Waves are disturbances which originate from some vibrating source and propagate through a medium and vacuum. A medium is the substance through which a wave can propagate. Water is the medium of water waves. Air is the medium through which we hear sound waves. The electric and magnetic fields are the medium of light. The most important property of wave is it transfer energy from one point to another. Waves transfer energy without transferring the particles of medium.

When a finger is dipped, or a stone is thrown into the water, the water particles are pushed away (disturbed) from their rest position. The surface is now disturbed. It is higher than normal in some places and lower than normal in others. The disturbed water at the point of impact disturbs the water next to it, which in turn disturbs the water next to it, and so on. If you place a cork or anything that floats on water at the middle of the disturbed water it bobs up and down and stays in its position as the ripples pass beneath it. It doesn’t move along with the disturbance. Thus when the disturbance moves forward the particles of the medium vibrate up and down about their mean position of rest but they do not move forward along with the wave.

When the water surface is disturbed only once, we create a pulse through the water. A single non-repeating disturbance traveling in a medium is called a pulse. But when the water is disturbed repeatedly at regular intervals, we create a wave in the water. Thus a pulse is a single disturbance while a wave is a disturbance that is repeated at regular intervals. Examples of common waves that we encounter in our daily life are sound and light. All waves can be characterized by the following characteristics: amplitude, wavelength, period, frequency, and speed.

Key terms

• Pulse: A single disturbance
• Crest: The highest point of a transverse wave.
• Trough: The lowest point of a transverse wave.