Practical: A simple electric circuit
An electric circuit is a path made of a source, a consumer (lamp, motor), a switch and conducting wires joining them. Two conditions are needed for current: there must be a source and the circuit must be closed. With the switch open the circuit is broken and the lamp stays off; with it closed current flows and the lamp lights. Electric current is the orderly motion of charged particles. By convention the direction of current in the external circuit is from the source’s positive (+) pole to its negative (–) pole (in metals the electrons actually move the other way). Materials that pass current are conductors: metals (copper, aluminium, iron), graphite, salt water, the human body. Those that do not are insulators: rubber, plastic, glass, dry wood, porcelain, dry paper. Wires are a metal conductor covered by an insulating sheath: the sheath keeps current from passing into our body. Safety: use only a 1.5–4.5 V battery for experiments; never experiment with a mains socket (220 V); never join the two poles of a battery directly by a wire (a short circuit heats the wire and the battery).
Assembling a circuit: with a 1.5 V battery, a lamp (with holder), a switch and 3 insulated wires assemble a circuit. Observe with the switch open and closed. Then connect pieces of copper, iron, plasticine, paper and rubber between the wires and record in a table with “+” or “–” whether the lamp lights. Safety: work only with a battery; open the switch before touching connections; mind the sharp wire ends; keep away from sockets.