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.=
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=
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)|
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
|Mean 2A (degree)||A in