Waves

There are different kinds of waves. All waves have one thing in common: they transfer energy from one place to another.
• A wave is a phenomenon in which energy is transferred through vibrations. The wave carries energy away from the wave source. You can see the effect of rope waves if you fix one end of a rope by tying it round a rod and move the other end up and down. A series of crests and troughs can be seen to pass along the rope. Each section of the rope is set into an up-and-down motion by the previous section as the wave passes along the rope.
• The rope is the medium through which the wave propagates. Note that the particles in the rope itself do not move forward with the wave.
• A similar effect is obtained with water waves. A small cork on the water surface will bob up and down (or vibrate) as the wave passes, but will not travel forward with the wave. In this case, water is the medium through which the energy is transmitted.
Types of Waves
1. Transverse waves
2. Longitudinal waves
Transverse waves• Water waves and rope waves are examples of transverse waves. Transverse waves are waves which travel in a direction perpendicular to the direction of the vibrations. If you move the end of a slinky coil from side to side, transverse waves are set up. Light waves and other electromagnetic waves are also transverse waves.
At home you produce transverse waves when you shake the dust from a blanket or rug. Watch closely the motion of your hand, flipping the edge of your blanket, and the waves that are produced.
Longitudinal waves
• Another type of wave is the longitudinal wave. Longitudinal waves travel in a direction parallel to the direction of vibrations.
• If a slinky coil is pushed and pulled at one end, longitudinal waves are set up. Watch the way the compression travels along the coil. The compressed coils themselves do not travel. They just vibrate forward and back. Sound waves are examples of longitudinal waves.
Wave Terms• Some of the terms and quantities used to describe transverse wave motion are as follows:
1. The high points are called crests or peaks while the low points are called troughs.
2. The amplitude is the maximum displacement from the rest position. It is the height of a crest or depth of a trough measured from the normal undisturbed position.
3. The wavelength, l, is the distance between two successive crests or two successive troughs. It is also equal to the distance between any two identical points on successive waves, for example points A and B, and points C and D in figure
4. The frequency, ƒ, is the number of crests (or troughs) that pass a point per second. This is equivalent to the number of complete waves generated per second. Frequency is measured in hertz (Hz). A frequency of 1 hertz means that one wave cycle or one oscillation is completed per second.
5. The period, T, is the time taken to generate one complete wave. It is also the time taken for the crests, or any given point on the wave, to move a distance of one wavelength. T = 1 / ƒ
6. The speed, n, of the wave is the distance moved by a wave in one second. Since the wave crest travels a distance of one wavelength in one period, the wave speed, n = l/T or n = ƒ l
7. In longitudinal waves, the part where the particles of matter are closest together is called the compression. The part where the particles are spread apart is the rarefaction.