1
Q
What makes a complete circuit in terms of charge?
A
Connection from positive to negative
2
Q
What is electric charge?
A
Flow of electric charge
3
Q
What is the symbol of electric charge?
A
Q
4
Q
What is electric charge measured in?
A
Coulombs C
5
Q
What is charge carried around by in an electrical circuit?
A
Delocalised electrons
6
Q
What is electric current?
A
Rate of flow of charge
7
Q
What is electric current measured in?
A
Amperes (Amps) A
8
Q
What is electric current measured by?
A
Ammeter connected in series
9
Q
What is the equation involving current?
A
Current = Charge moved / Time
A = C/t
10
Q
What is the potential difference?
A
Energy gained or lost by each coulomb of charge
11
Q
What is the symbol for potential difference?
A
Pd
12
Q
What is potential difference measured in?
A
Volts
13
Q
What is potential difference measured by and how?
A
A voltmeter in parallel across components. (Not part of the actual circuit)
14
Q
Before and after a component, the charge had different levels of …
A
Electric potential energy
15
Q
What carries electric potential energy around the circuit?
A
Charge
16
Q
What transfers energy TO the charge?
A
Batteries, cells and power supplies
17
Q
What transfers energy FROM the charge?
A
Other components such as bulbs, bells etc.
18
Q
What is the equation involving potential difference, energy and charge?
A
Potential difference = Energy / Charge
V = E/Q
19
Q
What is the equation for resistance?
A
Resistance = Potential difference / Current
^ = V/ A
20
Q
What is resistance measured in?
A
Ohms ^
21
Q
What can the size of the current be affected by?
A
Increasing or decreasing the voltage or resistance
22
Q
The higher the resistance …
A
The less current
23
Q
All wires and components …. current.
A
Resist
24
Q
Good electrical conductors have … resistance
A
Low
25
Poor electrical conductors have … resistance.
High
26
What causes resistance?
Collisions with positive ions in wires
27
What is the effect of resistance?
Collisions limit current, causing friction and causing the wire to heat up
28
What does the resistor do in an electrical circuit?
Restricts or limits flow of electric current
29
What does the LDR do in an electrical circuit?
Light sensor- resistance changes due to light intensity
30
What does the thermistor do in an electrical circuit?
Temperature sensor- controls resistance
31
What does the diode do in an electrical circuit?
One way valve for current
32
What does the switch do in an electrical circuit?
Breaks or closes an electrical circuit
33
What does the cell do in an electrical circuit?
Provides electrical power by converting chemical energy to electric energy
34
What does the bulb do in an electrical circuit?
Converts electrical to light energy
35
What does the variable resistor do in an electrical circuit?
Controls and changes resistance
36
What does the LED do in an electrical circuit?
Produces light efficiently
37
What does the ammeter do in an electrical circuit?
Measures the electrical current
38
What does the voltmeter do in an electrical circuit?
Measures the potential difference
39
What does the fuse do in an electrical circuit?
Breaks current flow when it exceeds a safe level
40
Resistance =
Potential difference (V) / current (A)
41
How is the size of current affected?
By increasing or decreasing the voltage of resistance
More resistance means less current
42
What do all wires and components do in a circuit?
Resist current
43
Good electrical conductors have … resistance
Low
44
Good insulators have … resistance
High
45
Causes of resistance in wires
Collisions with ions in wires
46
Effects of resistance in wires
Collisions limit current, causing friction and the wire heats up
47
What is resistance measured in?
Ohms
48
What is ohms law?
The current through a component is directly proportional to the PD across it, providing the temperature is constant
Resistance is constant
49
Voltage =
Current x resistance
50
Gradient of a VI graph
Resistance, higher resistance, steeper gradient
51
What happens to current in a series circuit?
It is the same everywhere
52
What happens to voltage in a series circuit?
Supply voltage is shared by individual components
53
What happens to voltage in a parallel circuit?
Voltage is the same as the supply across every branch
54
What happens in a series circuit if one component fails?
Entire circuit fails
55
What happens in a parallel circuit if one component fails?
