<p>These are questions from the 1992 exam-
1. Which of the following would be LEAST likely to result in the separation of white light into spectral colors?
a. Diffraction
b. Dispersion
c. Reflection
d. Interference
e. Refraction</p>
<p>Ans- Reflection</p>
<ol>
<li>Ocean waves moving toward a beach have a speed of 10 metres per second and a frequency of 2 per second.</li>
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<p>The waves are observed by a child sitting in a rowboat offshore. Which of the following properties of the waves seen by the child would be greater when the boat is moving away from the beach than when the boat is stationary with respect to the beach?</p>
<p>I. Speed of the waves with respect to the boat
II. Frequency at which the boat encounters successive wave crests
III. Distance between adjacent wave crests</p>
<p>a. I only
b. III only
c. I and II only
d. II and III only
e. I, II and III </p>
<p>Ans- c</p>
<p>Thanks!</p>
<ol>
<li>Separation of white light into spectral colors is typically done with a prism. It makes use of the fact that different wavelengths have slightly different index of refraction values, so the different colors all “bend” by slightly different amounts and separate into the spectrum. That is why you can eliminate choice E as well as choice B immediately. </li>
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<p>Diffraction is also when you bend a wave; however, there is no chance of medium involved. Diffraction can be used to separate out the spectrum via a diffraction grating so choice A can be eliminated as well.</p>
<p>Interference can be used to cancel out or amplify specific frequencies (colors) and can result in producing a spectrum via thin film interference, so choice D is out.</p>
<p>Reflection just bounces a wave off a surface either specular or diffuse reflection, and although it might result in partial polarization, does not result in dispersion.</p>
<ol>
<li>Essentially this is a variation of doppler effect. When the observer (boat) is moving away from the shore (towards source), you should observe a higher frequency, lower wavelength and higher speed (with respect to observer). When an observer is moving away from the source, it’s the opposite</li>
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