NUMERICAL PROBLEMS
2. Light passes through a single crystal of ruby 25 m long and emerges with a wavelength of 6.4×10-7 m . If the refractive index of ruby is 1.6, calculate the number of wavelengths inside the crystal. Ans: 6.25×107
3. In Foucault’s method for the velocity of light the distance between the moving and static mirrors was 3 km and the speed of the moving mirror was 500 rev/sec. If the displacement of the returned beam is 7 º12’, find the velocity of light. Ans: 3×108 m/s
4. A beam of light after reflection at a plane mirror rotating 2000 times per minute passes a distant reflector. It returns to a rotating mirror from which it is reflected to make an angle of 1º with the original direction. Assuming that the velocity of light is 3×105 km/s calculate the distance between the mirrors. Ans: 6255m
5. A beam of light is reflected by a rotating mirror onto a fixed mirror, which sends back to the rotating mirror from which it is again reflected and then makes an angle of 3.6º with the original direction. The distance between the two mirrors is 1 km and the rotating mirror is making 750 rev/s. Calculate the speed of light. Ans: 3×108 m/s
6. The radius of curvature of the curved mirror is 20 m and the plane mirror is rotated at 20 rev/s. Calculate the angle in degree between a ray incident on the plane mirror and then reflected from it after the light has travelled to the curved mirror and back to the plane mirror. C = 3×108 m/s. Ans: (1.92×10-3 )º
7. In Foucault’s method the distances of the rotating mirror from the fixed mirror and the lens were 20 m and 6 m respectively. The source of light was placed at a distance of 210 cm from the lens. When the plane mirror was rotated at the rate of 258 rev/sec, the shift of the image was recorded to be 0.7 mm. Calculate the speed of light. Ans: 3×108 m/s
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