Principle- In Michelson interferometer a beam of light from an extended source is divided into two parts of equal intensities by partial reflection & refraction.These beams travel in two mutually perpendicular directions & come together.After reflection from plane mirrors the beams overlape to each-other & produce interference fringes. Construction- It consists of a beam spliter G1 ,a compensating glass G2 and two plane mirrors M1 and M2.The beam spliter G1 is a partially silvered plane parallel glass plate.The compensating plate G2 is a simple plane parallel glass plate having the same thickness as G1.The two plates G1 and G2 are held parallelto each-other and are inclined at an angle of 45 with respect to mirror M2.The mirror M1 is mounted on a carriage and can be moved exactly parallel to itself with the help of a micrometer screw.The distance through which the mirror M1 is moved can be read with the help of a graduated drum attached to the screw.The interference bands are observerd in the field of view of the telescope. Working- Monochromatic light from an extended source S is rendered parallel by means of a colliminating lense & is made incident on the beam spliter G1.It is partly reflected at the back surface of G1 along AC and partly transmitted along AB.The beam AC travels normally towards the plane mirror M1 and is reflected back along AT. The transmitted beam travels towards the mirror M2 and is reflected along the same path.It is reflected at the back surface of G1 and proceeds along AT. The two beams received along AC are produced from a single source through division of amplitudes & are coherent.The superposition of these beams leads to interference and produced interference fringes.
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