

Voltage of UK mains supply

Answer 15

230V

Question 16

Difference between direct and alternating potential difference

Answer 16

Direct produced a constant electric current that flows in one direction, whilst alternating produces an alternating current that changes direction regularly

Question 17

How are appliances connected to the mains

Answer 17

Using a three-core cable

Question 18

Name the different wires’ colours

Answer 18

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

Question 19

Role of the live wire

Answer 19

Carries the alternating potential difference from the supply

Question 20

Role of the neutral wire

Answer 20

Completes the circuit

Question 21

Role of the earth wire

Answer 21

Stops the appliance becoming live

Question 22

The dangers of providing connection between the live and earth wires

Answer 22

It would make a complete circuit from the mains supply to the ground and a shock or fire would likely occur

Question 23

Why is a live wire dangerous even if the switch is open (ie circuit is switched off)

Answer 23

Because touching it can complete the circuit between the live wire and the earth (as you’re standing on the floor) causing a shock

Question 24

Explain the relationship of power with current and pd

Answer 24

If current or pd increases the power increases (ie the rate of energy transfer increases)

Question 25

National Grid

Answer 25

A system of cables and transformers linking power stations to consumers

Question 26

Step-up transformers

Answer 26

Used to increase the pd so that current decrease and resistance also decreases in the wires reducing the energy lost to the surroundings

Question 27

Step down transformers

Answer 27

Decrease voltage so that it is safe to use in homes

Question 28

Static charge

Answer 28

- when certain insulating materials are rubbed against each other they become electrically charged - negatively charged electrons are rubbed off one material and on to the other -> the material that gains electrons becomes negatively charged and the material that loses electrons has a positive charge

Question 29

Explain how sparks occur

Answer 29

- when 2 objects have a strong electric field between them, electrons in the air molecules will be strongly attracted to the positively charged object - if the electric field is strong enough, electrons will be pulled away from the air molecules and cause a flow of electrons between the 2 objects -> this is a spark

Question 30

Explain the concept of an electric field

Answer 30

Area surrounding an electric charge that may influence other charged particles

Question 31

How does the concept of an electric field help explain the non-contact force between charged objects

Answer 31

The objects don’t need to touch, but do need to be within each others electric fields

Question 32

Where are the ammeter and voltmeter placed in relation to a circuit

Answer 32

Ammeter is in series with the circuit Voltmeter is in parallel

Question 33

How does a thermostat reduce temp

Answer 33

if it gets too hot, the thermistor will have lower resistance, allowing more current to flow to potentially cool the room

Question 34

What is a resistor

Answer 34

an electrical component that is used to control the flow of electric current in a circuit

Question 35

How does a resistor work

Answer 35

by converting electrical energy into heat energy, which reduces the flow of current in a circuit

Question 36

What factors affect resistance

Answer 36

- length of wire -> - thickness - material - temp

Question 37

Potential difference

Answer 37

energy transferred ,per unit of charge, between two points in a circuit

Question 38

Resistance

Answer 38

opposition to the flow of current