Physics Electricity

Kirchoffs First Law

Due to con servation of charge, the sum of the currents leaving a point is the same as the sum of the currents entering that point because charge is conserved

Electric Current

Flow of negative charged particles - charge carriers

Electrons

negative to positive

Convential current

positive to negative

Quantised

The net charge of any particle or object has to be a multiple of e

Examples of electric currrent

Flow of electrons inside a metal

Flow of ions in an electrolyte

Current in series

Stays the same at each point

Current in parallel

Splits down each strand

Charge carrier density

the number of free charge carriers per unit volume of a material

Drift speed

Speed with which electrons will move down a wire

What is current proportional to?

Current is directly proportional to drift speed

Ohms Law

As long as temperature remains constant, voltage and current are directly proportional to one another

What happens when you heat a conductor

Ion vibrations increase

Resisitance increase

Drift velocity decreases

So current decreases

Charge carrier density

Number of electrons per cubic metre

Definition of a volt

1 volt = 1 joule per coulomb

Electromotive force

Components like batteries provide a force that pushes the current around a circuit

Potential difference

Components like motors that have work done to them by the current

Sum of EMF

Is equal to sum of p.d

Resistance

Increase length - more ions to pass through

Increase area

Decrease resitivity - density of ions

equation for resistant using resitivity

R = pL/A