P2- Electricity Flashcards
(104 cards)
1
Q
Define current
A
The flow of charged particles
2
Q
The _ the resistance across a component, the _ the current that flows
A
Greater
Smaller
3
Q
What is the equation for total charge
A
Charge flow = Current X time
4
Q
What is the equation for potential difference
A
Potential difference=Current X resistance
5
Q
What do ohmic conductors have
A
Constant resistance
6
Q
What does LDR stand for
A
Light dependent resistor
7
Q
What does the resistance of a thermistor depend on
A
Temperature
8
Q
What happens to the resistance of a thermistor in different temperatures
A
Hot goes up cold goes down
9
Q
How can you use LDRs and thermistors
A
in sensing circuits
10
Q
How can sensing circuits be used
A
To turn on or increase the components depending on the conditions they are in
11
Q
How are components arranged in a series circuit
A
Around in a line
12
Q
What is the equation for total potential difference in a series circuit
A
Vtotal=V1+V2+…
13
Q
What is the equation for current in a series circuit
A
I1=I2…..
14
Q
What is the equation for total resistance in a series circuit
A
Rtotal=R1+R2
15
Q
What is the equation for potential difference in a parallel circuit
A
V1=V2
16
Q
What is the equation for current in a parallel circuit
A
Itotal=I1+I2+…
17
Q
What does adding a resistor do to the total resistance in a parallel circuit
A
Reduces the total resistance
18
Q
What type of supply is the mains supply
A
AC
19
Q
What type of battery supply is used
A
DC
20
Q
What does AC current do
A
Constantly change direction
21
Q
What does DC current do
A
Constantly flow in the same direction
22
Q
How many wires do most cables have
A
3
23
Q
What are the 3 different wires in most cables
A
- Live wire
- Neutral wire
- Earth wire
24
Q
What is the live wire
A
The wire provides the alternating potential difference from the main supply
25
What is the neutral wire
The neutral wire completes the circuit- when the appliance is operating normally, current flows through the live and neutral wires
26
What is the Earth wire
It's protecting the wiring, and for safety - it stops the appliance casing from becoming live. It doesn't usually carry a current- only when there is a fault
27
Can the live wire give you an electric shock
Yes
28
What is the equation for energy transferred
Energy transferred= Power(w) X Time(s)
29
What is the equation for energy transferred
E= Charge flow X potential difference
30
What is the equation for power including potential difference and current
P =VI
31
What is the equation for power including resistance and current ( this may be wrong)
P=I^2R
32
What is potential difference changed by
A Transformer
33
What does a build up of static electricity cause
Friction
34
When too much static electricity causes a spark what is there a lot of
Potential difference
35
Similar charges _ ,opposite charges _
Repel
| Attract
36
What do electric charges create
Electric field
37
Where is an electric field created around
Electrically charged object
38
How can you show an electric field
Field lines
39
Charged objects in an electric field fell a _
Force
40
When are sparks caused
When there is a high enough potential difference between a charged object and the Earth
41
Define charge
Value of electricity flowing in a circut
42
Define current
Flow of electrons
43
Define potential difference
Pushes current around
44
Define define resistance
Anything that slows down the current
45
Give two example of when a thermistor may be used
1. In a thermistat to turn a heater on below a certain tempreture
2. In a freezer to turn on a cooler when the temperature becomes too high
46
State what happens to the resistance of an LDR as the light intensity increases
The LDR's resistance increases
47
Give an application for an LDR
○ Street lights
| ○ When light levals become too low, the light gains sufficient current to turn on
48
State the equation linking charge, current
and time. Give the units for the quantities
involved.
Q = I t
Charge (Coulombs), Current (Amperes),
Time (Seconds)
49
What can be said about the value of
current at any point in a single closed
loop?
Current is the same at all points in a
| closed loop
50
What two factors does the current in a
| circuit depend on?
1. Potential Difference (V)
| 2. Resistance (R)
51
What equation should be used to
calculate potential difference if current
and resistance are known? State the
units for all 3 quantities.
```
V = I R
Potential Difference (V), Current (A),
Resistance (Ω)
```
52
What is an ‘Ohmic Conductor’? State the
| condition required.
```
● A conductor for which current and potential
difference are directly proportional
● Resistance remains constant as current
changes
● Temperature must be constant
```
53
List four components for which
resistance is not constant as current
changes
1. Lamps
2. Diodes
3. Thermistors
4. Light Dependant Resistors (LDRs)
54
What happens to the resistance of a
filament lamp as the temperature
increases? Why?
● Resistance increases
● Ions in metal have more energy, so vibrate
more, causing more collisions with
electrons as they flow through the metal,
creating greater resistance to current flow
55
What is different about current flow
| through a diode?
● The current only flows in one direction
● Resistance is very high in the other
direction, preventing current flow
56
State what happens to the resistance of
| a thermistor as temperature increases.
The thermistor’s resistance decreases.
57
Give two examples of when a thermistor
| may be used.
1. In a thermostat to turn a heater on
below a certain temperature
2. In a freezer to turn on a cooler when
the temperature becomes too high
58
State what happens to the resistance of
| a LDR as light intensity decreases.
The LDR’s resistance increases.
59
Give an application for a LDR.
● Street lights often use LDRs
● When light levels become too low, the
light gains sufficient current to turn on
60
What are the two ways that a component
| can be connected in a circuit?
1. Series (same loop)
| 2. Parallel (adjacent loop)
61
How does the potential difference across
two components vary when connected in
series and parallel?
● Series: Total P.D is shared between
each component
● Parallel: P.D across each component
is the same
62
If two resistors are connected in parallel,
what can be said about their combined
total resistance?
Their total resistance is less than the
smallest of the two individual
resistances.
