Waves

            A wave carries energy from one place to another. There are two types of wave : transverse and longitudinal.

            A transverse wave is like a wave along a string or a rope. The energy is being transferred from left to right, but the rope moves up and down. This means that it vibrates at a right angle to the direction of the energy movement. Some examples are water waves, electromagnetic waves and light waves.

            A longitudinal wave is much like a slinky spring. If you move one end of the spring backwards and forwards repeatedly along the direction of it, you will see waves travelling along it. Each part of the slinky oscillates along the line of the spring. Sound waves are longitudinal waves.

            In order to describe waves, there are some terms which are used. These are the peak, the frequency, the wavelength, the amplitude and the speed.

·        One complete wave is from one wave peak to the next wave peak.

·        The frequency, represented by f , is the number of complete waves passing a point in one second. The unit of frequency is hertz, Hz. A frequency of 1 hertz means that one complete wave per second passes a certain point.

·        The wavelength , represented by λ , of a set of waves is the distance from one wave peak to the next wave peak. It is measured in the units of distance such as metres, centimetres and so forth.

·        The amplitude of a wave is the height of its wave peak or the depth of its wave through from the middle. The bigger the amplitude, the more energy the wave carries.

·        The speed of a wave is the distance travelled by the wave peak per second. It is usually measured in metres per second.

All types of waves have certain properties. For example, they can all be reflected. Sea waves reflect off sea walls; sound waves reflect to cause echoes; light waves reflect off mirrors. In order to study the properties of water waves, we must use a ripple tank.

One property, mentioned above, is that they all reflect. If you place a barrier in the ripple tank, you will see that the waves will reflect. Notice that the reflected waves are at the same angle as the incident waves (this is the name for the waves that are travelling towards the mirror). However, when you use a concave barrier, you will see the waves converge to a point called the focus, while if you use a Convex reflector, the waves will be diverged.

All types of waves can be refracted. Refraction is a change of direction due to a change of speed. For example, water waves travel more slowly in shallow water than in deep water. Light waves can also be refracted when they pass through a glass convex lens. They will converge to the focus.

Diffraction is the name given to the way waves spread out when they pass through a gap. The narrower the gap, the more the waves will spread out. Sea waves passing into a harbour entrance spread out behind the harbour walls.

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