SP10 Flashcards
(69 cards)
1
Q
Define current
A
- Rate of flow of charge in circuits
- Measure of flow of electrons in metals
2
Q
Define potential difference
A
- The force that drives electrons around a circuit
- The energy transferred per unit charge (1J/C)
3
Q
Define resistance
A
Anything that stops/opposes the flow of electrons thus slows it down
4
Q
Which way do electrons flow in a circuit
A
From the positive terminal to the negative terminal
5
Q
Define charge
A
The amount of electrons that flow around a circuit in a specific period of time
6
Q
What is the relationship between current and resistance
A
Inversely proportional
7
Q
What is required for current to flow
A
- potential difference
- closed circuit
8
Q
Equation for charge
A
Q = I * t
9
Q
Equation for Voltage
A
V = I * R
10
Q
Features of a series circuit
A
- If one component breaks, whole circuit disconnects
- Potential difference is shared across all components
- Current is the same anywhere in the circuit
- Resistance is shared across all components
- Components with higher resistance have a greater share of the voltage
11
Q
How is an ammeter placed
A
In series
12
Q
How is a voltmeter placed
A
In parallel
13
Q
Features of a parallel circuit
A
- If one component breaks, the rest will remain unaffected
- Voltage is the same at all components
- Current is shared across all components
- Loops with greater resistance have a lower share of current
- More components in parallel decreases total resistance
14
Q
How does a filament lamp work
A
- Current flows through filament
- Wire heats up and emits light
15
Q
Why does the slope decline in a filament lamp graph
A
- As wire emits light it gives off heat
- This increases resistance thus decreasing current
16
Q
Describe how a diode works
A
Current only flows in one direction (when p.d. is positive) as there is extremely high resistance when voltage is negative
17
Q
Describe how to investigate a component
A
- Use a power supply that provides different voltages
- Turn it down to its lowest voltage
- Take a pair of readings to observe how current through a component and voltage across the component vary
- Repeat, increasing voltage each time
- Plot a current-voltage graph
- Calculate resistance to see how resistance varies
7.. If circuit gets too hot - disconnect power supply
18
Q
Why must you disconnect power supply if circuit gets too hot when investigating components
A
- Increase heat = Increase resistance
- It will affect results and make them inaccurate
19
Q
Why do resistors heat up when current flows through them
A
- There is an electrical transfer of energy some of it is dissipated to the thermal energy stores of the resistor
20
Q
Why does less current flow through as the temperature of a resistor increases
A
- Electrons collide with the ions in the lattice (that makes up the resistor) and give them energy
- Ions vibrate faster making it harder for electrons to get through resistor (increase no. collisions)
21
Q
What is special about a thermistor
A
As temperature increases, resistance decreases
22
Q
What does LDR stand for
A
Light dependent resistor
23
Q
What is special about LDRs
A
As light level increases, resistance decreases
24
Q
What are LDRs used for
A
- Automatic night lights
- Outdoor lighting
- Burglar detectors
25
What are thermistors used for
- Car engine temp sensors
- Electronic thermostats
26
Describe how to investigate voltage
27
Equation for energy transfer
E = V * I * t (V * Q)
28
Why does the resistance decrease if there are more resistors in parallel
The current has more pathways to go through making it easier to flow through circuit
29
Why does the resistance increase if there are more resistors in series
More resistors increase the resistance as current has to pass through each one
30
How to investigate the variation in resistance in a **diode**
- Take measurements for a range of currents
- Remove the diode and swap its direction
- No current can flow through (high resistance)
31
How to investigate the variation in resistance in a **LDR**
- Conduct experiment in a dim room
- Keep p.d. constant
- Use a lamp to change light level
- As light increases, resistance decreases
32
How to investigate the variation in resistance in a **thermistor**
- Keep p.d. constant
- Increase temp of thermistor by placing a beaker of hot water next to it
- As temperature increases, resistance decreases
33
Explain the design and construction of series circuits for testing and measuring
- Different components are connected in a line, between positive and negative terminals
- Series is used because it is easier to change, measure and calculate voltage, current and resistance
34
How is current conserved
