Electrical circuit. Switch being held closed (at right) to complete an electrical circuit. Electric current from the battery (upper centre) is flowing through the wires and switch, and the light bulb (at left). The electric current is heating the light bulb's filament, causing it to emit light and heat. If the switch is released, it will open, the circuit will be broken, electric current will cease to flow, and the light bulb will no longer emit light.