Friday, 5 September 2014

EMF and internal resistance Questions


                 EMF and internal resistance

1. Explain what is meant by electromotive force (e.m.f.).

2. Explain what is meant by internal resistance.

3. Give one advantage of a battery having some internal resistance.

4. Draw a diagram to how the potential varies around the circuit shown in the diagram.

5. Explain what happens to the output potential across the terminals of a cell with some internal resistance as the current from it is increased.

6. Explain what happens to the output potential across the terminals of a cell with some internal resistance when the external resistor (R in the diagram) is reduced.

7. A cell of e.m.f. 2.5 V and with an internal resistance of 0.2Ω is connected in turn to external resistors of 10Ω and then 1Ω. For each value of the external resistor calculate:
(a) the current in the circuit
(b) the potential difference across the terminals of the cell
(c) the power loss inside the cell

8. A digital voltmeter with resistance of 10 MΩ reads 1.30 V when connected across the terminals of a cell. When the same meter is connected across a resistor of 20Ω that has been connected in series with the cell the voltmeter reads 1.25V.
Explain the difference between these two readings and calculate:
(a) the current in the external resistor
(b) the internal resistance of the cell