What is a battery in today's terms?

• A. any device that maintains a constant voltage by keeping two collections of positive and negative charge separate
• B. a device that creates sound vibrations to power speakers
• C. a device that stores energy by elastic potential
• D. a device used to measure temperature

Answer: (A)

Batteries store chemical energy and convert it into electrical energy by driving reactions that create a difference in charge between two terminals. The key idea is that opposite charges are kept apart inside the device, producing a voltage that can push current through a circuit when connected.

Among the options, the one describing maintaining a separation of positive and negative charges to create a voltage between terminals best matches how a battery powers devices. The other choices describe sound production, storing energy as elastic potential, or measuring temperature—none of which capture how a battery provides electrical energy. Remember that battery voltage can change as it discharges, but the essential feature is energy storage that establishes a voltage between the terminals.