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Science > Electricity and Circuits > Flashcards

Electricity and Circuits Flashcards

1
Q

What does a fuse do?

A

Protects electrical circuits and appliances

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2
Q

How does a fuse work?

A
  • The fuse breaks the circuit if a fault develops
  • This protects the wiring and the appliance
  • The fuse contains a wire which melts easily
  • If the current is too great, the wire heats up and melts until it breaks the circuit
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3
Q

What is the function of the Earth wire?

A
  • many electrical appliances have metal cases

- the earth wire creates a safe route for the current to flow through if the live wire touches the casing

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4
Q

What are the three wires in a double insulated plug?

A

Live, neutral and Earth

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5
Q

What happens if the live wire touches the casing?

A

You get a severe electric shock and it can also cause the wire to heat up, causing a fire and can cut off the mains electricity supply

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6
Q

Why is the Earth terminal connected to the metal casing?

A

So the current goes through the Earth wire instead of the live wire and causes an electric shock. This breaks the fuse and disconnects the appliance

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7
Q

What do the electrons have to be in order for them to be used for electrical wiring?

A

They have to have one electron in their outer shell in, so that they are weakly attached to the nucleus. These electrons can be easily removed, so an electrical wire has a lot of ‘free electrons’

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8
Q

What does a battery do to the free electrons in an electrical wire for example?

A

The voltage pushes the free electrons around the circuit. These electrons are also negatively charged, so they move towards the negative terminal of the battery

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9
Q

What is the conventional direction of current flow?

A

It goes from the positive terminal to the negative of the battery cell, and is opposite to the direction of electron flow

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10
Q

What does a parallel circuit allow?

A

Different routes for the current to go down

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11
Q

What does it mean if a lamp breaks in a series and parallel circuit?

A

Series- whole circuit will shut down

Parallel- it will find a different route to go down instead

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12
Q

What happens to the total amount of current throughout a circuit and what is this called?

A

It stays the same and is called conservation

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13
Q

In a parellel circuit, does the total amount of current also stay the same?

A

yes- it is conserved and divided between its components in different branches

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14
Q

At only what point will current flow?

A
  • When there is a potential difference (voltage) to move the free electrons
  • Circuit must be closed
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15
Q

What is the relationship between potential difference and current?

A

Directly proportional

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16
Q

What happens to the potential difference when there is more than one component in a circuit branch?

A

The potential difference in that branch adds up to the total potential difference supplied by the battery or cell

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17
Q

What is electrical charge measured in?

A

Coulombs (C)

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18
Q

What do moving electrically charged particles make?

A

An electrical current

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19
Q

What is the relationship of a 1 coulomb with amps and seconds?

A

One coulomb is the charge passing a point in a circuit when there is a current of 1 amp for 1 second

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20
Q

What is the charge of one electron?

A

-1.6 x 10^-19 ( very small)

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21
Q

What does the size of the current at any point in a circuit tell you about charge?

A

That is how much charge is flowing at that point each second - Electric current is the rate of flow of charge

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22
Q

How do you calculate charge:

A

Current x time

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23
Q

Explain how energy from a cell is transferred to the components of the circuit

A
  • A cell contains a store for energy
  • Energy is transferred to the charge
  • The charge can now transfer energy to the components in the circuit - it has potential energy
  • Energy is transferred from the charge as it moves through the lamp
  • The lamp transfers the energy as heat and light into surroundings
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24
Q

What is the relationship between potential difference and charge?

A

The potential difference of a cell is the amount of potential energy the cell transfers to each coulomb of charge flowing through it

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25
Q

How do you work out energy transferred?

A

Energy transferred = charge moved x potential difference

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26
Q

Why do some wires and components need a larger potential difference to produce current?

A

Because they have a higher resistance

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27
Q

How do you work out potential difference?

A

V = current (amps) x resistance (ohms)

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28
Q

What happens when resistors are connected in series?

