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Physics paper 1 > Electricity > Flashcards

Electricity Flashcards

1
Q

Thermistor

A

The resistance of the thermistor depends on its temperature. At low temps the thermistor has a high resistance.

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2
Q

LDR (light dependent resistor)

A

At low light levels, LDR has high res

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3
Q

Where can u use LDR’s

A

Sensor in cameras or automatic lights that come on when it gets dark

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4
Q

Semi conductor diode

A

Allows current to flow in one direction only Current only flow in the other direction. Diodes are used to convert an alternating current into a direct current

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5
Q

Charge formula + units

A

QIT =
q= I * T
Charge = current * time
Charge = coulombs
Current = amps
Time = seconds

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6
Q

What two other factors other than amount of amps decide on the current through a component

A

The resistance of the component and the potential difference across the component

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7
Q

How do u measure potential difference across a component

A

A voltmeter must be placed in parrallel with that component.

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8
Q

Potential difference =
to calculate work power

A

Potential difference = energy/charge
Energy = joules
V=E/Q

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9
Q

Potential difference =

A

potential difference = current * resistance

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10
Q

A thinner wire increases what

A

resistance

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11
Q

A longer wire increase

A

resistance

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12
Q

Practical Changing the length of the wire affects its resistance

FIRST HALF steps 1-4

A
  1. Connect the circuit as shown in the diagram above.
  2. Connect the crocodile clips to the resistance wire, 100 cm apart.
  3. Record the reading on the ammeter and on the voltmeter.
    4.Move one of the crocodile clips closer until they are 90 cm part
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13
Q

Practical Changing the length of the wire affects its resistance

SECOND HALF steps 5-8

A
  1. Record the new readings on the ammeter and the voltmeter.
  2. Repeat the previous steps reducing the length of the wire by 10cm each time down to a minimum length of 10 cm
    7.Use the results to calculate the resistance of each length of the wire by using r=v/i, where R is the resistance V is the voltage and I is the current
    8.Plot a graph of the resistance against the length for the resistance wire.
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14
Q

Practical Changing the length of the wire affects its resistance

HAZARDS
consequences
control measures

A

Heating of the resistance wire
burns the skin
Do NOT touch

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15
Q

Neutral wire color and purpose (2)

A

Blue that completes the circuit in a mains power supply

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16
Q

Ohmic conductor (2)

A

A conductor whose current flow is directly proportional to the potential difference across it. When held at a constant temperature.

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17
Q

Static charge

A

The charge caused by an imbalance of positive and negative charges in, or on an objects surface. It is often caused by electrons being rubbed from one surface to another.

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18
Q

Fixed resistor and potential difference relationship

A

They are directly proportional to eachother.

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19
Q

Relationship between filament bulb and potential difference sketch graph in paint.

A

https://bam.files.bbci.co.uk/bam/live/content/zcdnk2p/large

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20
Q

filament bulb relationship between energy input current to flow and the resistance potential difference and temprature

(5)

A

The more energy that is put into the bulb, the harder it is for the current to flow - the resistance of the bulb increases. As the potential difference increases, so does the temperature of the thin wire inside the bulb, the filament. The higher the temperature increases the vibrations of the ions which makes it harder for ions in the filament, which makes it harder for the electrons to get past.

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21
Q

Potential difference and current graph with semi conductor

Sketch in paint

A

https://bam.files.bbci.co.uk/bam/live/content/zwmb7p3/large

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22
Q

Circuit rules SERIES (2)

A

An electron will pass through every component on its way round the circuit. If one of the bulbs is broken then current will not be able to flow round the circuit. If one bulb goes out, they will all go out

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23
Q

How calculate total resistance in series circuit

A

Rtotal = R1+R2 ectr

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24
Q

Series circuits (3)

