1
Q
CIRCUIT SYMBOLS
A
Cell
A single source of electrical energy.
2
Q
CIRCUIT SYMBOLS
A
Battery
Two or more cells together supplying electrical energy.
3
Q
CIRCUIT SYMBOLS
A
Switch open
A switch that breaks the circuit, so current does not flow.
4
Q
CIRCUIT SYMBOLS
A
Switch closed
A switch that completes the circuit, so current can flow.
5
Q
CIRCUIT SYMBOLS
A
Fuse
A safety device that melts and breaks the circuit if current gets too high.
6
Q
CIRCUIT SYMBOLS
A
Filament lamp (bulb)
A lamp that lights when current flows through it.
7
Q
CIRCUIT SYMBOLS
A
LED
Light Emitting Diode — gives out light when current flows in the correct direction.
8
Q
CIRCUIT SYMBOLS
A
Resistor
A component that reduces or limits the flow of current.
9
Q
CIRCUIT SYMBOLS
A
Variable resistor
A resistor whose resistance can be changed.
10
Q
CIRCUIT SYMBOLS
A
Ammeter
A meter used to measure current.
11
Q
CIRCUIT SYMBOLS
A
Voltmeter
A meter used to measure potential difference (voltage).
12
Q
CIRCUIT SYMBOLS
A
Diode
A component that allows current to flow in one direction only.
13
Q
CIRCUIT SYMBOLS
A
LDR
Light Dependent Resistor — its resistance changes with light intensity.
14
Q
CIRCUIT SYMBOLS
A
Thermistor
A resistor whose resistance changes with temperature.
15
Q
CURRENT
What is electric current?
A
Electric current is a flow of electrical charge.
16
Q
CURRENT
When will electric charge flow around a circuit?
A
It will only flow around a complete (closed) circuit if there is a potential difference.
17
Q
CURRENT
What is the unit of current?
A
The ampere (A).
18
Q
CURRENT
What kind of loop has the same current everywhere?
A
A single, closed loop.
19
Q
CURRENT
What is potential difference also called?
A
Voltage.
20
Q
CURRENT
What does potential difference do?
A
It is the driving force that pushes charge round the circuit.
21
Q
CURRENT
What is the unit of potential difference?
A
The volt (V).
22
Q
CURRENT
What is resistance?
A
Anything that slows the flow down.
23
Q
CURRENT
What is the unit of resistance?
A
The ohm (Ω).
24
Q
CURRENT
What does the current through a component depend on?
A
The potential difference across it and the resistance of the component.
25
**CURRENT**
What happens to current when resistance increases?
The current gets smaller.
26
**CURRENT**
What does total charge through a circuit depend on?
Current and time.
27
**CURRENT**
What is current the rate of flow of?
Charge.
28
**CURRENT**
What does the formula Q = It mean?
Charge = current × time.
29
**CURRENT**
What are the units in Q = It?
Q is in coulombs (C), I is in amps (A), and t is in seconds (s).
30
**CURRENT**
What happens when a larger current flows?
More charge passes around the circuit.
31
**CURRENT**
What should wires look like in a circuit diagram?
They should be straight lines.
32
**CURRENT**
What must be true for a circuit diagram to be closed?
You must be able to follow a wire from one end of the power supply, through the components, to the other end.
33
**RESISTANCE AND V=IR**
What is the formula linking potential difference, current and resistance?
V = I × R
34
**RESISTANCE AND V=IR**
What does I stand for?
Current
35
**RESISTANCE AND V=IR**
What does V stand for?
Potential difference
36
**RESISTANCE AND V=IR**
What does R stand for?
Resistance
37
**RESISTANCE AND V=IR**
What is the unit of potential difference?
Volts (V)
38
**RESISTANCE AND V=IR**
What is the unit of resistance?
Ohms (Ω)
39
**RESISTANCE AND V=IR**
What is the unit of current?
Amps (A)
40
**RESISTANCE AND V=IR**
How do you find current from V = IR?
I = V ÷ R
41
**RESISTANCE AND V=IR**
How do you find resistance from V = IR?
R = V ÷ I
42
**RESISTANCE AND V=IR**
A resistor has a potential difference of 6.0 V and a resistance of 4.0 Ω. What is the current?
1.5 A
43
**RESISTANCE AND V=IR**
What can affect the resistance of a circuit?
Whether components are in series or parallel, and the length of wire used.
44
**RESISTANCE AND V=IR**
What does an ammeter measure?
Current
45
**RESISTANCE AND V=IR**
How must an ammeter be placed in a circuit?
In series
46
**RESISTANCE AND V=IR**
What does a voltmeter measure?
Potential difference (pd)
47
**RESISTANCE AND V=IR**
How must a voltmeter be placed in a circuit?
In parallel
48
**Resistance and I-V Characteristics**
What does an I-V characteristic show?
It shows how current changes as potential difference changes.
49
**Resistance and I-V Characteristics**
What does I stand for on an I-V graph?