A

The total resistance of the circuit is increased because the pathway becomes harder for the current to flow through

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29
Q

What happens to the potential difference when resistors are connected to a series circuit?

A

The potential difference is shared between the resistors but it may not be shared equally. There will be greater potential difference across resistors with higher resistances

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30
Q

What happens to the total resistance of the circuit when resistors are connected in parallel circuits

A

The total resistance is less than the resistance of the individual resistors because there are not more paths for the current

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31
Q

What is the relationship between potential difference and current?

A

they are directly proportional (because the resistance stays the same)

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32
Q

What does a potential difference and current do to a filament lamp?

A
  • Causes current to flow through it
  • Causes the filament to heat up and glow
    (the greater the potential difference, the more current flows and the hotter and whiter the filament gets)
33
Q

What happens to a filament’s resistance as it heats up?

A

It increases, meaning the potential difference changes and the current does not change by the same percentage (as the two variables are not in direct proportion)

34
Q

What happens to a diode’s resistance?

A

A diode has a low resistance if the potential difference is in one direction but a very high resistance if the potential difference is in the opposite direction and so this means the current only flows in the one direction

35
Q

How does a light dependant resistor’s resistance work?

A

It has a high resistance in the dark but the resistance gets smaller when the light intensity increases

36
Q

How do Thermistor’s resistances work?

A

High resistance in low temperatures but as the temperature increases the resistance decreases (inversely proportional)

37
Q

How do you investigate resistance in a series circuit?

A
  • Set up a circuit with a resistor and an ammeter in the loop and a voltmeter outside the resistor
  • Use a power pack that is able to change voltages
  • Set it to lowest voltage and write down ammeter and voltmeter readings
  • Repeat this for several different voltages (max 6V)
38
Q

What happens to energy when current passes through a resistor

A

Energy is transferred because electrical work is done against the resistance - the energy is transferred by heating and the resistor becomes warm

39
Q

Give examples of where is the heating effect useful and not useful?

A

Useful- electric heater or kettle

Not useful- computer and plugs etc (because useful energy is being dissipated into the atmosphere as thermal energy)

40
Q

How does a resistor work?

A

As electrons pass through a lattice of vibrating positive ions, they collide, making it hard for them to pass through, so increases the electrical resistance

41
Q

How do you reduce resistance?

A
  • Use low resistance metals for wiring (e.g copper)
  • Make thicker wires
  • Using cooling metals so lattice ions are not vibrating as much
42
Q

Why is lower resistance in wires important?

A

It means that less energy is transferred by heating (because there is no work against the resistance) and less energy is dissipated?

43
Q

How do you calculate the energy transferred?

A

Current x potential difference x time

44
Q

What is power?

A

The energy transferred per second (1 Watt is a transfer of 1 joule per second)

45
Q

How do you calculate power?

A

Energy transferred / time taken

46
Q

What are the two equations for electrical power?

A 
P = I x V 
P= I x I x R
47
Q

In a battery-operated fan, where will the energy go?

A
  • Some of the energy in the battery will be transferred through electricity to the motor, into kinetic energy
  • Heating the wires, motor and surroundings
48
Q

What is mains electricity used for?

A

Appliances that use a large amount of power

49
Q

What is the national gird and how does it work?

A
  • The national grid is the network of wires and cables in which electricity is carried through people’s homes.
  • It comes from the power station where energy is transferred from a store of kinetic energy (such as a turbine) by electricity - then moving to the national grid
50
Q

Give an example of how transferred energy is useful in a home?

A

The motor in a washing machine drum transfers energy (from electricity) to kinetic energy in the washing machine drum

51
Q

What is direct current?

A

The negative and positive terminal of cells and batteries as the direction of the movement of charge stays the same

52
Q

What is alternating current?

A

How mains electricity is produced by generators that rotate causing the current to keep changing.

53
Q

How does the voltage change in an alternating current?

