This explains how we can hear the words of someone who is facing away from us. It is the principle of refraction that makes the lenses in spectacles work.ĭiffraction occurs when waves passing through a slit which is narrow compared to the wavelength are spread out and depart from the expected straight line direction. An example is when light enters a lens or prism – the light is bent. Refraction Refraction is the change of direction of a wavefront as it passes obliquely (at any angle which is not perpendicular or parallel) from one medium to another in which its speed is altered. Important example of a wave reflection is an echo, when sound waves bounce off a faraway surface. Reflection is the process whereby part or all of a wave is returned when it encounters the boundary between two different materials or media. PROPERTIES OF WAVES Waves have several properties, including reflection, refraction, diffraction and interference. The speed of a sound wave in air at 20☌ (68☏) is 344 m/s, but in water sound travels at 1461 m/s and in steel its speed is 5000 m/s. Audible sound frequencies range from 20 Hz (a low rumble) to about 20,000 Hz (a shrill whistle). The frequency (f) of a wave is defined as the number of complete oscillations per second. WAVE LENGTH AND FREQUENCY The distance between successive wave crests is called the wavelength, X (lamda). In transverse waves the vibrations are perpendicular to the direction of travel, whereas in longitudinal waves the vibra tions are parallel to the direction of travel. There are two main types of waves: transverse and longitudinal. Examples of waves include water waves, sound waves, light and X-rays. X-rays, ultraviolet rays, light and radio waves all travel at the same speed through a vacuum. A wave is a phenomenon whereby energy is moved without the transference of any material.
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