# 8. TO USE A TRAVEL CLING MICROSCOPE TO DETERMINE THE REFRACTIVE INDEX OF A GLASS SLAB AND ANALYZE THE VARIATION IN APPARENT DEPtTH WITH REAL DEPTH FOR GLASS PLATES OF DIFFERENT THICKNESSES

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## APPARATUS REQUIRED:

1. Traveling microscope

2. Glass slab of different thickness

3 lycopodium powder.

## THEORY:

The refractive index of the glass slab or liquidis given by:

μ = Real depth / Apparent depth

Let, X₁, X2 and X3 be the reading on the traveling microscope for an object placed on the platform without the glass slab or liquid, with the glass slab or the liquid or with lycopodium powder sprinkled on the glass slab or on the liquid surface respectively Then.

Real depth = X3-X₁

Apparent depth= X3-X2

μ = X3- X ₁ / X3 – X2

For the velocity of light in liquid.

The apparent depth is always smaller than the real depth. When the real depth increases the apparent depth also increases. The graph of real depth d1 against depth d2 is a straight line graph passing through the origin.

## OBSERVATIONS:

20 divisions of main scale = 1 cm

therefore,1 division of main scale = 0.05cm

The number of division on the vernier scale = 90

:. V.C. = Value of 1 main division / No. of division on the vernier scale

= 0.001cm

## RESULT

The refractive index of the glass slab=

PERCENTAGE ERROR

Percentage error in refractive index μ= |S.V. – O. V. /SV | x100%

= 1.556-1.5 / 1.5  X100%

=3.73%

## CONCLUSION:

Hence determine the refractive index of a glass slab of different thickness by using traveling microscope

## PRECAUTIONS:

1. The tobe of the microscope should be exactly vertical.

2. The microscope should be leveled properly.

3. Focus should be sharp once focusing the mark without a glass slab. Object screw shouldn’t be touched throughout the experiment.

4. Very thin layer of lycopodium powder should be sprinkled.