key definitions electricity

Internal Resistance

Resistance due to opposition of flow of charge within a source of e.m.f.

ε = I(R+r)

Lost volts

The difference between the terminal voltage and the e.m.f. of a source of e.m.f due to energy being dissipated across the internal resistance of the power source

terminal voltage

The potential difference measured across the battery/power supply when that battery/power supply is connected by a complete circuit to a load (external) resistance. If there is no internal resistance, the terminal p.d. will equal to the e.m.f.

Potentiometer

A potential divider circuit which consists of one length of wire and a sliding connection to alter the ratios resistances of the two sections of wire

Potential Divider

A circuit which allows a user to vary an output potential difference using the principle of shared potential differences given by Kirchhoff's Second Law

Electrical Power

Power is the rate at which energy is transferred, used or transformed, measured in J s-1 or Watts

KiloWatt hour

A unit of energy equal to 1kW of power usage for 1 hour i.e. 1kWh = 1000 x 60 x 60 = 3.6 million joules. Often used to calculate household energy bills

Ampere

1A is equal to 1C of charge passing a point in 1s

Kirchhoff's Second Law

The total e.m.f. around a closed loop circuit is equal to the sum of potential drops (potential differences) around that loop. This is due to conservation of energy.

Potential Divider

A circuit which allows a user to vary an output potential difference using the principle of shared potential differences given by Kirchhoff's Second Law

Coulomb

The amount of charge that passes in 1 second when the current is 1 ampere.

Insulators

An insulator does not conduct electricity, therefore for a perfect insulator, the number density of free charge carriers (n) would be 0 and there would be no current flow. However, for real insulators, n is very small.

Light dependent resistor (LDR)

An electrical component with a resistance that decreases as the light intensity incident on it increases

potential difference

change in potential energy per unit charge between 2 points due to charge doing work on components