Fix a LED on an approximately 60-70 cm long wire by placing a 100 Ω metal film resistor in front of the anode and making sure an appropriate connection possibility exists to the power supply. You may carry out the experiment with three LEDs just as well, connected in parallel. It is recommended to energise the LED or LEDs by direct voltage. Connect the anode to the positive and the cathode to the negative potential. You will see that the LED gives light continuously. In the next step spin the LED at the end of the twin wire around.  The LED would draw a continuous light circle. In the second case the twin wire line holding the LEDs is connected to alternating current. Our experience will conform with the former sight: the LED lights permanently. However, if you spin the LED on the end of the twin wire line, this time you will be able to observe that the circle drawn by the LED consists of interrupted lines, since the LED lights up only in every half period, and will not be illuminated in the other half. Pending on their colour, the opening voltage level of the LEDs used in the experiments falls between 1.7 and 2.5 V. Readily available voltage sources have typically 1.5 V, or an integer multiple. In other words a single 1.5 V 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

– Wires
– Three different coloured LEDs connected in parallel
– A 100 Ω metal film resistor connected in front of the anode (+) as a preventive lead to protect the LED
– Wires
– a 3-4.5 volts power supply source