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The Challenge: Make an underwater flashlight



How can we make our own light bulb?

First, a resistor was put in the circuit in series. The resistor was a very long bit of wire that we knew wasn't great at conducting a current. We gradually reduced the length used, then took it out of the circuit when we were sure it was safe.

We tested out which wires glowed the brightest and lasted the longest. We began by using a 50cm (19.7 in.) piece of wire coiled up and gradually reduced the length until it glowed.

The shorter the length, the more brightly it glowed but the more quickly it burnt out. To increase the brightness we used two filaments in the same glass jar.

Filaments in the jar
Filaments in the jar