L1 - Transverse & Longitudinal Waves

objectives

If you drop a stone into a pond, ripples spread across the surface. The tiny waves carry energy, as you can tell from the movements they cause at the waters edge. But there is no flow of water across the pond. The wave effect is just the result of up-and-down motions in the water.
Waves are not only found on water. Sound travels as waves, so does light. Waves can also travel along stretched springs like those in the experiments next.
These show that there are two main types of waves.

When the end coil of the spring is moved sideways, it pulls the next coil sideways a fraction of a second later... and so on along the spring. In this way, the sideways motion (and its energy) is passed from coil to coil, and a travelling wave effect is produced.

The to-and-fro movements of the coils are called oscillations. When the oscillations are up and down or from side to side like those above, the waves are called transverse waves.
In transverse waves, the oscillations are at right-angles to the direction of travel.
Light waves are transverse waves, although it is electric and magnetic fields which oscillate, rather than any material.

Moving the end coil of the spring backwards and forwards also produces a traveling wave effect. However, the waves are bunched-up sections of coils with stretched-out sections in between. These sections are known as compressions and rarefactions.
When the oscillations are backwards-and-forwards like those above, the waves are called longitudinal waves. In longitudinal waves, the oscillations are in the direction of travel.
Sound waves are longitudinal waves. When you speak, compressions and rarefactions travel out through the air.

On the right, transverse waves are being sent along a rope. Here are some of the terms used to describe these and other waves:
Speed The speed of the waves is measured in metres per second (m/s).
Frequency This is the number of waves passing any point per second. The SI unit of frequency is the hertz (Hz). For example, if the hand on the right makes four oscillations per second, then four waves pass any point per second, and the frequency is 4 Hz. The time for one oscillation is called the period. It is equal to 1/frequency. If the frequency is 4 Hz, the period is 1/4 s (0.25 s).
Wavelength This is the distance between any point on a wave and the equivalent point on the next.
Amplitude This is the maximum distance a point moves from its rest position when a wave passes.

The speed, frequency, and wavelength of any set of waves are linked by this equation:

In symbols:

6.01---Transverse-and-Longitudinal-Waves.docx

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