Practical No. 14: Determination of the refractive index of glass slab.

 Practical No. 14: Determination of the refractive index of glass slab.

• The refractive index of glass calculated using the formula μ = 1/sin C was found to be approximately 1.5, which is a standard value for common glass. This confirms the phenomenon of total internal reflection.

• It is concluded that the refractive index of a material can be determined accurately by measuring its critical angle.
• It is recommended to use a very sharp pin and mark points carefully for an accurate measurement of the critical angle.

• Answer: Snell’s law states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media and for light of a given colour. This constant is called the refractive index.
  • Formula: n1 sin i = n2 sin r

• Answer: The critical angle is the angle of incidence in the denser medium for which the angle of refraction in the rarer medium is 90 degrees.

• Answer: The two conditions for Total Internal Reflection (TIR) are:
  1. Light must travel from a denser medium to a rarer medium.
  2. The angle of incidence in the denser medium must be greater than the critical angle for that pair of media.

• Answer:
  • Given Data: Angle of incidence (i) = 35°, Angle of refraction (r) = 40°
  • Calculation: (Assuming light is entering from air where n1 ≈ 1)
    • Snell’s Law: n1 sin i = n2 sin r
    • 1 × sin(35°) = n2 × sin(40°)
    • n2 = sin(35°) / sin(40°)
    • n2 = 0.5736 / 0.6428
    • n2 ≈ 0.892
      (Note: This value is less than 1, which suggests the second medium is rarer than air, which is unusual but possible, e.g., light entering air from water. The question should specify the media).

• Answer: (b) Variation of refractive index in the atmosphere
  • Explanation: The twinkling is caused by atmospheric refraction. Starlight bends through layers of air with varying densities and refractive indices, causing the apparent position of the star to fluctuate.