Which of the following is not measured by frequency?

• A. Light
• B. Heat
• C. Line Current
• D. Sound

Answer: (B)

Frequency is how many times something repeats per second, and it applies to waves and oscillations. Light is an electromagnetic wave, and its frequency determines its color within the visible spectrum. Sound is a mechanical wave, so its frequency determines the pitch you hear. An alternating current in power lines also has a frequency—the rate at which the current reverses direction each second. Heat, on the other hand, is about energy transfer due to temperature differences and is described by temperature, energy, or power of transfer, not by how often something cycles per second. So heat is not measured by frequency.