## AIM

To determine the angle of emergence *i'* for varours angle of incidence *i* and to draw the* i-i' *curve.

## APPARATUS

Spectrometer, equilateral prism, sodium light etc.

## THEORY

The graph connecting the angles *i *and *i'* is shown in fig(1). The bisector, meets the curve at P. At the point* P*,* i *and *i' *are equal.

OB = OC = i

The angle of deviation s is given by

* * (1)

Where A is teh angle of the prism.

When* i =i'* , the deviation is minimum (D).

Hence,

(2)

Therefore,

(3)

The regractive index of the prism,

(4)

Therefore,

(5)

Where θ_{2 }is difference between the reflected ray and direct ray.

### Spectrometer i-i' curve

A graph is drawn with angle of incidence i along X-axis and the angle of emergence i' along Y-axis. The graph is a rectangular parabola. from it, angle of incidence corresponding to minimum deviation is calculated.

Fig: 1

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