The amount of current flowing into a junction is equal the amount flowing out
35
Describe how to construct a circuit to test series and parallel circuits using resistors and filaments (Practical X)
1. Set out a circuit with a resistor I, ammeter and voltmeter
2. Change power supply output and record readings from ammeter and voltmeter
3. Add resistor II and repeat step 2
4. Place resistor II in parallel and repeat step 2
5. Replace resistors with filament lamps and repeat step 2-4
36
What results should you expect to see from a series circuit in Practical X
- As p.d. increases so should current through the (fixed) resistor
- They have a linear relationship
- As p.d. increases so should current through the filament lamp
- They have a non-linear relationship
37
What results should you expect to see from a parallel circuit in Practical X
- As p.d. increases, so does the current through each bulb/resistor
- They have a non linear relationship
- The p.d. across each bulb is the same as the p.d. through the power supply
38
Explain how to reduce unwanted energy transfers
- Use low resistance wires made from metals such as cooper
- Use thicker wires
- Use cooling metals
39
What are the advantages of the heating effect of a current
+ Fuses use this effect to protect circuits by melting when and breaking it
+ Useful for heating appliances e.g. toasters
40
What is the disadvantage of the heating effect of a current
- Reduces efficiency of appliances
41
Define power
The energy transferred per second
42
What does the power rating of appliance tell you
The maximum amount of energy transferred between stores per second
43
What is power dependent on
- Potential difference - how much energy is transferred per charge
- Current - how much charge passes per second
44
Equation for electrical power
P = I * V
45
Equation for electrical power when voltage is unknown
- V = I * R
- P = I * V
- **P = I * I * R**
46
What is the difference between alternating current and direct current
- Alternating current uses an alternating potential difference
- Direction of current is always changing
- Direct current uses a direct p.d.
- Direct currents charge is always flowing in the same direction
47
Name a use for alternating current
UK mains supply
48
Name a use for direct current
- Batteries
- Cells
49
How are oscilloscopes used
Display current-time graphs
50
What wires are in the three core cable
- Live
- Neutral
- Earth
50
What is the domestic supply in the UK
- A.C.
- 50 Hz
- 230V
51
What are the colours of the the core cable wires
- Live = brown
- Neutral = blue
- Earth = green and yellow
52
What is the function of the **live** wire
- Provides alternating voltage at 230V
- Electricity flows into the device through it
53
What is the function of the **neutral** wire
- Completes circuit
- Carries away current
- Electricity flows out of device through it
54
What is the function of the **earth** wire
- Stops casing from becoming live
- Provides an alternate pathway for current to flow through
- Does not carry current
55
Why can electricity flow between the three wires
There is a difference in voltage
56
Why can electricity flow through humans
- They have 0 potential difference
- There is a difference in voltage therefore a large current can flow through
- They provide a low resistance pathway to earth
57
What are the wires made of
- Insulating plastic
- Copper
58
What do fuses, circuits, earth wires and double insulation have in common
They are safety precautions in place to prevent the risks that come with dealing with electricity
59
How is energy transferred from a battery/ a.c. motor to the energy of a motor/ heating device
- Energy is transferred via electrical work
- Energy is transferred to devices kinetic/thermal store
60
Describe the function of **fuses**
- If a high current passes through, wire will melt as it is thin
- Break circuit as current cant flow
- Rating of fuse is a little bit higher than rating of appliance
61
Describe the function of **earthing**
- Earth wire provides an alternate pathway for current
62
Describe the function of **double insulation**
- Entire appliance is covered in insulating plastic = no exposed metal
- No need for earth wire = two core cables
63
Advantages of circuit breakers
- Faster than fuse melting
- Resettable
64
Advantages of fuses
- Cheaper
- Simpler to use
65
Disadvantage of circuit breakers
Expensive
66
Disadvantages of fuses
- Permanently broken after surge
- Needs to be replaced
67
Why should fuses and switches be connected in the live wire
To ensure that a high voltage does not reach the user or surroundings
68
What are the voltages of the wires in a three core cable
- Live - 230V
- Neutral - 0V
- Earth - 0V