The entire circuit continues
56
In a parallel circuit: The total current flowing into a junction =
Total flowing out
57
Information about series circuits:
Current is the same everywhere
Voltage of components adds up to voltage of battery
Total resistance is sum of all component resistances
58
Information about parallel circuits:
Current into junction = current out
Voltage in each branch is same as battery
Total resistance decreases with each branch added
59
What do ohmic resistors have?
Constant resistance
60
What is the link between potential difference, brightness/temperature and resistance?
As potential difference increases, so does brightness, temperature and resistance
61
Why does resistance increases as temperature/brightness increases?
Heat indicates more friction as positive ions vibrate more/with larger amplitude as more electrons try to pass through resulting in more collisions. This increases heat as there is more friction and more resistance as more particles move faster through the filament.
62
Is a filament bulb an ohmic conductor?
No because as voltage increases the potential difference increases by indirectly proportionally
Gradient = 1/R
63
What is an LDR?
Light dependent resistor
64
What does a LDR do?
Responds to changes in light intensity. It decreases when it’s bright (high light intensity)
65
Where are LDRs used?
In street lamps, light sensors
66
Describe light intensity / resistance graph:
- As Light intensity increases, resistance …
resistance decreases
Non linear relationship
Resistance decreases faster when light is low
At high light intenisty, resistance decreases gradually
67
What is an LED?
Light emitting diode
68
What does a diode do?
Only lets current flow in on direction, acting as a switch
69
What does an oscilloscope tell us?
About the voltage that is across a battery or power supply
70
What is DC?
Direct current
71
What is AC?
Alternating current
72
What does AC do?
Electrons oscillate/charge oscillates
+ —> —
— <— +
Changing direction
73
What does DC do?
+ —> - terminal
1 direction=constant value
74
What is Mains voltage in UK?
230V
75
What is the frequency of mains in UK?
50 Hz
76
What are the 9 parts of a plug?
1. Earth wire
2. Earth terminal
3. Live terminal
4. Fuse
5. Live wire
6. Cable
7. Cable grip
8. Neutral terminal
9. Neutral wire
77
What are the 3 types of wires in plugs?
1. Neutral wire
2. Live wire
3. Earth wire
78
Function of Earth wire:
Prevents fires and electrocution for safety purposes
79
Function of neutral wire:
Return wire, 0 volts
80
Function of live wire:
Alternating Pd
81
Colour of live wire:
Brown
82
Colour of Earth wire:
Yellow/green
83
Colour of neutral wire:
Blue
84
What does the cable do?
It’s an insulator
85
Dangers of live wires
If we have a metal casing it is a conductor
The case then becomes live
If a person touches the case they could become electrocuted (current flows through them)
86
What happens in terms of current when a person is electrocuted?
Current flows through them
87
How does the Earth wire protect the user?
Connects to metal casing. This route has more resistance than Earth which has little resistance causing the majority of the current to flow that way, person is safe
88
How does a fuse help to protect the user?
Large current causes it to heat up very quickly risking a fire. A fuse is a thin wire designed to melt (blow) when the current flowing through it hits the rated value.
This isolates the person from the live wires current as the fuse is connected to live wire - circuit is effectively broken
89
What is a fuse?
A fuse is a thin wire designed to melt (blow) when the current flowing through it hits the rated value.
90
How does double insulation protect the user?
Live wire can’t come into contact with any metal casing so person is safe
91
What does RCD stand for?
Residual current device
92
What does an RCD do?
Disconnects a circuit whenever it detects that the electrical current going into the device is not balanced with current coming out
93
What is the imbalance that the RCD usually disconnects as a result of it?
Current leakage through body of person who has touched live connection. Residual current flows through them
94
Where are RCDs used?
High power drills
Lawnmowers
95
Compare RCDs and Fuses:
RCD: disconnects circuit, easy to reset, stops under 20ms (quick), detects imbalance
Both: breaks circuit to protect from electrocution
FUSE: Melts thin wire when current flows above rated value, fiddly to replace, ‘slow’ in retail to RCD
96
What is an electric field?
An electric field is a region around a charged object where another charge experiences a non-contact electrostatic force (attraction or repulsion).
97
How to identify charge in an electric field?
these fields are shown with lines pointing away from positive charges and towards negative ones, with the lines closer together indicating a stronger field, strongest near the object itself.
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