define Michelson method
Answers
Explanation:
Michelson’s Method for Measuring the Speed of Light
In 1931, Albert Michelson devised a method of measuring the speed of light, directly, by finding how long it took to move a measured distance.
The diagram below, showing the approximate arrangement of the apparatus, is not to scale (but I assume you guessed that!)
Light from the source passes through a narrow slit.
It is reflected by face A of the octagonal (8 sided) metal prism.
It then travels a distance of a few kilometres and returns to be reflected by face B.
When the prism is stationary, a stationary image of the slit is observed.
The prism is now rotated.
If the prism rotates fast enough, when light returns to the prism, face B is no longer in the right position to reflect it into the observer’s eye.
The image of the slit disappears.
However, if the speed of rotation is increased, at a certain speed of rotation, the image of the slit reappears.
This is because the time taken for light to go from face A to face B was the same as the time taken by the prism to rotate 1/8th of a revolution.
So, the calculation needed to find the speed of light is remarkably simple:
If the prism completes n rotations per second then
Therefore, the time, t taken for the light to cover the distance, s is 1/8th of this
and so the speed of light c is given by
In 1931, Michelson found c = 2.99774×108ms-1
The modern value is c = 2.997925×108ms-1
Although the calculation is trivially simple don't forget the practical difficulties involved in this experiment: for example, measuring the distance moved by the light to a satisfactory level of precision...
Answer:
Explanation:
✒ Michelson is an American scientists, physicist, and he spent many of the years of his life in measuring the velocity of light. The method devised by him in the year 1926 at the Mount Wilson Observatory is considered accurate.Light is the wave phenomena. It is an electromagnetic wave.
✒ To determine the velocity of light, scientist Michelson established a method and the experimental arrangement of this method is shown in figure below.
✒ The light ray from bright luminous source is passed through a slit S and get reflected from octagonal mirror (having eight faces) O on face 1 so that light reach to the reflecting mirror M1 . From mirror M1, ray reflects to mirror M2. And then it get to reflect from concave mirror C1 of focal length 9 cm and aperture of 60 cm which makes the ray parallel to incident to another concave mirror C2 of same focal length and aperture at distance about 35 km . Now the light reflects to the mirror M3 which is also at focal point of the concave mirror C2 so that it becomes parallel and reach to concave mirror C1 which reflects ray to mirror M4 at focal point . Then light incident to mirror M5. Mirror M5 reflects the light ray to be incident face 5 of the octagonal mirror O .
✒ Here octagonal mirror is rotated in such a way that the light ray covers the total path from face 1 to face 5 of the octagonal mirror . At first the mirror is slowly rotated and then speed is increased so that the clear vision is seen through the telescope refracting from a prism.
✒ Let the mirror rotates n rpm and d be the distance between two concave mirrors. If t be the time period of two successive bright images (At a constant speed image appears clearly at first and becomes faint for a while then after some time it appears clearly hence time period in between these) and C be the velocity of the light, then
✒ By using this we can measure the velocity of light . In Michelson’s method, speed of octagonal mirror was 500 rps and distance was 35 km . He obtain the value of velocity of light in free space C = 2.99775 m/s.