Electromagnetic signals are described by their frequencies. Which option correctly names the property used to describe these signals?

• A. Amplitude
• B. Phase
• C. Wavelength
• D. Frequency

Answer: (D)

The key idea is that the property used to describe how often an electromagnetic signal repeats each second is frequency. Frequency, measured in hertz, is the rate of oscillation of the electromagnetic fields — how many cycles occur per second.

Amplitude describes how strong the signal is, not how fast it repeats. Phase tells you where you are in a cycle at a given moment, not the repetition rate. Wavelength is the distance the wave travels during one cycle, and while it relates to frequency through the speed of light (lambda = c/f in vacuum), it describes a spatial property rather than the temporal repetition rate. So the term that best describes how often the signal occurs per second is frequency.