Pencil lead resistance characteristics
The resistance of the pencil lead is too large compared to the resistance of a small light bulb, and the divided voltage is small, so the brightness is small.
In fact, the small light bulb is bright, but the brightness is too small to be seen by the naked eye.
1. Reduce the length of the pencil lead in the circuit
2. Increase the voltage
3. Change to a lower power bulb (the smaller the bulb power, the greater the resistance, and the greater the divided voltage)
In the fifteenth century, graphite ore was discovered. People at that time did not know the composition of graphite, so graphite was called black lead. Around 1492, some people in Britain began to use pens made of graphite, called pencils.
It was not until 1779 that scientists knew that graphite was a form of carbon. It is made from graphite ground into powder, mixed with clay, and then poured into two semicircular wooden tubes. Plastic penholders are also available on the market.