Current - potential difference graphs II

Objectives:

• Be able to build a circuit to vary, and measure, the voltage and current through a diode.

• Be able to describe the relationship between voltage and current for a diode.

• Know that the resistance of a diode is very large below the threshold voltage, and decreases above the threshold voltage.

Task 1 - Starter

Sketch the following graphs neatly in the front of your exercise book:

    • voltage and current for a resistor

    • voltage and current for a bulb

Make sure you give each graph a suitable title and label both axes appropriately and write a sentence by each to explain how the current changes as the voltage is increased.

Task 2

Your teacher will demonstrate how to build a circuit with a variable resistor to measure the voltage across a diode and the current flowing through it.  Watch carefully - you will need to do this in a minute!

Task 3

Draw the circuit diagram above in your book, and then build the circuit.  Slowly increase the voltage to a maximum of 3.5V, and measure the current flowing at 0.1V intervals.  You will find there is no current flowing at a lot of the low voltages!

When you have finished, turn the diode around in the circuit and test it again.  What do you notice now?

Task 4

Plot a graph of your results:

• use a sheet of A4 graph paper in a landscape orientation.

• make sure current is on the y-axis and voltage is on the x-axis.

• label the axes appropriately, with units, and give your graph a title.

Homework:

Your teacher will give you a sheet*, showing the current-voltage graphs for each of the three components you have investigated.  Match the correct statements to each of the graphs.

*Teacher / technician note: we don't have a digital copy of this at present.  It is in the blue folders with the old year 11 content.

Old resources