A

The voltage increases to a peak voltage then decrease to zero. It then increases to a peak in the opposite direction before decreasing back to zero - it then repeats (in the UK its 50 cycles per second or 50 Hz, the voltage is on average 230 - same as direct)

54
Q

What does a kettle with a power rating of 3kW transfer in joules?

A

3000 joules of energy per second (from the mains electricity supply to a store of thermal energy in the water)

55
Q

What is a circuit breaker?

A

They are an alternative to fuses. They detect a change in the current and safely switch off the supply

56
Q

Give 2 advantages of circuit breakers

A
  • Once a fault is fixed, it can be switched back on again, whereas a fuse has to be replaced
  • Some types work very quickly and so can save lives whereas a fuse takes time to melt and will not prevent you from getting a shock if you touch a live wire
57
Q

What do insulators collect?

A

Charge

58
Q

Give two examples of insulators?

A

Plastics, Acetate and Polythene (the charge cannot flow from them into another material)

59
Q

What happens when you rub an acetate rod with a dry duster?

A

Some of the electrons move from the rod to the duster and the duster gains a negative electric charge, leaving the acetate rod with a positive charge

60
Q

What happens with you rub a polythene rod with a dry duster?

A

Electrons move from the duster to onto the polythene rod and the opposite situation of the acetate rod happens

61
Q

What happens between rods that have different charges and rods that have the same charge?

A

Different- a force of attraction

Same- repel each other

62
Q

How does static electricity work?

A

When something (for example hair strands) has the same charge. The charge is not able to flow away to the surroundings - since they all have the same charge, they repel each other.

63
Q

What causes an induced charge and how?

A

When a charged object is brought close to a neutral object, it causes an induced charge by attracting like charges or repelling, causing the 2 surfaces to have opposite charges so attraction will occur

64
Q

What causes an electric shock?

A

If something has built up a charge, and then is attached to the Earth (opportunity for it to flow), the item will ‘discharge’ which can cause a shock

65
Q

Why does static electricity build-up in clouds?

A

Due to the friction between particles of ice or water moved by air currents

66
Q

What happens when the static charge in a cloud is large enough?

A

The charged particles travel through the air between the cloud and the Earth causing lightning and thunder

67
Q

How is the danger of lightning made safe?

A

In order to discharge the cloud, buildings are earthed by having lightning conductors made of thick metal running from their tops to the into the Earth

68
Q

What does ‘discharge’ or ‘earthed’ mean?

A

The process of removing or losing charge

69
Q

Why are sparks dangerous?

A

There is fuel vapour that could ignite which can be a problem for refuelling aircraft which often become charged when flying through the air

70
Q

How do aircraft prevent sparks?

A

To prevent a spark between a fuel pipe and an aircraft, a ‘bonding line’ is connected to discharge the aircraft before refeulling commences

71
Q

How are people discharged before filling up their car at a petrol station?

A

When you open the pump in your car, the metal of the car makes you earthed so the fuel pipe doesn’t ignite

72
Q

Give two uses of static electricity

A
  • Insecticide sprayers- have electrodes on the spray nozzle and charge the droplets which spread because they repel and stick on the plant because of induction. The spray is now all over the plant
  • Defibrillators - a build-up of charge on paddles and discharges through the heart to restart it
73
Q

What is a force field?

A

The volume of space around an object in which another object can experience a force

74
Q

What is the field around a magnet called?

A

A magnetic field that will allow a magnetic material to feel a force from the magnet if it is inside this field

75
Q

What does a charged object have around it?

A

A force field called an electric field (or electrostatic field) and if another charged object is placed in this field, it will experience a force

76
Q

What is point charge?

A

It is where the charge is concentrated in a single point of an electric field

77
Q

What do the field lines represent?

A
  • they show where the field is strongest (which is where the field lines are closest together
  • show the direction of the force on a charge in the field
  • start on a positively charged object for example the point charge and end on a negatively charged object and if there is only one object they keep going becoming more widely spaced
78
Q

How do you know where an electric field is stronger?

A

The field lines are more concentrated and close together

Science (23 decks)

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