Which component represents the energy source in a circuit diagram?

• A. Light bulb
• B. Resistor
• C. Switch
• D. Battery

Answer: (D)

Energy is supplied to a circuit by the source that creates the driving emf. In a simple diagram, the energy source is the battery, which provides the electrical energy that pushes charges around the circuit. The light bulb acts as a load, converting electrical energy into light and heat. The resistor is a passive element that limits current and drops voltage. The switch only controls whether the circuit is complete, not whether energy is produced. So the component that represents the energy source is the battery, the source that powers the circuit.