Apparatus:

Puzzle box labelled XY, Lab power supply unit, 2 x digital meters, Rheostat, Wires.

Procedure:

1. Set the power supply to 6V.

2. The puzzle box labelled XY contains a diode, aresistor and another resistor connected together in one of the following ways:

3. Set up a circuit to measure the current flowing from X to Y for potential differences between 0V and 5V.

4. Reverse the power supply connections and obtain current values for potential differences down to -5V.

5. Draw a current against voltage graph for the puzzle box for potential differences between –5V and +5V.

6. Draw the circuit diagram of the set up you have used.

7. Use your graph to identify / calculate:which combination of A, B, C or D is correct and the values of resistances R1 & R2 (remember that one of them is).

Explain how you obtained your answers to part 7.

9. Add to your graph the curves that you would have expected to have obtained from the other three possible combinations.