A

Current is the same through each component

Total potential difference of the power supply is shared between the components

The total resistance of the circuit is the sum of individual resistors

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25
Circuit rules parallel
An electron will not pass through every component on its way round the circuit. If one of the bulbs is broken then current will still be able to flow round the circuit through the other loop. If one bulb goes out, the other will stay on
26
Current in parallel
Since there are different loops, the current will split as it leaves the cell and pass through one or other of the loops. An ammeter placed in different parts of the circuit will show how the current splits
27
Calculate current in parallel
i1= i2 + i4 = i3
28
How is potential difference shared around in parallel circuits
Equally
29
Resistors in parallel circuits
The supply current is divided between them. The overall resistance is reduced as the may
30
Parallel circuits (3)
The total current supplied is split between the components on different loops Potential difference is the same across each loop The total resistance of the circuit is reduced as the current can follow multiple paths
31
Heating up wires explained in terms of energy
As electrons flow through wires they collide with the ions in the wire which causes the ions to vibrate more. This increased the vibration of the ions increases the temperature of the wire. Energy has been transferred from the chemical energy store of the battery into the internal energy store of the wire
32
Power =
power = current * potential difference
33
Power = with resistance
Power = current^2 *r resistance
34
How to be more efficient with wires
Having a higher current will have a much higher heating effect on the transmission wires have than a low current. For this reason, transmitting energy at a high voltage with a low current will keep the wires cooler and waste less energy.
35
Uses of DC
car batteries, dry cells and solar cells
36
On a graph quickly sketch in snipping tool what a DC voltage-time graph would look like
https://bam.files.bbci.co.uk/bam/live/content/zv2v9j6/small
37
On a graph quickly sketch in snipping tool what a AC voltage-time graph would look like
https://bam.files.bbci.co.uk/bam/live/content/z3m3kqt/small
38
What is the UKs, main electricity supply is generated at frequency and delivered to houses at what volts
50 Hz 230 V
39
In a plug what is the brown wire, the blue wire and the green/yellow wire
Brown wire = live wire blue wire = neutral wire green/yellow wire = earth wire
40
earth wire
Copper wire coated in striped plastic that provides a path for the current to flow from the case of the device to the ground if there is a fault
41
Neutral wire
copper wire coated with blue plastic that also connects to the cable in the wall and completes the circuit.
42
Live wire
The copper wire coated with brown plastic along the current enters the device
43
Cable grip
This holds the cable tightly in place so that the wires do not become loose.
44
Outer insulation
All three wires in the cable are bundled together and there is extra plastic wrapped round all for safety.
45
What if the earth wire fails to complete its function
The live wire would become loose, there is a danger that it will touch the case. The next person who uses the appliance could get electrocuted
46
Why is the earth wire made of copper
To provide a low resistance path to the ground.
47
Fuses purpose and how it could melt (4)
A fuse prides a built in fail safe to the electrical circuit for a device. This fuse contains a thin wire that will melt if the current gets too high. If there is a fault that causes the casing of the device to become live, a large current will flow through the low-resistance earth wire. This will cause the fuse to melt
48
Once the fuse has melted what happens to the circuit
Current no longer flows through the device. Meaning the device is no longer alive and there is no more risk of electrocution
49
In terms of energy how do electrical appliances transfer energy from one store to another give an e.g
Chemical energy in the fuel in power stations. This is transferred into k.e in a fan or heat energy in a cooker
50
Energy =
energy = power * time
51
How does electricity go from the power station to your house factories and shops and such places
Power station --> step up transformers --> high voltage transmission lines --> step down transformers --> homes, factories and shops
52
National grid
Distributed electricity across the country. The national grid connects power stations to homes, workplaces and public buildings all around the country.
53
National grid produces energy how
The electricity may be produced by a conventional power station turning a generator or by another method.
54
Transformers work how
A transformer is formed when two coils of wire around a magnetic core. The number of coils determines whether the transformers will step up or step down the voltage.
55
In the national grid a step up transformer does what to voltage and the current and increases voltage or current by how much
Increases voltage and reduces current 25000 V ---> 400,000 V
56
Why do the national grid want there to be less current when transferring it across pylons
Less current means less energy is lost through the heating of the wire.
57
How does the national grid keep people safe from high voltage wires
Pylons are used to support transmission lines above the ground.
58
Before reaching the end user a step down transformer reduces the transmission voltage to a safer voltage of
230 V
59
What two factors decide how much electrical power dissipates on transmission lines and how
An electrical current flows through thick cables held up by pylons they will get hotter and dissipate energy to the surroundings. The electrical power dissipated depends on the current and resistance
60
How do the national grid minimise the amount of power lost through transmission cables
The cables are thick so that their resistance is low High voltages are used to reduce the current through the transmission lines
61
Static electricity
Electric charge that accumulates on an insulated object,
62
When insulating materials rub against each other what happens
each other they may become electrically charged.
63
Practical factors affecting resistance on a circuit focus on length of wire + results what the graph would look like (8)
We will be using the ammeter to measure the current and of the circuit and the voltmeter to measure the potential difference across the wire Then use these values to calculate the resistance R=v/i Attach a wire to a meter ruler using tape. Connect wire into rest of the circuit by using two crocodile clips. Place the clips on the wire. Measure the distance between the crocodile clips and that is the amount of wire that you are using. You can alter where the crocodile clips are move one further away from the other to give the circuit more wire and see if the resistance changes You should find out that the result is that the resistance of the wire is directly proportional to the length
64
Zero error
A zero error is a reading on a measuring instrument when the value should be zero.
65
In the case of measuring resistance and you had a 0 error what would you do
Subtract the zero error from all of our readings
66
Reasons why there could be a zero error with the Practical factors affecting resistance on a circuit focus on length of wire
You cannot get the crocodile clip at exactly 0 There is also some resistance caused by the contact between the crocodile clip and the wire,
67
Practical factors affecting resistance on a circuit focus on length of wire Heating effects how to reduce and the problem
If the temperature of the wire increases then the resistance will also increase Use a low potential difference. This will keep the current low, reducing any heating in the wire. Only turn on the current when taking a reading. Turn off the current between readings
68
If a cloth was to be rubbed against plastic rod what would happen in terms of positive charge
The cloth would now have a negative charge due to having more electrons and the plastic would have a positive charge due to less electrons
69
How can static electricity be dangerous in fueling airplanes
Electrostatic charge can build up as fuel flows through the refueling pipe. This could cause a spark and trigger an explosion
70
How can static electricity be dangerous in fueling airplanes how can we prevent
To prevent that, both are refueling truck and aeroplane are earthed. This prevents any charges from building up and leading to a spark
71
Objects of opposite charges attract/repel
attract
72
Objects of same charges attract/repel
repel
73
When touching a grandeur generator why might someones hair stick up
Each hair is positively charged so they repel away from each other
74
Scientists show an electric field how
through field lines that are perpendicular to the surface of the object

Physics paper 1 (4 decks)

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