# 5. TO VERIFY THE LAWS OF REFRACTION OF LIGHT BY USING A GLASS SLAB.

## APPARATUS REQUIRED

1. Glass slab

2. A sheet of white paper

3. Drawing board

4. Scale, protractor, pencil, pins

5. Compass

## THEORY

Refraction: The phenomenon of bending of light when it travels from one medium to another medium is known as refraction.

### Snell’s law:

According to this law the ratio of the sine of the angle of incidence (i) to sine of the angle of refraction (r) is always constant This constant ratio is called refractive index (u).

i.e.

μ₁ = Sin (1) / Sin (r)

If Pa and Pg are the length of the perpendicular in air and in glass, then refractive idea is given by

H₂ = Sin(i) / Sin(r)   = Pa/hypotenuse / Pg/hypotenuse

therefore, H₂ = Pa/Pg

## ORSERVATION:

Least count of scale = 0.1cm

least count of protector = 1°

Table 1: (Using protector)

Table 2: (without using protector)

## CALCULATION

Refractive index of the glass slab

1) Using a protector, H₁ = 1.65

2) Without using a protector, H₂ = 1.82

## RESULT

The refractive index of glass slab: H1+ H₂ / 2

= 1.65+1.82 / 2

= 1.735

## PERCENTAGE ERROR

Percentage error in refractive index of glass slab is

= |standard value – observed value / standard valve|x 100%

=|1.5-1.735 / 1.5| x100%

=15.67%

## PRECAUTION

1. The pins should be exactly radical

2. The distance between two pins should be about 40cm. Retracted images are observed 30 cm from the glass slab.

3. Angles should be measured with?

## OBSERVATION:

Least count of scale = 0.1cm

least count of protector=

Table 1: (Using a protector)

Table: 2 (without using protactor)

Perpendicular on

## CALCULATIONS:

Refractive index of the glass slab

i) Using a protactor, (μ) = 1.4998

ii) Without using a protactor, (μ) = 1.4364

## RESULT:

The mean refractive index of glass slab is found to be 1.4681.

## PERCENTAGE ERROR:

Percentage error in refractive index of glass slab is

=|Standard valve – observed value / Standard valve| x 100%

=|1.5-1.4681/ 1.5| x 100%

= 2.12%

## CONCLUSION:

Hence, the laws of refraction were verified and determined the refractive index of a glass slab.