Class 12 Physics Lab Experiments

To determine the refractive index of a glass using travelling microscope

May 28 2023

Aim

To determine the refractive index of a glass using travelling microscope.

A marker, glass slab, travelling microscope, lycopodium powder.

The refractive index, μ= real depth /apparent depth = r₃-r ₁/r ₂-r ₁

Least count of travelling microscope = 0.001 cm or 0.01 mm Mean values: r₁ = 0 mm r ₂ = 6.81 mm r ₃= 10.25 mm

S.No.	Mark without slab r₁= M + n x LC min	Mark with slab on it r₂= M + n x LC min	Powder on top of slab r₃= M + n x LC min
1	0	6.5 + 29 x 0.01 = 6.79mm	10 + 23 x 0.01 = 10.23mm
2	0	6.5 + 31 x 0.01 = 6.81mm	10 + 25 x 0.01 = 10.25mm
3	0	6.5 + 33 x 0.01 = 6.83mm	10 + 27 x 0.01 = 10.27mm

Real depth = d_r = r ₃ – r ₁ = Mean d _r= 10.25 mm

Apparent depth = d _a= r ₂ – r ₁1

Mean d_a= 6.81 mm

∴ Refractive index, μ = real depth /apparent depth = d_r/d_a ∴μ= 1.52

The refractive index of the glass slab by using travelling microscope is determined as 1.52=μ

Microscope once focused on the cross mark, the focusing should not be disturbed throughout the experiment. Only rack and pinion screw should be turned to move the microscope upward.
Only a thin layer of powder should be spread on top of slab.
Eye piece should be so adjusted that cross-wires are distinctly seen.