Topic 10 - Circuits

Question 1

What does AC mean?

Answer 1

Alternating current

Question 2

What does DC mean?

Answer 2

Direct current

Question 3

Is mains electricity AC or DC?

Answer 3

AC

Question 4

What is meant by the frequency of a supply?

Answer 4

The rate at which an AC current changes

Question 5

What is the frequency and voltage of the UK mains electricity supple?

Answer 5

Frequency = 50Hz
Voltage = 230V

Question 6

What type of current do batteries and cells supply?

Answer 6

Direct current (DC

Question 7

What is the power rating of an appliance?

Answer 7

It shows how much energy a device converts per second

Question 8

What wires does a typical domestic appliance have?

Answer 8

Live wire
Neutral wire
Earth wire

Question 9

What colour is the live wire?

Answer 9

Brown

Question 10

What colour is the neutral wire?

Answer 10

Blue

Question 11

What colour is the earth wire?

Answer 11

Green and yellow (striped)

Question 12

Explain when the earth wire does and doesn’t carry a current

Answer 12

Under normal circumstances, no current flows through the earth wire
Current flows when a fault occurs in the appliance (such as a surge or the casing becoming live)

Question 13

What potential is the neutral wire at?

Answer 13

0 volts

Question 14

State the potential difference between the live and earth wires

Answer 14

230 volts

Question 15

What is the purpose of the neutral wire?

Answer 15

The complete the circuit by connecting the appliance back to the mains supply

Question 16

For metal appliances, where is the the earth wire connected to? Why?

Answer 16

The metal casing of the appliance

If the live wire becomes touching the casing, the current will flow through the earth wire, preventing electrocution

Question 17

How does a fuse stop a device from getting damaged?

Answer 17

When the current becomes too high the fuse wire will melt and break, therefore stopping current from flowing to the appliance and preventing damage

Question 18

Why is it important to connect a fuse or switch to the live wire?

Answer 18

When the switch is turned off, or when the fuse breaks, it will break the circuit and stop current running through the wire. This provides a method to stop current flowing into the appliance

Question 19

Why is it dangerous to have a connection between the earth wire and the live wire?

Answer 19

It can result in a current surge, causing electrical shocks

Question 20

What factors affect the energy transferred when charge flows through a component?

Answer 20

Amount of charge

The potential difference across the component

Question 21

How do you work out energy?

Answer 21

Current x potential difference x time

Question 22

Define potential difference in terms of charge

Answer 22

The work done per unit charge

Question 23

How to work out energy transferred

Answer 23

Charge x potential difference

Question 24

When an electrical current flows through a resistor why does it heat up?

Answer 24

There are collisions between the electrons and the ions in the resistor’s lattice. This causes a transfer of kinetic energy into thermal energy which is released into the surroundings

Question 25

How do low resistance wires reduce unwanted energy transfers?

Answer 25

A smaller resistance will mean there are fewer collisions, therefore less energy will be wasted through heating

Question 26

What are some advantages of the heating effect in resistors?

Answer 26

It is useful for appliances such as toasters or electrical fires, where the heat is the desired product

Question 27

What are some disadvantages of the heating effect in resistors?

Answer 27

The loss of energy as it can make an appliance inefficient | If an appliance overheats it can catch fire or overhear, which could ruin the device or injure the user

Question 28

What are the units of power?

Answer 28

Watts (W)

Question 29

Define power

Answer 29

The rate of energy transfer or the rate at which work is done

Question 30

How do you work out power (in circuit)?

Answer 30

``` Current x potential difference OR Current^2 x resistance OR Energy/time ```

Question 31

How does resistance affect current in a circuit?

Answer 31

As the total resistance of a circuit increases, the current flowing through the circuit decreases

Question 32

How can’t he current in a circuit be varied?

Answer 32

Using a variable resistor

Question 33

How do you calculate potential difference?

Answer 33

Current x resistance | Energy transferred/charge

Question 34

How is total resistance affected by two resistors in series?

Answer 34

The total resistance is equal to the sum of the two resistors

Question 35

How is total resistance affected by two resistors in parallel?

Answer 35

The total resistance decreases; it is less than the resistance of the resistor with the lowest resistance

Question 36

What is an ohmic conductor ? State the condition required

Answer 36

A conductor for which current and potential difference are directly proportional Resistance remains constant as current changes Temperature must be constant

Question 37

List 4 components for which resistance is not constant as current changes

Answer 37

Filament lamps Diodes Thermistors Light dependant resistors

Question 38

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

Answer 38

Resistance increases Metal ions have more kinetic energy so vibrate more, colliding more frequently with electrons as they flow through the metal This created more resistance to current flow

Question 39

What is different about current flow through a diode?

Answer 39

The current only flows in one direction | Resistance is very high in the other direction, preventing current flow

Question 40

State what happens to the resistor of a thermistor as temperature increases?

Answer 40

It decreases

Question 41

Give two examples of when a thermistor may be used

Answer 41

In a thermostat to turn a heater on below a certain temperature In a freezer to turn on a cooler when the temperature becomes too high

Question 42

State what happens to the resistance of an LDR as light intensity decreases

Answer 42

It increases

Question 43

Give an application for a LDR

Answer 43

Street lamps or night lights

Question 44

How do diodes work?

Answer 44

It only allows current to flow in one direction. If current is flowing the right way, the resistance is large for small voltages, but then at higher voltages becomes very small

Question 45

What are the two ways that a component can be connected in a circuit?

Answer 45

Series or parallel

Question 46

What is voltage also know as?

Answer 46

Potential difference

Question 47

How does the potential difference across two components vary when connected in series and parallel?

Answer 47

In a series circuit the total potential difference is shared between each component In a parallel circuit the potential difference across each component is the same

Question 48

If two resistors are connected in parallel, what can be said about their combined total resistance?

Answer 48

Their total resistance is less than the smallest of the two individual resistances

Question 49

If two resistors are connected in series what can be said about their total resistance?

Answer 49

Their total combined resistance is equal to the sum of the two individual resistances

Question 50

Where must a voltmeter be placed in a circuit?

Answer 50

In parallel with the component that is being measured

Question 51

How can a volt be described?

Answer 51

Joule per coulomb

Question 52

What is an electric current?

Answer 52

The rate of flow of charge

Question 53

How to work out charge

Answer 53

Current x time

Question 54

What can be said about the value of current at any point in a single closed loop?

Answer 54

Current is the same in all points in a closed loop

Question 55

What two factors does the current in a circuit depend on?

Answer 55

Potential difference | Resistance

Question 56

What is an ammeter and where must it be connected in a circuit?

Answer 56

An ammeter measures current . It is placed in series with the component it is required to measure

Question 57

What happens when current reaches a junction in a circuit?

Answer 57

Current is conserved; the total current remains the same and is split between the two branches

Question 58

What three subatomic components make up an atom?

Answer 58

Electrons Protons Neutrons

Question 59

How is current defined?

Answer 59

The rate of flow of charge (or electrons) around a circuit

Question 60

What are the units of charge?

Answer 60

Coulombs (C)