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Physics Daisy > Electricity > Flashcards

Electricity Flashcards

1
Q

Blue wire in a plug

A

Neutral wire - 0 volts

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2
Q

Green wire in a plug

A

Earth - 0 volts

Contains an earth wire to provide an alternative path for the current if appliances develop a fault

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3
Q

Brown wire in a plug

A

Live - 230 volts

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4
Q

What happens if the live wire becomes lose?

A

It touches the metal case, so a very large current will flow to earth and blow the fuse, breaking the circuit

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5
Q

What is a fuse?

A

A built in weak point in a circuit - contains a thin wire with a higher resistance than a normal wire

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6
Q

What happens if a large current flows through the wire?

A

It becomes too hot so the wire melts and the circuit breaks

Makes a magnetic field produced by the electromagnet, strong enough to open the switch

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7
Q

Circuit breakers

A

Does the same job as fuses but they are electromagnetic switches which are easy to reset
Designed to break the circuit if the current gets too high

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8
Q

Energy transferred equation

A

Energy = current x potential difference x time

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9
Q

The larger the current …

A

The larger the current through a current the more the energy is transferred to it

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10
Q

In energy transfers, the higher the current…

A

The more energy transferred to the thermal energy stores of the components
This heating increases the resistance of the components

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11
Q

Electrical power

A

Power = energy transferred / time

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12
Q

Power

A

The energy that is transferred per second

Measured in watts

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13
Q

What does the power transferred by an appliance depend on?

A

Potential difference going across it

Current flowing through it

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14
Q

What does the potential difference tell you?

A

How much energy each unit of charge transfers

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15
Q

What does the current tell you?

A

How much charge passes per unit time

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16
Q

Power supplied equation

A

Power = current x voltage

Can use this equation to work out the fuse that should be used in an appliance

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17
Q

Power loss equation

A

P =current 2 x resistance

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18
Q

Alternating current

A

The charges are constantly changing direction

They are produced by alternating voltages

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19
Q

Direct current

A

The charges always move in the same direction
Created by a direct voltage
Supplied by cells and batteries

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20
Q

What is the uk mains supply?

A

Alternating current
50Hz
230 volts

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21
Q

What happens electrically if you touch a live wire?

A

A large potential difference is produced across your body and a current flows through you- this causes a large electric shock

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22
Q

Why are any connection between live and neutral can be dangerous?

A

If the link created a low resistance path to earth, a huge current will flow - could result in a fire

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23
Q

Why do surges in a current occur?

A

Changes in a circuit or because of a fault in an electrical appliance - can lead to wires in the appliance melting

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24
Q

Earth wire and fuses - how do they work?

A

Live wire touches metal case- the case in earthed do too great a current flows in through the live wire down the earth wire
Fuse melts- which are connected to the live wire, so that breaking the fuse breaks the circuit and cuts off the live supply

