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Physics > P2 - Electricity > Flashcards

P2 - Electricity Flashcards

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1
Q

What is electric current

A

Flow of an electrical charge which only flows around a closed circuit
Current is in ampere A

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2
Q

What is potential difference

A

The driving force that pushes the charge round
In volts V
Bigger pd = bigger current

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3
Q

What is resistance

A

Anything that slows the current down
Resistance is in ohm

Big resistance = slow current

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4
Q

The size of the current is….

A

The rate of flow of charge

More charge = more current

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5
Q

Equation for charge

A 
Charge = current x time 
Q = I x t
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6
Q

Circuit symbols - look at notes

A

Beep hoop

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7
Q

What is conventional current direction

A

Goes from positive terminal to the negative terminal of the battery /cell

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8
Q

Equation for potential different

A

Potential difference = current x resistance

V = I x R

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9
Q

Factors affecting resistance

A

Length of wire (in either parallel or series circuit)

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10
Q

Why do some wires need a larger potential difference

A

So they can produce more current than others as they have a larger electrical resistance

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11
Q

What do ohmic conductors have

A

Have constant resistors

The resistance of an ohmic conductor doesn’t change with current

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12
Q

At a constant temperature, the current through and ohmic conductor is directly proportional to….

A

The potential difference across it

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13
Q

Key information of filament lamp

A

Charge flows through a lamp and the Lamp heats up, resistance increases to decrease the current so lamp doesn’t overheat

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14
Q

Key information of diode

A

Resistance depends on direction. It will let current flow, but high resistance if direction is reversed

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15
Q

What are current to potential difference graphs

A

Graph to show how current flowing through a component changes as the potential difference across it increases

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16
Q

Current - potential difference graph of ohmic conductor

A

Linear component - both increase at same rate

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17
Q

Current - potential difference graph of a filament lamp and diode

A

Both Non linear (look at notes)

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18
Q

Key information of a light dependent resistor

A

Resistance depends on light intensity
Bright light = resistance falls
Dim light = high resistance
Used for night lights, outdoor lighting, burglar detectors

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19
Q

Key information of a thermistor

A

Temperature dependent resistor
Hot = resistance drops
Cold = resistance increases
Both can be used in sensing circuits to turn on or increase power to components depending on conditions

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20
Q

Key information of series circuits

A

Different components connected in a line between +ve and -ve of power (voltmeters always in parallel)
If you remove one component circuit breaks

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21
Q

Potential difference in series circuit

A

Total potential difference is shared between the components. Always adds up
V1 + V2 = Vtotal etc.

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22
Q

Current in a series circuit

A

Same current flows through all circuits I1=I2=I3

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23
Q

Resistance in a series circuit

A

2 components resistance will add up Rtotal =R1 + R2
Two resistors share total potential difference
PD lower, current lower in resistor
Current same everywhere. New resistor = lower current everywhere
Bigger resistance = bigger share of PD

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24
Q

Key information of parallel circuit

A

Each component is seperately connected (apart from ammeters)
Remove 1 component = little to no consequence

25
Q

Resistor in parallel circuit

A

Adding a resistor decreases total resistance
Both resistors have same potential difference meaning current flow is the same as the potential difference source for each added resistor
This increases current as another loop gives more directions for current to go in
2 resistors = total resistance = less than the resistance of the smallest of the two resistors

26
Q

Potential difference in a parallel circuit

A

All components get full source of potential difference - equal all around so bulbs all same brightness

27
Q

Current in parallel circuit

A

Total current = total of all currents through separate components
Total current into a junction is the same as leaving
If two identical components are parallel then the same current will flow through them

28
Q

Difference of resistors in the circuits

A

Series - new resistor will increase resistance, decreasing current

Parallel - new resistor will increase current, decreasing resistance

29
Q

Name the two main current supplies

A

Alternate current and direct current

30
Q

How are alternate currents produced

A

AC produced by alternate voltages in which positive and negative ends always changing and electrons pass on energy

AC supplies constantly changing direction

31
Q

What is direct current

A

Current always flowing in same direction
Supplied by cells and batteries
Goes from high charge to low charge through series circuit

