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प्रश्न
Describe Fizeau’s method to determine the speed of light.
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उत्तर
Speed of light by Fizeau’s method
Apparatus:
- The light from a source S was first allowed to fall on a partially silvered glass plate G kept at an angle of 45°
- It is then allowed to fall on a rotating tooth wheel with N teeth and N cuts of equal widths.
- Light passing through one cut will be reflected by a mirror M kept at a long distanced (about 8 km)
- If the wheel is not rotating, it gets reflected by a partially silvered glass plate.
Working:
- Angular speed of rotation of wheel was increased from zero to GO Until it blocked by an adjacent tooth.
- It is ensured by the disappearance of light while looking partially silvered glass plate.
Expression:
v = `"2d"/"t"`
where, d = distance, t = time taken
angular speed ω = `theta/"t"`
`theta = (2pi)/(2"N") = pi/"N"`
t = `pi/("N"omega)`
v = `(2"dN"omega)/pi = 2.9972 xx 10^8 "ms"^-1`
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संबंधित प्रश्न
Consider Galileo's method of measuring the speed of light using two lanterns. To get an accuracy of about 10%, the time taken by the experimenter in closing or opening the shutter should be about one tenth of the time taken by the light in going from one experimenter to the other. Assume that it takes 1/100 second for an experimenter to close or open the shutter. How far should the two experimenters be to get a 10% accuracy? What are the difficulties in having this separation?
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(b) with respect to the sun
(c) with respect to a train moving on the earth
(d) with respect to a spaceship going in outer space.
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A ray of light of wavelength 600 nm propagates from air into a medium. If its wavelength in the medium becomes 400 nm, the refractive index of the medium is ______.
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