<text><span class="style10">ave Theory (7 of 11)</span><span class="style7">If a wave travels from one medium to another, the direction of propagation is changed or `bent'; the wave is said to be </span><span class="style26">refracted</span><span class="style7">. The wave will travel in medium 1 with velocity </span><span class="style26">v</span><span class="style7">, and come upon the surface of medium 2 with angle of incidence </span><span class="style26">i</span><span class="style7">. Then the wave will be refracted, as in diagram 10, and </span><span class="style26">r</span><span class="style7"> is the angle of refraction. The new velocity will be </span><span class="style26">v</span><span class="style7">2, which will be less than </span><span class="style26">v</span><span class="style7">1 if medium 2 is more dense than medium 1, but greater than </span><span class="style26">v</span><span class="style7">1 if medium is less dense. The velocities are related by: </span><span class="style26">v</span><span class="style7">1 </span><span class="style26">v</span><span class="style7">2 = sin i sin r and the ratio of sin </span><span class="style26">i</span><span class="style7"> /sin </span><span class="style26">r</span><span class="style7"> is a constant. This constant is the </span><span class="style26">refractive index</span><span class="style7"> of medium 2 with respect to medium 1. This relationship was formulated by the Dutch astronomer Willebrord Snell (1591-1626) and is known as </span><span class="style26">Snell's Law</span><span class="style7">.</span><span class="style10"></span></text>
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<text><span class="style10">0. Refraction of a plane wavefront.</span><span class="style7"> MAN is the normal to XY; </span><span class="style26">i</span><span class="style7"> is the angle of incidence; </span><span class="style26">r</span><span class="style7"> is the angle of refraction. The waves are parallel after refraction.</span></text>
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