Comparing Waves You Can See

By the end of this lesson, you will be able to compare the amplitude, frequency, and wavelength of transverse waves, including the waves in the electromagnetic spectrum.

Picture two friends holding a jump rope on a Texas playground. One friend flicks her wrist up and down, and a hump travels along the rope to the other end. The rope itself never moves sideways down the field, but the energy does. That is a transverse wave, a wave in which the material moves up and down while the energy travels forward, at a right angle to the shaking.

Three measurements describe that rope wave. Amplitude is the height of the wave from its resting middle line to the top of a crest, and it tells you how much energy the wave carries. A hard flick makes tall humps with large amplitude; a gentle flick makes short humps with small amplitude. Wavelength is the distance from one crest to the next crest, measured in meters. Frequency is the number of complete waves that pass a point each second, measured in hertz. If your friend shakes the rope faster, more waves pass each second, so the frequency goes up and the wavelength gets shorter. Frequency and wavelength work like a seesaw: when one rises, the other falls.

The electromagnetic spectrum is the whole family of waves that includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. All of them are transverse waves that travel at the speed of light, but they differ in wavelength and frequency. Radio waves have the longest wavelengths and lowest frequencies. Gamma rays have the shortest wavelengths, highest frequencies, and carry the most energy.

Visible light sits in the middle, and even inside it red light has a longer wavelength than blue light.

Try it: if a red light wave and a blue light wave both travel at the same speed, which one has the higher frequency?