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Class 12  »  Physics  »  Ray Optics and Optical Instruments

Refraction Laws and Refractive Index - UNSOLVED PRACTICE SET

Class 12

Chapter: Ray Optics and Optical Instruments | Topic: Refraction Laws and Refractive Index

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Class 12

REFRACTION LAWS AND REFRACTIVE INDEX - UNSOLVED PRACTICE SET

Topic: Refraction Laws and Refractive Index

Time: 40 mins | Marks: 30 | Difficulty: Medium

Multiple Choice Questions

Q1. The first law of refraction states that:

  1. The incident ray, refracted ray, and normal all lie in different planes
  2. The incident ray, refracted ray, and normal all lie in the same plane
  3. The angle of incidence equals the angle of refraction
  4. Light bends away from the normal when going from rarer to denser medium

Q2. Snell's law of refraction is:

  1. n₁ sin i = n₂ sin r
  2. n₁ sin r = n₂ sin i
  3. sin i = sin r
  4. n₁ + n₂ = sin i + sin r

Q3. When light travels from a denser medium to a rarer medium, it bends:

  1. Towards the normal
  2. Away from the normal
  3. Does not bend at all
  4. Perpendicular to the normal

Q4. The refractive index of a medium with respect to vacuum is called:

  1. Relative refractive index
  2. Absolute refractive index
  3. Specific refractive index
  4. Critical refractive index

Q5. The speed of light in a medium of refractive index n is:

  1. c × n
  2. c / n
  3. c + n
  4. c − n

Q6. If the refractive index of glass with respect to water is 9/8 and that of water with respect to air is 4/3, the refractive index of glass with respect to air is:

  1. 3/2
  2. 2/3
  3. 32/27
  4. 27/32

Short Answer Questions

Q7. State the two laws of refraction of light. Illustrate with a labeled diagram.

Q8. Define refractive index of a medium. How is it related to the speed of light in that medium?

Q9. Why does a stick partially immersed in water appear bent at the water surface? Explain with a ray diagram.

Q10. Light travels from air (n = 1) to glass (n = 1.5). If the angle of incidence is 30°, calculate the angle of refraction.

Q11. What is the physical significance of refractive index? Why does light slow down in an optically denser medium?

Q12. The refractive index of diamond is 2.42. What does this tell you about the speed of light in diamond compared to air?

Long Answer Questions

Q13. State and prove Snell's law of refraction using Huygens' wave theory. Explain the physical basis of refraction.

Q14. Derive the relationship between refractive index and the speed of light in a medium. Show that the refractive index of medium 2 with respect to medium 1 is equal to the ratio of the speed of light in medium 1 to the speed of light in medium 2.

Q15. Explain the phenomenon of apparent depth with the help of a ray diagram. Derive the expression for apparent depth in terms of real depth and refractive index.

Numerical & Application-Based Problems

Q16. Light enters from air into a glass slab of thickness 10 cm and refractive index 1.5 at an angle of incidence of 45°.

(a) Calculate the angle of refraction in glass.

(b) Calculate the speed of light in glass.

(c) Calculate the lateral displacement of the emergent ray.

(d) Verify that the emergent ray is parallel to the incident ray.

Q17. A coin is placed at the bottom of a beaker containing water (refractive index 4/3) to a depth of 12 cm.

(a) Calculate the apparent depth of the coin as seen from above.

(b) Calculate the refractive index of water with respect to glass if the refractive index of glass is 1.5.

(c) If the beaker is viewed from an angle of 30° from the vertical, will the apparent depth be the same? Explain.

Q18. In your school's physics lab, a student performs an experiment to determine the refractive index of a glass slab using a travelling microscope.

(a) She measures the real thickness of the slab as 15.0 mm. When viewed through the microscope, the apparent thickness is 10.0 mm. Calculate the refractive index of the glass.

(b) The student then repeats the experiment with a liquid in a glass container. The real depth of the liquid is 20.0 cm and the apparent depth is 15.0 cm. Calculate the refractive index of the liquid.

(c) A classmate suggests that the refractive index of the liquid with respect to glass can be found by simply dividing the two refractive indices calculated above. Verify this mathematically.

(d) Explain why a diamond sparkles more than a glass piece of the same shape, using the concept of refractive index.


Total: 30 Marks | Time: 40 mins

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