level: Electrical sources and internal resistance
Questions and Answers List
level questions: Electrical sources and internal resistance
| Question | Answer |
|---|---|
| what is e.m.f | electromotive force the voltage measured across the terminals of supply when no current is being drawn |
| what is emf measured in | Volts |
| what is internal resistance | the resistance of the material that makes up a cell |
| what is the symbol for internal resistance | r (small r) |
| what is internal resistance measured in | ohms |
| what is an ideal supply | an electrical supply that has no internal resistance |
| what is meant by lost volts | the potential difference across the internal resistance |
| what is t.p.d | terminal potential difference the energy transferred to each coulomb of charge passing through the supply when a current is being drawn |
| is the terminal potential difference usually higher or lower than the e.m.f | lower |
| what is the formula for e.m.f | e.m.f = t.p.d + Ir |
| what is the formula for lost volts | lost volts = Ir |
| what is the relationship between t.p.d and current | as current increases, t.p.d decreases |
| when do you get maximum terminal potential difference in a cell | when current is 0 |
| when there are no lost volts in a cell what happens to t.p.d | it becomes equal to the e.m.f of the battery |
| how do you find the e.m.f of a battery from a t.p.d against current graph | find the y intercept |
| what is an open circuit | a circuit where there is no current flowing |
| what is meant by short circuit | when two wires connect directly across a component and the current flows through the short rather than through the component |
| what is the resistance of a short circuit | zero or very little |
| what is short circuit current | the maximum current a battery can deliver when external resistance of the circuit is zero |
| how do you find the internal resistance from a voltage against current graph | take the negative of the gradient |