Which law states that energy cannot be created or destroyed, only transformed?

• A. Law of Thermodynamics
• B. Law of Conservation of Energy
• C. Law of Conservation of Mass
• D. Law of Entropy

Answer: (B)

Energy cannot be created or destroyed; it can only change from one form to another. This means that in any process, the total amount of energy in a closed system stays the same, even though it might appear in different forms. For example, a swinging pendulum shifts energy between height (gravitational potential) and motion (kinetic) as it swings, but the sum of potential and kinetic energy remains constant. Similarly, a power plant transforms chemical or nuclear energy into electrical energy, which can become light, sound, or heat, yet the overall energy count is preserved.

This idea is captured by the law that describes energy conservation. It’s different from the law about mass, which concerns mass itself rather than energy, and from entropy, which deals with disorder and the direction of processes. The broader set of ideas in thermodynamics also includes energy conservation, but the specific principle here is that energy is conserved, only transformed.