Electricity

Electrical Current (definition, units)

The rate of flow of charge, symbol I, measured in ampères, A; normally a flow of electrons in metals or a flow of ions in electrolytes

Electrical Current (equation)

I = ΔQ/Δt = charge transfered (coloumbs) / time (seconds)

Charge of an electron

-1.6×10^-19 (=-e)

Elementry charge

1.6×10¹⁹

Kirchhoff’s 1^st law

At any point in an electrical circuit, the sum of currents into that point is equal to the sum of currents out of that point, electrical charge is conserved

Conventional current

The ‘flow of positive charge’ - it is in the opposite direction to the movement of the electrons in the circuit.

What is meant by ‘mean drift velocity’

The average velocity of the charge carriers due to the applied electric field. It has to be an average because they’re often moving randomly in all directions.

Equation for drift velocity

I = Anev

Current = Cross-sectional area × number density × elementry charge × mean drift velocity

Number density

Number of charge carriers per metre³