EMF and Internal Resistance

• The electrons deliver the energy to the lamp as they pass through it
• Each electron re-enters the battery to be resupplied with more energy
• As each electron passes through a circuit component (the battery or the lamp), energy is transferred. This means that work is done.

• V = WQ can be rearranged as W = QV
• The electromotive force (emf ) of a source of electricity is defined as the electrical energy (W) produced per unit charge (Q) as it passes through the power source.
• W = Q
• is measured in volts

• Internal Resistance- The resistance within a supply of electricity. A cell or bettery, inherent in its design, will resist the flow of electricity through it
• Electromotive Force (Emf)- The energy per unit charge produced by the source
• Potential Difference- The energy per unit charge delivered when the source is connected to a circuit

Power is calculated by multiplying each term in the formula (recall from GCSE that P = IV)

• P = εI = I(IR + Ir) = I^2R + I^2r

The power is therefore made up of two parts:

• The power delivered by the source to the component
• The power wasted in the cell through the internal resistance