Electricity in the home - AQA GCSE Physics P5

Van der Graaf generator

an electric field is formed when electrons move from the dome so a force is applied -> the insulating belt turns to charge the dome -> sparks are formed when an object is within the electric field

thermistor

resistor whose resistance reduces with heat

LDR

light dependent resistor, resistance decreases with light

electrons are

negatively charged particles

protons are

positively charged particles

when an atom has more electrons than protons, it is

negatively charged

electric fields

an area around an object where it can experience a force

ways to prevent electric shocks (4)

- wear protective clothing made from insulating materials
- avoid friction
- no water
- don't touch conductors if they are in contact with a running power source

cell

pushes electrons

wire junction

connects wires at splits in a circuit

heater

converts electric energy to heat

LED

Light emitting diode, emits light when current flows

fuse

melts to break circuit if there is too much current flowing

how does the amount of cells affect current?

more cells = higher current

how does the amount of bulbs affect current?

more bulbs = lower current
more components increases resistance to it's harder for electrons to flow around the circuit

Ohm's law symbol equation

R = V/I

2 types of electricity

static and current electricity

charge

- causes objects to experience a force when in an electric field
- represented by Q
- measured in Coulombs (c)

when an atom has more protons than electrons, it is

positively charged

electrostatic forces

forces of repulsion or attraction between particles

same charges...

repel/experience forces of repulsion

opposite charges...

attract/experience forces of attraction

what is the relationship between charge and electrostatic forces?

greater charge = greater electrostatic forces

what is static electricity?

stationary charge that builds up on an object

how are sparks formed?

when an electric field is too strong, electrons are pulled out of it and collide with other air molecules to balance charges, making sparks

which direction to field lines go in?

direction of the force depending on the charge (away from centre if positive, towards if negative)

what does the space between field lines represent?

the strength of the force (lines closer = force stronger)

what is the relationship between forces and an object's distance from an electric field?

the further an object is from a field, the weaker the forces are

discharging

the movement of charge to balances charges where there is a potential difference

current electricity

continuous flow of electricity in a complete circuit with a power supply

current

- rate of charge flow
- repesented by I
- measured in Amps (A) or Coulombs per second (C/s)

current equation word equation

current (A) = charge (C)/time (s)

current symbol equation

I = Q/t

battery

2+ cells

wire

connects circuit components

switch

stops/starts flow of current by breaking circuit

bulb/indicator

emits light when current flows through it

ammeter

measures current

voltmeter

measures potential difference

fixed resistor

limits current

variable resistor

limits current but resistance can be changed

diode

only allows current to flow in one direction
*symbol has no arrows going out! (no other pic option)

where should an ammeter be placed in a curcuit?

anywhere because current is the same everywhere in a series circuit

Ohm's law word equation

resistance (Ohms) = potential difference (V)/current (A)

potential difference equation

potential difference (V) = energy or work done (J)/charge (C)
V = E/Q or V = W/Q

how does the number of cells affect potential diffference across a bulb?

more cells increases potential difference as they provide more electrical potential energy

factors that affect resistance (5)

- material's thermal conductivity
- potential difference
- current
- thickness of material
- length of material

method for resistance required practical

1. create circuit with D.C. power supply, switch, ammeter, ruler with resistance wire and voltmeter connected to it in parallel
2. connect clip to resistance wire
3. record ammeter and voltmeter readings
4. move crocodile clip 10cm
5. take readings again
6. repeat steps 2-5, increasing wire length by 10cm each time
7. calculate resistance from results
8. create graph for resistance against wire length

what is the independent variable for the resistance required practical?

length of wire

what is the dependent variable for the resistance required practical?

resistance

what are some controlled variables for the resistance required practical?

wire (temperature, thickness), voltage

what are some potential safety concerns for the resistance required practical and how can they be avoided?

- burns or electric shocks from hot wire, so don't touch it
- fire if wire is too far

what are the 2 types of circuits?

series and parallel

series circuit

a circuit with only one path for current to flow through

current in a series circuit is...

the same everywhere/through each component

potential difference in a series circuit is...

shared between components

resistance in a series circuit is...

the sum of all resistances
Rt = R1 + R2

parallel circuit

a circuit with multiple paths in parallel to eachother for current to flow through

current in a parallel circuit is...

the sum of currents through each component

what happens to current in a parallel circuit at a wire junction?

current splits

potential difference in a parallel circuit is...

the same everywhere/across all components

resistance in a parallel circuit is...

lower than the resistance of the smallest resistor

what happens to resistance in a parallel circuit as more branches are added and why?

resistance decreases as there are more paths for current to flow through

D.C.

direct current, current only flows in one direction and is usually low

A.C.

alternatiing current, current constantly switches direction as electrons collide and bounce back

mains electricity

- energy supply to buildings from the national grid
- A.C.
- 50Hz frequency and changes direction 50 times a second
- average 230V, maximum of 325V

oscilloscope

instrument that shows how voltage varies over time on a graph

peak voltage

voltage between 0V and the top of a wave

frequency

number of waves past a fixed point per second

period

time taken for 1 full cycle of the waveform

what are the 3 cables within plugs in the UK?

live, neutral and earth

live wire

brown, carries A.C. potential difference from the mains supply, dangerous

neutral wire

blue, completes circuit to the live wire, at or near 0V

earth wire

green and yellow striped, safety wire which directs current into the ground if there is a fault with the live wire, should have no voltage

dangers of mains electricity

if the live wire came loose and touched metal casing, it would become electrified and pose a risk of electrocution
the earth wire is a low resistance path into the ground to direct current away, causing a surge of current to melt the fuse and break the circuit so the connected appliance is safe to touch
the live wire can cause shocks even if the device is switched off