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
| No.of obs. | Glass slab with different thickness | Reading on the microscope when it’s focused on cross mark Without with the with the Glass glass lycopodiumSlab slab powder | Real depth =X3-X1 cm | Apparent depth =X3-X2 | μ= X3-X1/X3-X2 | Meanμ |
| 1 | M.S V.S total M.S V.S total M.S V.S total | |||||
| 2 | 1st slab | 4.2 4.1 4.24 4.9 32 4.932 6.2 | 1.27 | 1.27 | 1.54 | |
| 3 | ||||||
| 1 | ||||||
| 2 | 2nd slab | 4.1 1.5 4.45 4.8 39 4.83 6.1 40 6.14 | 1.301 | 1.301 | 1.56 | 1.56 |
| 3 | ||||||
| 1 | ||||||
| 2 | 3rd slab | 6.6 11 6.611 7.2 81 7.2 8.4 41 8.4 | 1.16 | 1.16 | 1.57 | |
| 3 |
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.