Question

a-) Explain in detail the reason why the center is dark in the enlightenment setup in the Newton rings experiment.

b-) You want to determine the absorption coefficient. Draw the experimental setup and explain why you use the elements.

c- ) You want to observe that light can be polarized. Draw the experimental setup and explain why you use the elements.

Answer 1

A) in the Newtons rings experiment , at the centre the thickness of the film of air formed between glass plate and lens is zero. Hence at the centre the geometrical path difference between the incident ray and the reflected ray from the glass plate becomes zero. But as the reflection occurs path difference of   get introduced . This path difference gives destructive interference at the centre. Hence centre is dark in the enlightenment setup in the Newtons rings experiment .

B) experimental setup to determine absorption coefficient of light :

In the experimental setup for determination of absorption coefficient , hydrogen or tungsten discharge lamp is used as the light source. The light is then passed through the monochromater through which light of single wavelength is only get passed. This light of single wavelength is then passed through the reference cell. Which then detected using photodetector and passed to the spectrophotometer. It measures the intensity of light. The intensity of light (I_o) then observed is considered as the reference for the later experiment.  

After this same light of that single wavelength is passed through a cuvette consisting of light absorbing sample solution of concentration (c) and of thickness () . The light then passed is detected by photodetector and it's intensity (I) is given by the spectrophotometer.  

The absorption is given by the beer Lambert law which is,

A = log( I / I_o ) = c.

Where epsilon () = absorption coefficient of light.  

c = concentration of sample.

= length of light path = thickness of cuvette.  

Here,  

Absorbance is directly proportional to the length Of light path I. E. Thickness of cuvette and concentration of light absorbing sample.

C) experimental setup for polarization of light phenomenon :

Polarization of light is the phenomenon in which particular vibrations of the light restricted on the given fixed plane.

For observation of polarization phenomenon of light tourmaline crystals are used as the polarizer and analyzer . For this ordinary light which is unpolarized , is passed through the polarizer . it get plane polarized.  

If the analyser is rotated such that the optical axis of polarizer is parallel to the optical axis of analyser , we get maximum intensity light as output, whereas intensity starts to minimum as their axes gets perpendicular to each other.