# To Determine the Dispersive Power of the material of a PRISM

THEORY: –

A spectrometer is use to measure the necessary angle. the spectrometer consists of three unit: 1) collimator, 2) telescope, and 3) prism table, its base and telescope can be independently moved around their common vertical axis. A circular angular scale enables one to red angular displacements (together with two Vernier’s located diametrically opposite to each other).

In the experiment, we need to produce a parallel beam of rays to be incident on the prism. This is done with the help of a collimator. The collimator has an adjustable rectangular slit at one end and a convex lens at the other end. When the illuminated slit is located at the focus of the lens, a parallel beam of rays emerges from the collimator. We can test this point, with the help of a telescope adjusted to receive parallel rays. We first prepare the telescope towards this purpose as follows:

The dispersive power of the material of a prism is given by

where , δmB and δmR are the angles of minimum deviation for Blue and Red colors respectively and A is the angle of the prism .

Therefore ,  Dispersive Power= D.P.=

WHERE,

µB=                              and,    µB=

where , δmB and δmR are the angles of minimum deviation for Blue and Red colours respectively and A is the angle of the prism

Therefore ,  Dispersive Power=

Procedure:

Experimental Results:

1.Determination of Vernier constant of the spectroscope:

2.Table for Determination of minimum   deviation angle;

 Color of light Vernier -1 Vernier -2 Mean δm (degree) MSR VSR TR MSR VSR TR Blue Red Direct Reading

3.Table for Determination of angle of prism :

 No. Of Vernier Reading of telescope on left side(R1) Reading of telescope on right-side(R2) 2A=R1~R2 (degree) Mean 2A  (degree) A  in degree MSR VSR TR MSR VSR TR 1 2

Result:

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