Bulb and Diode IV Curves Using a Datalogger


PC, DL128 data logger with low current and voltage sensors, Lab power supply set at 3V DC, mounted 47Ω resistor, mounted silicon diode, 2.5V mounted light bulb, rheostat (variable resistor), wires.


In this experiment you are going to use a data-logger to quickly obtain data for a set of current-voltage (IV) characteristics. The graphs will be displayed on the computer monitor. Please follow the instructions below carefully remembering that computers and their software are stupid!


1. The PC has already been switched on and the data logger and sensors have already been wired up to it. DO NOT SWITCH OFF THE PC OR ALTER THE WIRING.

Switch on both sensors (Press 'ON' buttons). Set the scales to ±5V & ±500mA. Do not alter these scales during the experiment (ignore any messages such as "CHANGE SCALE".

2. Wire up the circuit shown below using the low current and voltage sensors as your ammeter and voltmeter. Adjust the potential divider so that the voltmeter reads about 2.5 volts. The ammeter should read about 50 mA.

Setting up the program:

S1. On the PC double click on the DATADISC PRO icon and wait for the program to load. After a few seconds a screen containing menus should appear.

S2. From the MEASURE menu select "RECORD". The Recording Choice Demon screen should appear.

S3. Click on NEXT. The next screen concerns channels to record from.

Make the x-axis = channel 1 PD/V.

Do not alter anything else (the time selection will automatically deselect itself).

Click NEXT

S4. For all the other screens click NEXT until the final one where you should click FINISH.

Do not alter any of the selections.

S5. A window containing graph axes should now appear. Maximise this window.

Collecting Data:

You are about to collect data.

Once you initiate the computer it will take readings every 0.2 second for a two minute period. You should aim to perform steps 1 to 4 below during this time.

C1. To start the data recording process click on the START icon (looks like a tape recorder) below the menu bar.

C2. Once you have done this use the potential divider to slowly vary the voltage across the

47Ω resistor between 3V and 0V over a thirty second period. You should notice the computer plotting points on its graph during this time.

C3. Now reverse the connections to the power supply so that both meters give negative readings and repeat stage 2.

C4. Finally click on the FINISH icon (looks like a hand).

Displaying & analysing the first set of data:

D1. A choice box appears. Click on "KEEP THIS DATA".

D2. A messy graph appears. Go to the GRAPH menu and choose "SET AXES".

D3. Delete X from the time choice box. Then click "OK".

D4. A clear graph showing how the current through the resistor varies with voltage should now appear.

D5. If the printer is working, you may like to print your graph.

D6. Use your graph to check that the resistance value IS approximately 47Ω. Do this by dividing a voltage value by the corresponding current vale (in amperes).

Displaying and analysing subsequent sets of data:

You are now going to use the above technique with the light bulb & diode.

A1. Disconnect the 47Ω resistor and connect instead to the terminals of the light bulb.

A2. Repeat set up stages, S2 to S5, collecting data stages, C1 to C4 and display stage D1 only.

A3. After clicking "KEEP THIS DATA" you will be presented with a "data information" screen. Click "OK" and click buttons to allow previous files to be overwritten. You should eventually be returned to a messy graph (stage D2 above).

A4. Repeat display stages D2 to D4.

A5. Use your graph to calculate how the resistance of the light bulb varies with voltage.

A6. Repeat stages A1 to A5 for the mounted diode.


Data-logging exploration:

If you have time explore the effects of changing options under the various menus. You should try to find a way of calculating resistance values and displaying how resistance varies with current, voltage or time.

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