63
If two resistors are connected in series,
what can be said about their total
resistance?
Their total combined resistance is equal
to the sum of the two individual
resistances
64
Describe the current in a series circuit.
In a series circuit, the current is the same
at all positions since the charge only has
one path to flow through.
65
Describe the current in a parallel circuit.
In a parallel circuit, the current is shared
between the different branches. When
the charge reaches a junction it splits.
66
How should you connect an ammeter in a circuit to
| measure current?
Ammeters should be connected in series
with the component that they are
measuring current through.
67
How should you connect a voltmeter in a
| circuit to measure potential difference?
Voltmeters should be connected in
parallel to the component that they are
measuring the potential difference of
68
Why is it advantageous to connect lamps in parallel?
If one lamp blows, the rest will be
unaffected and can still receive current
(i.e. the circuit is still complete).
69
Is mains electricity an a.c supply or a d.c
supply? What do each of these stand
for?
Mains electricity is an a.c supply
a. c. : Alternating Current
d. c. : Direct Current
70
Define alternating current and direct current.
```
● Alternating current: Current that
continuously changes direction at a
specific frequency
● Direct current: One directional current
flow
```
71
What is the frequency and voltage of the UK mains
| electricity supply?
● Frequency: 50 Hz
| ● Voltage: 230V
72
How many wires are usually in the cables connecting
electrical appliances to the mains? Name these
wires.
1. Live wire
2. Neutral wire
3. Earth wire
73
State the insulation colour used on the Earth wire.
Green and Yellow Stripes
74
State the insulation colour used on the live wire
Brown
75
State the insulation colour used on the Earth wire.
Blue
76
Explain when the Earth wire does and doesn’t carry
| a current.
● Under normal circumstances, no current
flows through the Earth wire
● If a fault occurs in the appliance (such as a
surge or the casing becoming live), current
will flow to the ground
77
What potential is the neutral wire at?
0 Volts
78
State the potential difference between the live and
| earth wires.
230 Volts
79
What is the purpose of the neutral wire?
To complete the circuit by connecting the
| appliance back to the mains supply.
80
For metal appliances, where is the Earth wire
| connected to? Why?
● Earth wire is connected to the metal casing
of the appliance
● If live wire becomes loose and touches the
casing, the current will flow through the
Earth wire, preventing electrocution
81
State two equations for the power of a circuit. Give
| appropriate units.
P = I V P = I² R
Power (Watts), Current (Amperes)
Potential Difference (Volts), Resistance
(Ohms)
82
State an equation linking energy transferred, power
| and time. Give appropriate units.
E = P t
Energy (Joules), Power (Watts), Time
(Seconds)
83
State an equation linking energy transferred, power
| and time. Give appropriate units.
```
E= Q V
Energy (Joules), Charge (Coulombs),
Potential Difference (Volts)
```
84
What two main factors does the amount of energy
| transferred by an appliance depend on?
1. How long the appliance is being used
for
2. The power of the appliance
85
Describe the energy transfers in a battery powered
| torch.
```
● Battery converts chemical energy into
electrical energy
● Bulb converts electrical energy into light
as well as waste energy in the form of
heating
```
86
Describe the energy transfers in a battery powered
| motor.
```
● Battery converts chemical energy into
electrical energy
● Motor converts electrical energy into
kinetic energy as well as waste energy
in the form of heating due to friction
```
87
What three things determine the power of a circuit
| device?
```
1. The potential difference across the
circuit
2. The current through the circuit
3. The amount of energy transferred in a
given time
```
88
What is the purpose of the National Grid?
To link power stations to consumers so
that they have access to a source of
electricity.
89
What are the two types of transformers used in the
| National Grid?
1. Step-Up Transformers
| 2. Step-Down Transformers
90
Where are step-up transformers found in the
| National Grid? What do they do?
● Step-Up Transformers are used when
connecting power stations to
transmission cables
● They increase the potential difference
91
Where are step-down transformers found in the
| National Grid? What do they do?
● Step-Down Transformers are used in
connecting transmission cables to
domestic buildings (like houses)
● They decrease the potential difference
92
Why do transmission lines transfer electricity at high
| potentials?
● A high potential, results in a low current
● The lower the current, the less energy
that is wasted as heat
● Therefore it is more efficient
93
Why does the potential need to be decreased
| between transmission lines and houses?
● Lower potentials are safer for domestic
use and reduces the likelihood of
severe electrocution
● Appliances are designed for 230V
94
What can happen when insulating
| materials are rubbed together?
They can become (statically) electrically
| charged.
95
Why can insulators become electrically charged
| when rubbed together?
● Electrons are rubbed from one material onto the
other
● The material gaining electrons becomes
negatively charged
● The material losing electrons becomes equally
positively charged
96
What happens when two electrically charged objects
| are brought close together?
They exert a force on each other
97
What happens when two identically charged objects
| are brought close together?
They exert a repulsive force on each
| other and repel.
98
What happens when two oppositely charged objects
| are brought close together?
They exert an attractive force on each
| other and attract.
99
Give an example of a non-contact force.
The repulsive or attractive force acting
| between two electrically charged objects.
100
What is an electric field?
A region in which a charged object will
| experience a non-contact electrical force.
101
Where can electric fields be found?
Surrounding any charged object.
102
Describe the electric field around a
| charged particle.
● Strongest closest to the object
● Decreases in strength as you move
away from the object
103
What happens to the force between two charged
| objects when they are moved closer together?
The force between them becomes
| stronger as the separation reduces.
104
In situations where sparks are unwanted,
what precaution must be taken to
prevent the build up of static charge?
Any surfaces that are rubbing against
each other should be earthed to allow
the charge to flow off the materials.
