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Current
Rate of flow of charge
Equation for electric current
I = Q/t
Where
I is current in amps
Q is charge C
T is time in seconds
1 couloumb
Amount of charge that flows in one second when the current is on amp
Potential difference
Work done per unit charge
V= w/q
Where
V Is potentially difference in V
W is work done in joules
Q is çharge in coulombs
Equation relating potential difference to kinetic energy
W= Ve = ½ m v²
Where
W is work done in joules
V us potential difference in volts
E is the charge of an electron
M is mass of an electron
V is velocity in m s -¹
Power
The rate of energy transfer
P= w/t
Where
P is power in Watts
W is work done in joules
T is time in seconds
For electrical circuits P= V I
Where
P is power in Watts
V us potential difference
I is current in amps
Additionally
P= V²/ R
And
P= I² R
Work done
W = Pt = V I t
How to obtain an I V graph
Set up a circuit with a variable resistor in series with a component and power supply
Add a voltmeter in parallel and an ammeter in series
Vary the resistorand record values
Repeat until you have a full set of readings
Plot and draw a line of best fit
IV Graphs
Ohmic resistor y= x
Filament lamps y= x³
Diode is only positive after 0 as current only flows forward in the forward bias
Ohms law
V = IR
the graph for an ohmic resistor at cinstant temperature is linear and goes through the origin
Factors influencing resitance
Length
Area
Resistivity
Resistivity definition and formula
Resistance encountered inappropriate material that is ine metre long and has a cross sectional area of 1m² measured in ohm metres
R= pL / A
Where
R is resistance
P is resistivity
L is length In m
A is area in m²
To find the resistivity of a wire
Measure a wires diameter using a micrometer nd calculate its cross sectional area
Sry up a circuit with wire power supply ammeter and voltmeter
Record volatgr and current
Calculate resistance using v is IR rearranged
Create a graph of length against resistance
The gradient = p/ a
Multiply the gradient by a to get p
Kirchoffs first law
Sum of currents entering a junction is the same as the sum of currents leaving that junction
Basically charge is conserved
Note 
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