How is frequency defined in physics?

Frequency in physics refers to the number of occurrences of a repeating event per unit of time, typically measured in hertz (Hz), which indicates cycles per second. In the context of electromagnetic waves, frequency specifically relates to how many times the wave completes a cycle – changing direction and returning to its starting point – within one second. This concept is crucial as it directly influences the properties of the wave, such as energy and wavelength.

Electromagnetic waves, for instance, can be described by their frequency: higher frequency waves oscillate more times per second and generally carry more energy, while lower frequency waves oscillate fewer times and carry less energy. Thus, defining frequency as the number of times per second an electro-magnetic wave can change direction accurately captures the fundamental characteristics of wave behavior in physics.

The other options present different physical concepts that do not accurately describe frequency. For example, measuring force applied per area refers to pressure, and total energy emitted from a source is a different aspect of wave behavior, often related to luminosity or intensity rather than frequency. The distance traveled by a wave in one cycle relates more closely to wavelength rather than frequency, further emphasizing the specificity of how frequency is defined in relation to wave movement.