Section 5 - Current and Circuits

Question 1

What is current?

Answer 1

The flow of electric charge around the circuit

Question 2

What is the charge equation?

Answer 2

Charge = Current x Time
Coulombs = Amps x Seconds

Question 3

A battery passes a current of 0.25A through a light bulb over a period of 4 hours
How much charge does the battery transfer altogether?

Answer 3

Q = C x T
Q = 0.25 x 4(60x60)
Q = 3600C

Question 4

Calculate how long it takes a current of 2.5A to transfer a charge of 120C

Answer 4

Q = C x T
T = Q / C
T = 120 / 2.5
T = 48s

Question 5

What is potential difference?

Answer 5

The energy transferred per coulomb of charge

Question 6

What is the energy transferred equation?

Answer 6

Energy = Charge x Potential Difference
Joules = Coulombs x Volts

Question 7

What is the potential difference equation?

Answer 7

Voltage = Current x Resistance
Volts = Amps x Ohms

Question 8

A 4 ohm resistor in a circuit has a potential difference of 6.0 V across it
What is the current through the resistor?

Answer 8

V = I x R
I = V / R
I = 6 / 4
I = 1.5 A

Question 9

What does resisitance often cause?

Answer 9

An increase in temperature

Question 10

Why does resisitance increase heat?

Answer 10

When the electrons collide with the ions in the lattice that make up the resistor the ions gain energy which causes them to heat

Question 11

Give one exception where resistance decreases with heat?

Answer 11

Thermistor

Question 12

What usually happens when the resistor gets too hot?

Answer 12

No current will be able to flow

Question 13

A current flowing through a resistor transfer 360 J of energy when 75 C of charge are passed through it
Calculate the PD across the resistor

Answer 13

E = Q x V
V = E / Q
V = 360 / 75
V = 4.8 V

Question 14

What does a standard test circuit include?

Answer 14

Ammeter
Energy Source (eg. Battery)
Voltmeter
Component

Question 15

How do you use a standard test circuit?

Answer 15

Change the voltage and make readings from the ammeter and voltmeter and plot graph

Question 16

When testing the standard test circuit, what must you stop from happening?

Answer 16

The circuit getting too hot as it will affect results

Question 17

What does a diode do?

Answer 17

Acts as a one-way switch for the current

Question 18

What should you see when investigating thermistors?

Answer 18

As you heat the thermistor, the current through the thermistor increases as the resistance decreases

Question 19

What should you see when investigating LDR’s?

Answer 19

As the light gets brighter, the current increases as the resistance decreases

Question 20

Describe a resistor IV graph?

Answer 20

Directly proportional

Question 21

Describe a wire IV graph?

Answer 21

Directly proportional

Question 22

Describe a filament IV graph?

Answer 22

S shape

Question 23

Describe a diode IV graph?

Answer 23

Exponential in one direction (curver above x axis only)

Question 24

What are linear components?

Answer 24

Components that have an IV graph that’s a straight line

Question 25

What are non-linear components?

Answer 25

Components that have an IV graph that is curved

Question 26

How do LDRs affect resistance?

Answer 26

In bright light the resistance falls, in darkness the resistance is highest

Question 27

What are LDRs used in?

Answer 27

Automatic night lights Outdoor lighting Burgular detectors

Question 28

How do thermistors affect resistance?

Answer 28

In hot conditions the resistance drops, in cool conditions the resistance goes up

Question 29

What are thermistors used in?

Answer 29

Temperature detectors Car Engine sensors Thermostats

Question 30

Describe a series circuit?

Answer 30

A circuit of components connected in a line, end to end

Question 31

What is wrong with a series circuit?

Answer 31

IF you remove, break or disconnect one component the circuit will stop

Question 32

What are the rules behind a series circuit?

Answer 32

The current is the same everywhere The voltage is shared between the componenets The total resistance increases as you increase resistors

Question 33

Describe a parallel circuit?

Answer 33

A circuit of components where they are separately connect

Question 34

What are always connected in series?

Answer 34

Ammeters

Question 35

What are the rules behind a parallel circuit?

Answer 35

The voltage is the same across all components The current is shared between he branches The total resistance of the circuit decreases if you add a second resisitor in parallel

Question 36

A filament lamp and a resistor are connected in series A current of 0.5A flow through the lamp State the current flowing through the resisitor?

Answer 36

0.5 A

Question 37

What happens in series when you add resistors?

Answer 37

The total resistance increases

Question 38

Why does the resistance of a series circuit increase when you add resistors?

Answer 38

The voltage is being shared across more components, so there will be lower voltage through each resistor therefore the current will also be lower

Question 39

What happens in parallel when you add resistors?

Answer 39

The total resistance decreases

Question 40

Why does the resistance of a parallel circuit decrease when you add resistors?

Answer 40

Another loop will be added therefore the current will have an extra way to go which means the total current will increase therefore there will be a decrease in the total resistance

Question 41

A 12V cell is connected in series with a 2ohm resistor, a 3ohm resistor and a 7ohm resistor Calculate the current going through

Answer 41

``` V = I x R I = V / R I = 12 / (3+2+7) I = 12 / 12 ```

Question 42

What happens when an electrical charge goes through a change in potential difference?

Answer 42

Energy is transferred

Question 43

Why is energy transferred when a charge changes voltage?

Answer 43

Work is done against resistance

Question 44

What is the energy transferred equation?

Answer 44

``` E = I x V x t Energy = Current x Voltage x Time ```

Question 45

What do fuses do?

