Questions-Refraction of Light At Plane Surfaces Questions

Refraction of Light At Plane Surfaces

1/2 Mark Questions

 1. Write Snell’s law.

Ans: n1 sin i = n2 sin r or 

n1/n2 = sin r / sin i

2. What is the Speed of light in vacuum ?

Ans: 3 ×10 power 8 m/s

3. What is the reason behind the twinkling of stars ? (OR)

 Suggest reasons for the phenomenon associated with the following: Twinkling of stars.

Ans: Refraction of light

4. The refractive index of a transparent material is 3/2. Then what is the speed of the light in that medium ?

Ans: 2 ×10 power 8 m/s

5. Why a lemon kept in a glass of water appears to be bigger than its actual size ?

Ans: Due to refraction of light.

6. Can you guess what happen when light ray travels from a denser medium to a rarer medium?

Ans: When the light ray travels from denser to rarer medium, it bends away from the normal.

7. What happen when light ray travels from a rarer medium to a denser medium ?

Ans: When light ray travels from a rarer medium to a denser medium, the refracted ray bends towards the normal.

8. Why a coin kept at the bottom of a vessel filled with water appears to be raised ?

Ans: Due to refraction of light.

9. What is the reason when a thick glass slab is placed over some printed letters, the letters appear raised when viewed through the glass slab ?

Ans: Refraction of light

10. Relative refractive index n21 = ..................

 A) n1/n2 B) n2/n1 C) n12 /n21 D) C/V

1 Mark Questions

1. What is the speed of light in vacuum?

Ans: The Speed of light in vacuum is = 3 × 10power of 8 m/s.

2. Define “Refraction of Light”.

 Ans: The process of changing speed at an interface when light travels from one medium to another resulting in a change in direction is called refraction of light. 

3. Define “Refractive index” or “Absolute Refractive index”.

 Ans: The ratio of speed of light in vacuum to the speed of light in a medium is defined as refractive index (n). It is also called as absolute refractive index.

4. Define snell's law.

 Ans: when light travels from one medium to another, the ratio of n1 sin i = n2 sin r. This is called Snell’s law.

5. Is there any chance that angle of refraction is equal to 90o ? When does this happen ?

 Ans:Yes. When the angle of incidence is equal to the Critical angle, then the angle of refraction is equal to 90o.

6. Define relative refractive index.

Ans: Relative refractive index: The refractive index of a medium with respect to another medium is defined as the ratio of speed of light in the first medium to the speed of light in the second medium.

7. In which case the angle of incidence is equal to the angle of refraction ?

 Ans: When the refractive indices of two media are equal, then the angle of incidence is equal to the angle of refraction.

8. What happens to light when the angle of incidence is greater than critical angle?

Ans: When the angle of the incidence is greater than critical angle, the light ray gets reflected into the denser medium at the interface. This phenomenon is called “total internal reflection”.

9. Why do stars appear twinkling ?

 Ans: 1. The light from stars travels through different layers of air to reach our eye.

2. These air layers have different optical densities and they offer different refractive index values.

3. Due to this the light bends many times.

4. When this retracted light reach our eye, we see stars as twinkling.

10. When we sit at a campfire, objects beyond the fire are seen swaying. Give the reason for it.

 Ans:1. Due to refraction of light, the objects beyond the fire are seen swaying When we sit at a campfire.

2. The light from the objects beyond the fire is get refraction before reaching our eye.

3. The density of surrounding air also changes due to the heat of campfire.

4. That's why the objects beyond the fire are seen swaying.

11. On what factors does the refractive index of a medium depend ?

 Ans: Refractive index of the material depends on the following factors.

 1. Nature of the material.

 2. Wavelength of light used.

12. Write the laws of refraction.

 Ans: laws of refraction:

 1. The incident ray, the refracted ray and the normal all lie in the same plane.

 2. During the refraction light follows Snell’s law.

 n1 sin i = n2 sin r

13. How do you appreciate the role of Fermat principle in drawing ray diagrams.

Ans: 1. Fermat’s principle says that light selects a shortest path to travel.

2. This is the basic reason for the straight line propagation of light.

3. Using this principle, we can draw ray diagram to trace the image formed by mirrors to understand reflection and refraction.