Current.
50
**Resistance and I-V Characteristics**
What does V stand for on an I-V graph?
Potential difference.
51
**Resistance and I-V Characteristics**
What is an ohmic conductor?
A component like a wire or resistor that has a constant resistance at a constant temperature.
52
**Resistance and I-V Characteristics**
How does current behave in an ohmic conductor at constant temperature?
Current is directly proportional to potential difference.
53
**Resistance and I-V Characteristics**
What shape is the I-V graph for an ohmic conductor?
A straight line through the origin.
54
**Resistance and I-V Characteristics**
What happens to the resistance of an ohmic conductor as current changes?
It stays constant, as long as the temperature stays constant.
55
**Resistance and I-V Characteristics**
Why is a fixed resistor called a linear component?
Because it has a straight-line I-V characteristic.
56
**Resistance and I-V Characteristics**
What is a non-linear component?
A component whose I-V graph is curved rather than straight.
57
**Resistance and I-V Characteristics**
What happens in a filament lamp when current flows?
The filament heats up and transfers energy to thermal energy.
58
**Resistance and I-V Characteristics**
What happens to the resistance of a filament lamp as temperature increases?
Its resistance increases.
59
**Resistance and I-V Characteristics**
What happens to current in a filament lamp as resistance increases?
Current increases more slowly, so the graph becomes shallower.
60
**Resistance and I-V Characteristics**
What shape is the I-V graph for a filament lamp?
A curved graph.
61
**Resistance and I-V Characteristics**
Why does the filament lamp graph become less steep?
Because the filament gets hotter, so resistance increases.
62
**Resistance and I-V Characteristics**
What is special about a diode?
It allows current to flow in one direction only.
63
**Resistance and I-V Characteristics**
What happens if the current is reversed in a diode?
The diode has very high resistance and little or no current flows.
64
**Resistance and I-V Characteristics**
What shape is the I-V graph for a diode?
A curved graph that rises steeply in the forward direction and is almost flat in reverse.
65
**Resistance and I-V Characteristics**
What does very high resistance mean for a diode in reverse bias?
It stops current flowing.
66
**Resistance and I-V Characteristics**
What is meant by forward direction in a diode?
The direction in which current is allowed to flow.
67
**Resistance and I-V Characteristics**
What is meant by reverse direction in a diode?
The direction in which the diode resists current flow.
68
**Circuit devices**
What does LDR stand for?
Light Dependent Resistor.
69
**Circuit devices**
What happens to the resistance of an LDR in bright light?
The resistance falls.
70
**Circuit devices**
What happens to the resistance of an LDR in darkness?
The resistance is highest.
71
**Circuit devices**
What does the resistance of an LDR depend on?
Light intensity.
72
**Circuit devices**
What are LDRs used for?
They are used in circuits that sense changes in light levels.
73
**Circuit devices**
Give examples of LDR uses.
Automatic night lights, outdoor lighting, and burglar detectors.
74
**Circuit devices**
What is a thermistor?
A temperature-dependent resistor.
75
**Circuit devices**
What happens to the resistance of a thermistor in hot conditions?
The resistance drops.
76
**Circuit devices**
What happens to the resistance of a thermistor in cool conditions?
The resistance goes up.
77
**Circuit devices**
What does the resistance of a thermistor depend on?
Temperature.
78
**Circuit devices**
What are thermistors used for?
They are used as temperature detectors.
79
**Circuit devices**
Give examples of thermistor uses.
Car engine temperature sensors and electronic thermostats.
80
**Circuit devices**
What is a sensing circuit?
A circuit used to turn on or increase power to a component depending on the conditions.
81
**Circuit devices**
What two components are used in the sensing circuits shown?
A thermistor or an LDR with a fixed resistor.
82
**Circuit devices**
Why do the fixed resistor and the fan always have the same potential difference across them in the first circuit?
Because they are connected in parallel.
83
**Circuit devices**
How is the potential difference shared in a sensing circuit?
It is shared between the thermistor and the loop made up of the fixed resistor and fan according to their resistances.
84
**Circuit devices**
What happens to the share of potential difference taken by a bigger resistance?
It takes more of the potential difference.
85
**Circuit devices**
What happens in the fan circuit as the room gets hotter?
The thermistor’s resistance decreases, so the pd across the fixed resistor and fan rises, making the fan go faster.
86
**Circuit devices**
What happens if you connect a component across a variable resistor instead?
The pd across the component changes as the variable resistor changes.
87
**Circuit devices**
What happens to a bulb connected in parallel with an LDR when it gets dark?
The bulb gets brighter.
88
**Circuit devices**
Why does a bulb connected across an LDR get brighter in the dark?
Because the LDR’s resistance is high in the dark, so the pd across both the LDR and bulb is high.
89
**Circuit devices**
What happens to the energy transferred to a component when the pd across it is greater?
The component gets more energy.
90
10. Physics (AQA Combined Science)
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