Specified practical

Investigation of the current-voltage (I-V) characteristics of a component

The voltage across and the current through a component (eg a filament lamp) can be measured and the results plotted on a graph to show the I-V characteristic of the component. In this practical activity, it is important to measure and observe the voltage and current accurately.

This circuit shows a diode connected to a voltmeter, with a variable resistor, a battery and a milliamps symbol.This circuit shows a diode connected to a voltmeter, with a variable resistor, a battery and a milliamps symbol

Aim of the experiment: To investigate the relationship between current and voltage for a component

Method

  1. Connect the circuit as shown in the diagram above.
  2. Adjust the variable resistor until the voltmeter reads 1 V.
  3. Record the readings on the ammeter and on the voltmeter.
  4. Adjust the variable resistor to increase the voltmeter reading to 2 V.
  5. Record the new readings on the ammeter and the voltmeter.
  6. Repeat steps 4 and 5, increasing the voltage by 1 V each time, until the voltmeter reads 12 V.

Results

An example results table may be:

Voltage (in V) Current (in A)
00
1.000.20
2.000.50
3.000.78
4.001.00
5.001.15
6.001.25
7.001.36
8.001.41
9.001.46
10.001.50
11.001.53
12.001.55

Analysis

Plot a graph of current (y-axis) vs voltage (x-axis), which should look like this.

Graph plotting voltage against current for a filament bulb. Line is an upward curve, that levels out and start to dip and potential difference increase.Graph plotting voltage against current for a filament bulb. Line is an upward curve that levels out and start to dip as potential difference increases

Evaluation

In a filament bulb, the current does not increase as fast as the voltage. Doubling the amount of energy does not cause a current twice as fast.

The voltage is not directly proportional to the current, so the graph is not a straight line. As the current through the lamp increases, the filament gets hotter and has a higher resistance. It is not an ohmic conductor.

Risk assessment

Hazard Risk Control Measures
Hot lamps can burnBurns to the skin from hot lampsDo not touch the lamp whilst the circuit is connected; allow time for the lamp to cool