1-16Figure 1-11.—Analogy of refraction.Q14.A refracted wave occurs when a wave passes from one medium into another medium. Whatdetermines the angle of refraction?DiffractionDIFFRACTION is the bending of the wave path when the waves meet an obstruction. The amount ofdiffraction depends on the wavelength of the wave. Higher frequency waves are rarely diffracted in thenormal world that surrounds us. Since light waves are high frequency waves, you will rarely see lightdiffracted. You can, however, observe diffraction in sound waves by listening to music. Suppose you areoutdoors listening to a band. If you step behind a solid obstruction, such as a brick wall, you will hearmostly low notes. This is because the higher notes, having short wave lengths, undergo little or nodiffraction and pass by or over the wall without wrapping around the wall and reaching your ears. Thelow notes, having longer wavelengths, wrap around the wall and reach your ears. This leads to the generalstatement that lower frequency waves tend to diffract more than higher frequency waves. Broadcast band(AM band) radio waves (lower frequency waves) often travel over a mountain to the opposite side fromtheir source because of diffraction, while higher frequency TV and FM signals from the same source tendto be stopped by the mountain.Doppler EffectThe last, but equally important, characteristic of a wave that we will discuss is the Doppler effect.The DOPPLER EFFECT is the apparentchange in frequency or pitch when a sound source moves eithertoward or away from the listener, or when the listener moves either toward or away from the soundsource. This principle, discovered by the Austrian physicist Christian Doppler, applies to all wave motion.The apparent change in frequency between the source of a wave and the receiver of the wave isbecause of relative motion between the source and the receiver. To understand the Doppler effect, firstassume that the frequency of a sound from a source is held constant. The wavelength of the sound willalso remain constant. If both the source and the receiver of the sound remain stationary, the receiver will
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