Michelson interferometer is a widely used instrument for measuring wavelength of light, refractive index of transparent materials etc. The interferometer (Model No. HO-ED-INT-06) is designed and constructed in modular fashion. The beam splitter is designed to reflect 50% of the incident light and transmit the other 50%. The incident beam therefore is split into two beams; one beam is reflected towards mirror M1, the other is transmitted towards mirror M2. Half the light is transmitted through the beam splitter to M1 and the other half is reflected by beam splitter to M2. The reflected beams from M1 and M2 superimpose at the beam splitter and the interference pattern can be observed on the screen.
The wavelength of laser is calculated by ;
λ = (2d / N) Δ
where 'd’ is the change in position that occurs for ‘N’ fringes to pass and Δ is the calibration constant of the micrometer
The light passes through a greater length of glass as the plate is rotated. The change in the path length of the light beam as the glass plate is rotated and relates the change in path length with the laser beam through air.
The refractive index of glass slide,
N = (2t - Nλ) (1 - cos θ) / 2t (1 - cos θ) - Nλ
Where t is the thickness of the glass slide, N is the number of fringes counted, λ is the wave length of light used and θ is the angle turned for N fringes.
Let λ be the wavelength of light, n the refractive index of air at atmospheric pressure, d the length of the air cell, Patm the current atmospheric pressure and ΔP the pressure change. The relationship between the pressure change ΔP and the number of fringe shift mΔP is given by,
mΔP = (2d (n-1) / λ) (ΔP / Patm)