P2-Electricity

current

A flow of electric charge.

(like the rate of it)

potential difference

The driving force that pushes the charge around

resistance

A material's opposition to the flow of electric current.

greater resistance means...

smaller current (less flow)

ammeter

measures current

always in series

Voltmeter

measured potential difference

always in parallel

RP- Resistance

need: voltmeter, ammeter, metre ruler, wire, battery, 2 crocodile clips

1) attach 1 crocodile clip to 0cm on wire, other to 10cm

2) close switch, record current and pd

3) open switch, move crocodile clip down 10cm and measure again

4) repeat, use equation and plot the graphs

RP- current and pd (IV characteristics)

need: battery, voltmeter, ammeter, variable resistor, component (diode, lamp, resistor)

1) vary variable resistor which alters the current and pitential difference across the components

2) take readings from the voltmeter and the ammeter to see how the potential diference changes ascurrent does

3) swap wires sides connected to battery to reverse current's direction

4) repeat measurements

5) graphs

IV characteristics graphs

resistor

/ straight line

(directly proportional)

lamp

mid graph

(as current increases, temperature of the lamp increases, so the resistance does too)

diode

steep curve hill in first quadrant

(current only flows in one direction when using a diode and it heats up)

LDR

light dependent resistor

bright=resistance falls, so it works

dim=resistance increases, so it doesnt work

good for automatic night lights, burglar detectors...

thermistor

A resistor that changes its resistance with a change of temperature.

hot= resistance decreases

cool= resistance increases

(good for temperature detector, thermostats)

sensing circuits

Can be used to turn on or increase the power to components depending on the conditions that they are in

series circuit

all components connected in a line

disconnect 1, the whole circuit fails

PD is SHARED

CURRENT is SAME

resistance and pd can be added up

parallel circuit

components can be branched, multiple paths

one disconnection wont affect others greatly

PD is SAME (same P)

CURRENT is SHARED

RP- Resistance in series vs parallel

series: 1) build ammeter, battery, resistor. note PD of battery for equation later.

2) measure current to calculate resistance with PD too

3) add resistor in series

4) repeat 2 and 3 until 4 resistors have been used and make graphs

parallel is the same, but you add the resistors in parallel

results of resistance in series vs parallel practical

in parallel:

add resistors->current increases->resistance decreases (because theres now more than one path for the currewnt)

series:

current decreases and resistance increases

AC

alternating current

when current is constantly changing directions, produced by alternating voltages

e.g. UK mains supply

Mains supply

AC

230V

50Hz

DC

direct current

current flowing in one direction

e.g. cells, batteries

3 wires in a plug name and colour

live - brown

neutral - blue

earth - yellow and green

Live wire

brown

carries alternating potential difference from the mains

can shock you

230V

Neutral Wire

blue

completes the circuit.

carries away current

0V

Earth Wire

green and yellow

stops casing from becoming live

carries no current unless faulty

0V

what is the national grid?

A system of cables and transformers linking power stations to consumers

journey of electricity

electricity is generated in power stations

step up transformer increases the voltage to minimise energy loss

transports between pylons via the wires

step down transformer decreases voltage to ensure its safe to use

transported to homes