Electric circuits: symbols, components and brightness

A circuit must be complete

Current only flows if there is an unbroken loop from one end of the cell, through the components, and back to the other end. A switch works by breaking or completing that loop. If a bulb does not light, the first question is always “where is the gap?”

Circuit symbols

Scientists draw circuits with standard symbols — a long and a short line for a cell, a circle with a cross for a lamp, a gap with a lever for a switch, a zig-zag or rectangle for a resistor. Drawings must use straight lines and right angles, not sketches of real wires.

Changing brightness

Add more cells and the bulbs get brighter. Add more bulbs in the same single loop and each one gets dimmer, because the same push from the cell is now shared. This pair of facts is the most tested idea in the whole topic.