Ray Optics and Optical Instruments

Refraction and Refractive Index

1. Due to refraction
    1) The stars twinkle
    2) The Sun is seen before the actual Sunrise and still seen after Sunset
    3) Sun appears bigger during Sunset and Sunrise
    4) All the above
Ans: (4)

2. The main cause of decrease in intensity of light on refraction is

       1) Scattering of light

       2) passing of light from one medium to another
       3) total internal reflection
       4) partial reflection and partial absorption
Ans: (2)

      1) only on a      2) only on b     3) only on a, d      4) a, b, c, d
Ans: (4)

4. To travel through same distance in two different media, a light ray of certain frequencey takes different times which are in the ratio 3 : 5, the relative refractive index is
         
Ans: (2)

5. A ray of light passes normally, through a slab (μ = 1.5) of thickness 't'. If the speed of light in vacuum be 'C'. Then the time taken by the ray to go across the slab will be
        
Ans: (3)

6. A ray of light incident on a refracting surface at 30° with the surface. If the angle of refraction is 45°, the refractive index of medium is
       
Ans: (4)

7. If ij represents refractive index when a light ray goes from medium i to medium j. 2µμ₁ × 3μµ₂ × 4μ₃ is equal to
           
Ans: (3)µ

8. Time taken by sunlight to pass through a window of thickness 4 mm with refractive index 1.5 is [speed of light in vacuum = 3 × 10⁸ m/s]  

  1) 2 × 10⁵ s         2) 2 × 10^-11 s         3) 2 × 10^-5 s         4) 2 × 10^-3 s
Ans: (2)

9. Reflected and refracted rays are observed to be perpendicular to each other, when ray of light is incident at an angle of 60° on a transparent block. The refractive index of block is

             
Ans: (3)
 

10. When a ray of light travelling from vacuum to a medium of refractive index μ, the angle of incidence is twice the angle of refraction. The incident angle is

Ans: (2)
 

11. A beam of parallel rays is incident on a transparent slab of refractive index  making an angle 30° with the surface of slab. If the width of incident beam of light is 1.732 mm, the width of refractive beam is
        1) 2.50 mm         2) 3.00 mm         3) 1.50 mm         4) 1.00 mm
Ans: (2)

12. A circular beam of light (diametre = d) falls on a plane surface of a liquid. The angle of incidence is 45° and refractive index of liquid is μ. The diameter or width of refracted beam is

Ans: (1)

Ans: (3)

14. Light ray passes from air into a liquid. The angle of incidence is 60°. The deviation produces is 15°. The refractive index of liquid is
        1) 1.33         2) 1.5       3) 1.22       4) 1.63
Ans: (3)

       1) 1 : 1.1         2) 0.7502 : 1        3) 1 : 1.4         4) 1 : 1.5
Ans: (2)