Introduction and key concepts

Introduction

Waves occur frequently in nature. The most obvious examples are waves in water, on a dam, in the ocean, or in a bucket. We aremost interested in the properties that waves have. All waves have the same properties, so if we study waves in water, then we can transferour knowledge to predict how other examples of waves will behave.

What is a transverse wave ?

We have studied pulses in Transverse Pulses , and know that a pulse is a single disturbance that travels through a medium. A wave is a periodic, continuous disturbance that consists of a train of pulses.

Wave

A wave is a periodic, continuous disturbance that consists of a train of pulses.

Transverse wave

A transverse wave is a wave where the movement of the particles of the medium is perpendicular to the direction of propagation of the wave.

Investigation : transverse waves

Take a rope or slinky spring. Have two people hold the rope or spring stretched out horizontally. Flick the one end of the rope up and down continuously to create a train of pulses .

1. Describe what happens to the rope.
2. Draw a diagram of what the rope looks like while the pulses travel along it.
3. In which direction do the pulses travel?
4. Tie a ribbon to the middle of the rope. This indicates a particle in the rope.

   

5. Flick the rope continuously. Watch the ribbon carefully as the pulses travel through the rope. What happens to the ribbon?
6. Draw a picture to show the motion of the ribbon. Draw the ribbon as a dot and use arrows to indicate how it moves.

In the Activity, you have created waves. The medium through which these waves propagated was the rope, which is obviously made up of a very large number of particles (atoms). From the activity, you would have noticed that the wave travelled from left to right, but the particles (the ribbon) moved only up and down.

When the particles of a medium move at right angles to the direction of propagation of a wave, the wave is called transverse . For waves, there is no net displacement of the particles (they return to their equilibrium position), but there is a net displacement of the wave. There are thus two different motions: the motion of the particles of the medium and the motion of the wave.

The following simulation will help you understand more about waves. Select the oscillate option and then observe what happens.

Peaks and troughs

Waves have moving peaks (or crests ) and troughs . A peak is the highest point the medium rises to and a trough is the lowest point the medium sinks to.

Peaks and troughs on a transverse wave are shown in [link] .

Peaks and troughs

A peak is a point on the wave where the displacement of the medium is at a maximum. A point on the wave is a trough if the displacement of the medium at that point is at a minimum.

Amplitude and wavelength

There are a few properties that we saw with pulses that also apply to waves. These are amplitude and wavelength (we called this pulse length).