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An MRI machine and a mobile phone both use electromagnetic waves. A dog whistle and a bass guitar both produce sound waves. Yet these four devices seem completely different. Here's what's strange: the MRI uses waves 10,000 times longer than the phone signal. The dog whistle produces sound 10 times higher in pitch than the bass note. But all four are described by exactly the same four numbers. What are those four numbers, and how do they connect something that shakes a stadium to something that's inaudible to humans?
An MRI machine and a mobile phone both use electromagnetic waves. A dog whistle and a bass guitar both produce sound waves. Yet these four devices seem completely different. Here's what's strange: the MRI uses waves 10,000 times longer than the phone signal. The dog whistle produces sound 10 times higher in pitch than the bass note. But all four are described by exactly the same four numbers. What are those four numbers, and how do they connect something that shakes a stadium to something that's inaudible to humans?
Every wave — whether sound, light, water, or seismic — is fully described by just four properties: amplitude, frequency, wavelength, and period. These are not four ways of describing the same thing; they are four genuinely independent characteristics. Knowing them precisely lets physicists design ultrasound scanners, predict tsunami arrival times, and tune radio antennas — all using the same vocabulary.
Every wave is described by four independent properties: amplitude (energy, loudness), wavelength (spatial size of one cycle), frequency (how many cycles per second), and period (how long one cycle takes). Amplitude and frequency are completely independent — like volume and pitch on a stereo.
Period and frequency are reciprocals: a wave at 5 Hz completes 5 cycles per second, so each cycle takes T = 1/5 = 0.2 s. Wavelength (λ) measures the spatial length of one complete cycle — from one peak to the next. Amplitude (A) measures the maximum displacement from equilibrium; energy carried by a wave is proportional to A² — so doubling amplitude quadruples energy. This is why a loud sound and a quiet sound at the same pitch have the same frequency but very different energies.