Page 85 - Physics - XII

Table for Refractive index of glass slab

S. Cross-mark without slab Cross-mark with slab Powder sprinkled on the
No. placed on it top of the slab
Main Vernier R = Main Vernier R = Main Vernier R =
2
1
3
Scale Division (a + n Scale Division (b + n Scale Division (c + n
Reading Coinciding × L.C.) Reading Coinciding × L.C.) Reading Coinciding × L.C.)
a n (cm) b n (cm) c n (cm)
(cm) (cm) (cm)

1.
2.

3.

Mean R = _____ cm, Mean R = _____ cm, Mean R = _____ cm
1 2 3
Calculations

Real thickness of the glass slab = R – R = _____ cm
3 1
Apparent thickness of the glass slab = R – R = _____ cm
3 2
Refractive index, µ = Real thickness of slab R 3 R 1
Apparent thickness of slab R R
3 2 2
Result
The refractive index of the material (glass) of the slab is .......... by using travelling microscope.

Precautions

1. The microscope tube should be vertical.
2. Microscope once focussed on the cross-mark, the focussing should not be disturbed throughout the
experiment. Only rack and pinion screw should be used to raise the microscope upward.
3. Eyepiece should be adjusted so that cross-wires are distinctly seen.
4. Only a thin layer of lycopodium powder should be spread on the top of the slab.

5. As far as possible, the rack and pinion screw should be moved in one direction only to avoid
backlash error.
6. Microscope should not be shaky.

Sources of Error

1. Microscope tube may not be vertical.
2. Microscope may be shaky.

EXPERIMENT - 7

Aim
To fi nd the refractive index of a liquid by using convex lens and plane mirror.

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