6 electricity

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