a) Internal resistance

• define terminal pd

• the pd measured across the terminals of an emf source

• define internal resistance

• the resistance within an emf source

• explain the concept of internal resistance and lost volts

• when there is current in an emf source

• the emf source transfers chemical energy to the electrical store of the charge carriers

• some chemical energy is dissipated into thermal energy

• internal resistance

• lost volts

• describe the relationship between terminal p.d. and e.m.f.

• terminal pd < emf

• emf = terminal pd + lost volts

• when current is 0A → emf = terminal pd

• state the formula for lost volts

• lost volts = Ir

  • lost volts (V) = current (A) × internal resistance (Ω)

• state the two formulae for emf

• ε = I(R + r)

  • emf (V) = current (A) × (external resistance (Ωs) + internal resistance (Ω))

• ε = V + Ir

  • emf (V) = terminal pd (V) + (current (A) × internal resistance (Ω))