CBSE Class 12 Physics Ray Optics Optical Instruments Worksheet Set E

CBSE Class 12 Physics Ray Optics Optical Instruments Important Questions (3). Students can download these worksheets and practice them. This will help them to get better marks in examinations. Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

1. Define Magnification of a lens. Compare the magnification of a convex lens with that of a concave lens. 

2. A magician during a show makes a glass lens with n= 1.47 disappear in a trough of liquid. What will be the nature of the lens inside the liquid? What is the refractive index of the liquid? Could the liquid be water? 

3. Define power of a lens. What is the physical significance of it? Give the formula for finding the power of a lens and the SI unit of measurement of it. 

4. A converging lens of refractive index 1.5 is kept in a liquid medium having same refractive index. What would be the focal length of the lens in this medium? (Hint: Refraction of light depends upon the passage of light from one medium to another)

5. If f= 0.5m for a glass lens, what is the power of the lens? (ii) The radii of curvature of the faces of a double convex lens are 10cm and 15 cm. Its focal length is 12cm. What is the refractive index of glass? (iii) A convex lens has 20 cm focal length in air. What is the focal length in water? (Refractive index of air-water=1.33. refractive index of air-glass=1.  

Important Questions for NCERT Class 12 Physics Ray Optics and Optical Instruments

Question. A green light is incident from the water to the air - water interface at the critical angle (q). Select the correct statement.    

(a) The entire spectrum of visible light will come out of the water at an angle of 90º to the normal.
(b) The spectrum of visible light whose frequency is less than that of green light will come out to the air medium.
(c) The spectrum of visible light whose frequency is more than that of green light will come out to the air medium.
(d) The entire spectrum of visible light will come out of the water at various angles to the normal.

Answer :   B

Question. An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be
(a) 30 cm away from the mirror
(b) 36 cm away from the mirror
(c) 30 cm towards the mirror
(d) 36 cm towards the mirror. 

Answer :   B

Question. A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle q, the spot of the light is found to move through a distance y on the scale. The angle q is given by
(a) y/x
(b) x/2y
(c) x/y
(d) y/2x

Answer :   D

Question. Two plane mirrors are inclined at 70°. A ray incident on one mirror at angle, q after reflection falls on second mirror and is reflected from there parallel to first mirror. The value of q is
(a) 45°
(b) 30°
(c) 55°
(d) 50°

Answer :   D

Question. A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is
(a) 10 cm
(b) 15 cm
(c) 2.5 cm
(d) 5 cm. 

Answer :   D

Question. A tall man of height 6 feet, want to see his full image. Then required minimum length of the mirror will be
(a) 12 feet
(b) 3 feet
(c) 6 feet
(d) any length

Answer :   B

Question. A beam of light composed of red and green ray is incident obliquely at a point on the face of rectangular glass slab. When coming out on the opposite parallel face, the red and green ray emerge from
(a) two points propagating in two different non parallel directions
(b) two points propagating in two different parallel directions
(c) one point propagating in two different directions
(d) one point propagating in the same directions.

Answer :   B

Question. A ray of light travelling in air have wavelength l, frequency n, velocity v and intensity I. If this ray enters into water then these parameters are l′, n′, v′ and I′ respectively. Which relation is correct from following?
(a) l = l′
(b) n = n′
(c) v = v′
(d) I = I′ 

Answer :   B

Question. A bubble in glass slab (m = 1.5) when viewed from one side appears at 5 cm and 2 cm from other side, then thickness of slab is
(a) 3.75 cm
(b) 3 cm
(c) 10.5 cm
(d) 2.5 cm 
9.4 Total Internal Reflection

Answer :   C

Question. A ray of light travelling in a transparent medium of refractive index m, falls on a surface separating the medium from air at an angle of incidence of 45°.
For which of the following value of m the ray can undergo total internal reflection?
(a) m = 1.33
(b) m = 1.40
(c) m = 1.50
(d) m = 1.25

Answer :   C

Question. If a convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together, what will be their resulting power?   
(a) + 7.5 D
(b) –0.75 D
(c) + 6.5 D
(d) –6.5 D 

Answer   B

Question. Focal length of a convex lens of refractive index 1.5 is 2 cm. Focal length of lens when immersed in a liquid of refractive index of 1.25 will be    
(a) 10 cm
(b) 2.5 cm
(c) 5 cm
(d) 7.5 cm

Answer   C

Question. If fV and fR are the focal lengths of a convex lens for violet and red light respectively and FV and FR are the focal lengths of a concave lens for violet and red light respectively, then we must have    
(a) fV > fR and FV > FR
(b) fV < fR and FV > FR
(c) fV > fR and FV < FR
(d) fV < fR and FV < FR

Answer   B

Please click the link below to download CBSE Class 12 Physics Ray Optics Optical Instruments Important Questions (3).