Prepare the circuitry on the basis of the connection diagram. Change the LED voltage by one hundredth volts by increasing the resistance in the part of the potentiometer in parallel with the LED. Record the voltage and current levels measured in a tabulated form and present on a graph. The barrier voltage of the LED (VB) can be read from the I-V graph. Pending on their colour, the opening voltage level of the LEDs used in the experiments falls between 1.7 and 2.5 volts. Readily available voltage sources have typically 1.5 volts, or an integer multiple. In other words a single 1.5 volts penlight battery would be insufficient, two is too much. The load bearing capacity of these tiny LEDs is very low, therefore it is definitely necessary to use a preventive lead (switch resistance) to protect the LED which is usually connected to the circuit before the anode.

Implements required for the experiment

– LED
– One 100 Ω metal film resistor as a preventive lead to protect the white LED
– Voltmeter
– Ammeter
– Potentiometer (10 kΩ, linear, multiple revolutions)
– Power supply source
– Wires

The opening voltage for the green LED used here:
VB = 1.85 volts
(VB is the barrier voltage of the LED)

The longer the wavelength of the light emitted by the LED, the larger the opening voltage.