Which materials carry electricity
Chemistry · Key Stage 2 · The School
Make a loop of battery, bulb and wires, then cut one wire and leave two loose ends. Touch the ends to a material. If the bulb lights, the material completed the circuit and it is a conductor. If nothing happens, check that the loop works and that the ends touch the material itself. If the bulb still stays off, the material is an insulator. The bulb is the answer.
Metals conduct: copper, steel, aluminium. So does the graphite in a pencil, which is not a metal. Plastic, wood, glass, rubber and dry paper do not. Sorting a tray of objects this way is quicker than arguing about them, and it produces a list you can actually use when choosing a material.
The copper carries the electricity because it conducts. The plastic sleeve stops it going anywhere you did not intend, including into you. One material does the job and the other prevents the job happening in the wrong place — both are chosen from the same test.
The materials that carried heat well in the last lesson are largely the ones lighting the bulb now. That is not a coincidence: in metals the same loosely-held electrons are free to move, and they can carry either energy or charge through the material.
Suppose a class tests a paper clip that has a coat of coloured plastic. Pupils predict first. Steel is a metal, so they expect the bulb to light. Test 1: they touch both loose ends to the coat. The bulb stays off. Is the clip an insulator? Not yet. A gap anywhere in the loop would keep the bulb dark too. Test 2: they touch both loose ends to a plain steel clip. The bulb lights, so the loop works. Now only the coat is different. Test 3: they find an old clip with the coat chipped away at two spots, and touch the bare steel. The bulb lights. So steel is a conductor, a material that lets electricity pass easily. The plastic coat was the gap. Plastic is an insulator, a material that does not let electricity pass easily. This clip is built like a wire, with a metal inside a plastic sleeve.