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25
Blowing a fuse in a toaster
A fault allows the wire to touch the metal A large current flows out through the earth wire to the earth This melts the fuse which isolates the appliance and makes it safe
26
LDR
Light dependent resistor In light the resistance falls In dark the resistance is high Automatic night lights
27
Thermistor
A temperature dependent resistor In heat , resistance drops In cold, resistance goes up Temp detectors
28
Current
The flow of electric charge around the circuit
29
When will a current flow?
If there is a potential difference across the component and if the circuit is complete - closed
30
Potential difference
The driving force that pushes the charge round | The energy transferred per unit charge
31
Resistance
Anything that slows the flow down
32
The higher the potential difference across a given opponent - the
Higher the current will be
33
The greater the resistance ...
The smaller the current that flows
34
Equation for total charge
``` Charge = current x time Q= I x T ```
35
Energy transfers from charge and potential difference equation
Energy transferred = charge x potential difference | E = Q x V
36
The potential difference across an electrical component is ...
The amount of energy transferred by the electrical component per unit charge
37
Potential difference , current and resistance equation
Potential difference = current x resistance | V=IxR
38
When an electrical charge flows through a component,
It has to do work against resistance. This causes an electrical transfer of energy - some of this energy is transferred usefully but some is dissipated to the thermal energy stores of the component
39
When current flows through a resistor, the resistor heats up Why is this?
The electrodes collide with the ions in the lattice that make up the resistor as they flow through it This gives the ions energy which coasters them to vibrate and heat up
40
The more the ions vibrate...
The harder it is for electrons to get through the resistor because there are more collisions. - this means that for a given potential difference the current decreases as the resistor heats up
41
What happens if the resistor gets too hot?
No current will be able to flow, there is one exception - the resistance of a thermistor decreases with an increase in temp
42
Series circuit
The different components are connected in a line, end to end
43
What happens if you remove one component from a series circuit?
The circuit is broken and they all stop working
44
Bigger supply - series circuit
There is a bigger supply of pd when more cells are in series
45
Current -series
The current us the same everywhere
46
Total potential difference - series
The total pd of the supply is shared between two components | The pd for each component depends on its resistance
47
Total resistance - series
The total resistance of the circuit increases as you add resistors
48
Parallel circuit
Each component is separately connected to the positive and negative supply
49
What happens if you remove a component from the parallel circuit?
It will hardly affect the others
50
Parallel circuit - pd
The potential difference is the same across all components
51
Current in a parallel circuit
Shared between branches - the total current flowing around the circuit is equal to the total of all the currents through the separate components
52
Total resistance of a parallel circuit
It decreases if you add a second resistor in parallel
53
What happens to the total resistance in a series circuit if you add a resistor?
The total resistance of two components is the sum of their resistances - this is because by adding a resistor in series , the two resistors have to share the total pd
54
The potential difference across each resistor ...
Is lower, so the current through each resistor is also lower
55
In a series circuit, the current is
The same everywhere so the total current in the circuit is reduced when a resistor is added - this means the total resistance of the circuit increases
56
The bigger a components resistance is ...
The bigger it’s share of the total potential difference
57
What happens if you have two resistors in a parallel circuit?
The total resistance is less than the resistance of the smallest of the two resistors
58
What happens to the resistance if there are two resistors in a parallel circuit? Explain
In parallel, both resistors have the same pd across them. - this means the pushing force making the current flow is the same as the source pd for each resistor By adding another loop the current can flow in more than 1 direction This increases the total flow around the circuit
59
Using V=IxR an increase in current...
Means a decrease in the total resistance of the circuit
60
Energy in circuits equation
E = I x V x T | Energy transferred = current x pd x time
61
When is energy transferred?
When an electrical charge goes through a charge in potential difference
62
The larger the current or pd ...
The more energy is transferred to it
63
voltmeter in circuits
is connected in parallel with a component to measure the potential difference in across it, volts
64
Ammeter in circuits
is connected in series with a component to measure the current in the component, amps
65
Where is the current conserved?
at a junction in the circuit
66
what does the standard circuit test do?
investigates the relationship between current, potential difference and resistance for things like a filament light bulb, fixed resistor
67
why do you use a variable resistor in the standard circuit test?
it is used to change the current through the circuit. As I=V/R, increasing the total resistance by increasing the variable resistors resistance it decreases the current
68
What does the circuit look like in the standard circuit test?
make circuit- component, ammeter, and resistor is in series. voltmeter must be put into parallel
69
Method in standard circuit test
change resistance of the variable resistor - measure the current through the pd across the component take reading from ammeter and voltmeter - calculate means
70
what does the graph look like for the standard circuit test?
current against the pd | work out the resistance for each measurement
71
what are the safety precautions in the standard circuit test?
make sure it doesn't get to hot - if it does it will mess up your results
72
LDR - what is it? Resistance What are they used for?
A resistor that depends on the intensity of light bright light - resistance falls dark - resistance at its highest automatic night lights and burglar detectors
73
thermistor - what is it? resistance what are they used for?
a temperature dependent resistor hot - resistance drops cold - resistance goes up temp detectors, car engine temp sensor
74
what do iv graphs show?
how current varies as you change the pd
75
what does the iv graph look like for resistors and wires?
``` straight diagonal line going from left to right goes through (0,0) - linear graph ```
76
explain the iv graph for resistor and wires
current is directionally proportional to the pd
77
What does the iv graph look like for a filament light bulb?
a diagonal s | from left to right
78
explain the iv graph for a filament light bulb
the increasing current increases the temp of the bulb which increases the resistance of the bulb
79
what does an iv graph look like for a diode?
straight line from top left to curve in top right
80
explain the iv graph for the diode
current will only flow through a diode in one direction | the diode has a very high resistance in the other direction
81
method of investigating circuits with adding resistors
set out circuit vary the output pd from the power supply - record the readings replace the resistor with a filament lamp then connect a second fl vary the output pd write down current and pd
82
what are the results for adding a filament or resistor into a series circuit?
as the pd increase, the current through the resistor increases you should a similar but not linear relationship between pd and current for filament light bulb
83
what are the results for adding a filament or resistor into a parallel circuit?
as the pd increases the current increases through each bulb - non linear relationship total current is the sum of the current though the branches but this is bigger than the current through the series circuit overall resistance is low
84
when there is an electric current in a resistor there is...
an energy transfer which heats the resistor
85
energy transfer in a kettle
electrical energy from the mains ac supply to the thermal store of the heating element in the kettle
86
energy transfer in a electrical hand held fan
electrical energy transfer from the battery to the kinetic energy store in the fans motor
87
what happens if the current is higher in an energy transfer?
the higher the current, the more energy transferred to the thermal energy store of the components and then surroundings
88
what does the increase of heating of an object do to the resistance?
increases the resistance of the components
89
what happens during the heating of a wire?
As electrons flow through wires, they collide with the ions in the wire which causes the ions to vibrate more. This increased vibration of the ions increases the temperature of the wire.
90
what happens if the circuit gets too hot?
can cause components in the circuit to melt which means the circuit will stop and not work properly
91
what do fuses do?
they protect circuits by melting and breaking the circuit if the current gets too high
92
advantages of the heating of an electric current - toaster
toasters contain a coil of wire with a high resistance | when a current passes through the coil, its temp increases so much it glows and gives off infrared radiation
93
disadvantages of heating an electric current
heating up a component generally reduces its efficiency | if the temp gets too high then the circuit melts and breaks

Physics Daisy (11 decks)

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