Grades 3–5 · Machines
How does a switch turn a bulb on?
A flashlight lights when its switch joins a complete conducting path through the bulb and back to the battery. Metal inside its wires allows electric charge to move; the switch controls the route while the battery supplies the energy.
The battery has two connection points called terminals. Connecting them through the wires and bulb allows an electric current: an ongoing movement of charge around the circuit. Closing the switch joins its metal contacts and completes this route. Opening it separates the contacts, leaving a gap that stops the ongoing current.
When the circuit is complete, the battery supplies energy and the bulb transfers energy to its surroundings as light and heat. The bulb does not use up the charge passing through it. Charge movement and energy transfer are different parts of the same explanation.
The open Switch leaves a visible gap between the Battery and Bulb connections. That gap stops ongoing current, so the bulb cannot transfer the battery's energy as light and heat.
The open Switch leaves a visible gap between the Battery and Bulb connections. That gap stops ongoing current, so the bulb cannot transfer the battery's energy as light and heat.
A loose flashlight contact can leave a gap even when its button says on. Moving the parts around changes nothing if their connections stay the same: with a working battery and bulb, every needed contact must complete the path.
About this explanation
Starting knowledge: Follow a connected path and compare an open and closed switch.
Sources
- University of Colorado Boulder PhET — Circuit Construction Kit DC
- OpenStax — Physics section 19.2 Series Circuits