32
Q

What Are the 3 wires of a cable

A

Neutral wire -blue
Live wire -brown
Earth wire - green and yellow

33
Q

Role of the neutral wire

A

Completed the circuit and carried away current

Electricity normally flows I’m through the live wire and out the neutral. Around 0v

34
Q

Role of the live wire

A

Provides alternating potential different around 230V

35
Q

Role of earth wire

A

Protecting the wiring. Stops appliance casing from becoming live no current unless fault so 0v

36
Q

What’s a fuse

A

A safety device marked with the current it can carry. Normally 3A 5A or 13A

37
Q

What happens if you touch the live wire

A

As your body is at 0V, a large potential difference is produced across your body and a current flows through you

38
Q

Safety features of a cable

A

Switches connected to a live wire - when off, no current through appliance
Fuse is a tube with a wire in it. Current passes through the wire and the wire heats up, if the current exceeds the limit the wire melts and breaks the circuit
If appliance develops fault, mets, part with high voltage will go to the earth wire instead of you
Circuit breakers like fuses - detect change in current and switch off supply (quicker and no replacement unlike fuse)

39
Q

Energy is transferred between stores electrically by

A

Electrical appliances

40
Q

Why does a moving charge transfer energy

A

Because the charge does work against the resistance of the circuit

41
Q

Electrical appliances are designed to…

A

Transfer energy to components in the circuit when a current flows

42
Q

What happens when current passes through a resistor

A

Energy is transferred because electrical work is done against the resistance. Energy transferred by heating and resistor becomes warm -> why circuits always warm as they all have some form of resistor

43
Q

How can resistance in circuits be reduced

A

Using wires made from metals with low resistance like copper
Or thicker wires = lower resistance
Decreased by coding metals so lattice ions aren’t vibrating as much

44
Q

What happens inside a resistor

A

Electrons(the current) flow through the lattice of vibrating ions, and they collide with the ions - more collisions they make, harder it is for them to pass through.
When electrons collide with ions they transfer energy to the,

45
Q

Transfer of energy examples
Kettle
Handheld fan

A

Kettle transfers energy electrically from the mains AC supply to the thermal energy stores inside the kettle

Energy transferred from battery of a handheld fan to the kinetic energy store of a fans kotor

46
Q

Equation for efficiency

A

Efficiency = useful energy output/total energy output

No appliance transfers all energy usefully
Higher current = more wasted energy

47
Q

Total energy transferred depends on

A

How long the appliance is on for, and it’s powerful

48
Q

What’s the power of an appliance

A

It’s the energy transferred per second

49
Q

Equation for energy transferred

A

Energy transferred = power(W) x time(s)

E = Pt

50
Q

What’s a power rating

A

Maximum safe power that an appliance can operate at

Tells you maximum amount of energy transferred between stores per second

51
Q

Energy is supplied to the….

A

Charge at the lower source

Charge gives up this energy when it ‘falls’ through any potential drops in components elsewhere in the circuit

52
Q

Equation for energy transferred

A

Energy transferred = charge flow (C) x potential difference

53
Q

What happens if a battery has a large potential difference

A

It will supply more energy to the circuit for every coulomb of charge which flows round it, as the charge is raised up ‘higher’ at the start

54
Q

Equation for power

A

Power (W) = Potential difference x current (A)
P = VI
Or power = current squared x resistance

55
Q

What is the national grid

A

A giant web of wires that covers all of Britain
Supplies electricity from power stations to homes
Giant system of cables and transformers that connect power stations to consumers

56
Q

When are there Peak in demands of electricity

A

Morning, when it’s dark or cold and when people come home from work/school

57
Q

Why does the national grid use high PD and low current

A

To transmit lots of power, you need either a high pd or current.
However, high current = lose loads of energy through waste
Cheaper to boost pd
Increasing pd decreases current, decreasing energy lost > more efficient way

58
Q

What do transformers do

A

Step up the pd as it leaves the power stations, but step down the pd to a safe level when given to consumers

Physics (7 decks)

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