Answer 45

Protect the circuits by melting if the current gets too high

Question 46

How can heating from a circuit be good?

Answer 46

In toasters/bulbs/heaters, where a extremely resistant coil has electricity passed through it which gives off infrared radiation

Question 47

A laptop charger is connected to a 230 V source for an hour A current of 8.0 A flows through it Calculate the energy transferred by the laptop charger

Answer 47

``` E = I x V x t E = 8 x 230 x (60x60) E = 6,624,000 J ```

Question 48

What does energy transferred depend on?

Answer 48

How long the appliance is in for and its power

Question 49

What is the power equation?

Answer 49

Power = Energy / Time

Question 50

Which transfers more energy in the same time? A 500W microwave A 750W microwave

Answer 50

The 750W microwave

Question 51

What is the voltage of a charge?

Answer 51

The amount of energy each unit of charge transfers

Question 52

What is the power equation (IV)

Answer 52

``` P = I x V Power = Current x Voltage ```

Question 53

A 1 kW hair dryer is connected to a 230V supply | Find the fuse needed?

Answer 53

``` P = I x V P / V = I 1000 / 230 = I 4.3 A therefore a 5 A fuse is needed ```

Question 54

What is the power equation (IR)?

Answer 54

``` P = I² x R Power = Current² x Resistance ```

Question 55

Calculate the difference in the amount of energy transferred by a 250 W TV and 375 W TV when they are both use for two hours?

Answer 55

``` P = E / t 250 x (2x60x60) = E1 1,800,000 = E1 375 x (2x60x60) = E2 2,700,000 = E2 E2 - E1 = 900,000 ```

Question 56

What is AC?

Answer 56

Movement of charge in a constantly changing direction

Question 57

What produces alternating currents?

Answer 57

Alternating voltages

Question 58

What is the voltage inside the house?

Answer 58

230V

Question 59

What is the frequency of the house AC?

Answer 59

50Hz

Question 60

What supply direct current?

Answer 60

Batteries and cells

Question 61

What creates DC?

Answer 61

Direct Voltage

Question 62

What colour is the live wire?

Answer 62

Brown

Question 63

What is the live wire

Answer 63

The wire that carries the voltage

Question 64

What colour is the neutral?

Answer 64

Blue

Question 65

What is the neutral wire?

Answer 65

The wire that completes the circuit

Question 66

What is the voltage of the blue wire?

Answer 66

0V

Question 67

When does the blue wire have a current?

Answer 67

When the appliance is working normally

Question 68

What colour is the earth wire?

Answer 68

Green and yellow

Question 69

What is the earth wire?

Answer 69

The wire for safety and protection | It carries the current away if something goes wrong

Question 70

What is the voltage of the earth wire?

Answer 70

0V

Question 71

What is the voltage of the live wire?

Answer 71

230V

Question 72

Explain the difference between a.c and d.c electricity supplies?

Answer 72

In AC the movement of the charges constantly changes whilst in a direct current supply the movement of the charges is only in one direction

Question 73

What do earthing and fuses prevent?

Answer 73

Electrical overloads

Question 74

What can current surges lead to?

Answer 74

Melting, fire or electric shocks

Question 75

What is a fault?

Answer 75

Where the live wire touches the metal case

Question 76

What do circuit breakers do?

Answer 76

Instead of melting, a large current simply shuts it off

Question 77

What are the advantages of circuit breakers?

Answer 77

Can be reused and much quicker than fuses

Question 78

What are the disadvantages of circuit breakers?

Answer 78

Expensive

Question 79

What doesn't need an earth wire?

Answer 79

A double insulated appliance

Question 80

Which wire are fuses connect to?

Answer 80

The Live wire

Question 81

Name one linear component and one non-linear component?

Answer 81

Resistor and diode

Question 82

What happens to the resistance of a thermistor as it gets hotter?

Answer 82

It decreases

Question 83

How does the current in each component differ?

Answer 83

Based off the resistance in the components

Question 84

How does potential difference vary in parallel?

Answer 84

Total amount shared inside each branch

Question 85

How does adding resistors in parallel affect the resisitance?

Answer 85

It decreases it

Question 86

Give two disadvantages of the heating effect?

Answer 86

Inefficient and can break circuit

Question 87

Give two advantages of the heating effect?

Answer 87

Can be made into useful energy (bulb or heater) and can be used in fuse

Question 88

What is a power rating

Answer 88

The power that flows through the componenet

Question 89

Why are the three wires in a three-core cable coloured?

Answer 89

Avoid confusion which could lead to shocks

Question 90

Give the potential difference for the three wires?

Answer 90

Live - 230 V Neutral - 0 V Earthed - 0 V

Question 91

Explain why touching a live wire is dangerous?

Answer 91

The wire has 230 V which will flow through you to reach earth

Question 92

Explain how a fuse works?

Answer 92

If the current gets too hot, the temperature will increase and melt the fuse, stopping the circuit from working