LIGHT, Class X, MCQ Part -4

 

                                 MCQ'S

MCQ Questions for Class 10 Science Light Reflection and Refraction with Answers.                    

Students can solve NCERT Class 10 Science Light Reflection and Refraction (part-2) Latest Exam Pattern Multiple Choice Questions with Answers to know their preparation level.

Question1. The refractive index of medium A is 1.5 and that of medium B is 1.33. If the speed of light in air is 3 × 108 m/s. What is the speed of light in medium A and B respectively?
(a) 2 × 108 m/s and 1.33 × 108 m/s. 
(b) 1.33 × 108 m/s and 2 × 108 m/s. 
(c) 2.25 × 108 m/s and 2 × 108 m/s. 
(d) 2 × 108 m/s and 2.25 × 108 m/s. 

Answer. (d) 2 × 108 m/s and 2.25 × 108 m/s. 
(Here c = 3 × 108 m/s

Question 2. An object of height 4 cm is kept at a distance of 30 cm from the pole of a diverging mirror. If the focal length of the mirror is 10 cm, the height of the image formed is:
(a) + 3.0 cm
(b) + 2.5 cm
(c) + 1.0 cm
(d) + 0.75 cm

Answer.(c) + 1.0 cm 

( Here u = - 30 cm, f = + 10 cm and h = + 4 cm.


Question3. Which of the following mirrors is used by a dentist to examine small cavities in a patient’s teeth?                                                                       .(a) Convex mirror                                                                                                   (b) Plane mirror                                                                                                      .(c) Concave mirror                                                                                                      (d) Any spherical mirror

Answer. (c) Concave mirror
(A dentist uses a concave mirror of small focal length to form a magnified and erect image of a tooth being examined by him)

Question4. Which of the following can make a parallel beam of light when light from a point source is incident on it?
(a) Concave mirror as well as convex lens.
(b) Convex mirror as well as concave lens.
(c) Two plane mirrors placed at 900 of each other.
(d) Concave mirror as well as concave lens.

Answer. (a) Concave mirror as well as convex lens.

(When light from a point source situated at the focus point of a concave mirror or a convex lens is incident on the mirror/lens, we get a parallel beam of light after reflection/refraction)

Question5. Two convex lenses P and Q have focal lengths of 0.50 m and 0.40 m respectively. Which of the following is true about the combined power of the two lenses?
(a) P is equal to 4.5 D.
(b) P is less than 4.5 D.
(c) P is more than 4.5 D.
(d) P cannot be determined from the information given.

Answer. (a) P is equal to 4.5 D.
(Combined power P is equal to 4.5 D. 
Here P1= 1/0.50 = +2.0 D and P2= 1/0.40 = +2.5 D.
Combined power, P = P1  + P2  = 2.0+2.5= + 4.5 D)

Question6. Rays from Sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that the size of its image is equal to the size of the object?

(a) 30 cm in front of the mirror.                                                                             

(b) 15 cm in front of the mirror. 

(c) Between 15 cm and 30 cm in front of the mirror.

(d) More than 30 cm in front of the mirror.

Answer.  (a) 30 cm in front of the mirror. 
( When the object is situated at centre of curvature of a concave mirror, i.e., u = 2f. The real and inverted image of the same size is formed at the centre of curvature itself) 

Question7. If the real image of a candle flame by a lens is three times the size of the distance between lens and lens and the image is 80 cm, at what distance should the candle be placed from the lens?

(a) - 80 cm.

(b) - 40 cm.

(c) - 40/3 cm.

(d) - 80/3 cm.

Answer. (d) - 80/3 cm.

( Here h' = - 3h and v = 80 cm 

 

Question8. The refractive index of flint glass is 1.65 and that of alcohol is 1.36 with respect to air. What is the refractive index of the flint glass with respect to alcohol?
(a) 0.82
(b) 1.21
(c) 1.11
(d) 1.01
Answer. (b) 1.21

                                                                                                           

Question9. When an object is kept within the focus of a concave mirror, an enlarged image is formed behind the mirror. This image is

(a) real. 
(b) inverted.
(c) virtual and inverted.
(d) virtual and erect.

Answer. (d) virtual and erect.

( When an object is kept within the focus of a concave mirror i.e., a virtual and enlarged image of the object is formed)

Question10. A Concave mirror is used to form an image of the sun on a white screen. If the lower half of the mirror is covered with black paper, the erect image formed on the screen would be

(a) to make the image less bright than before.

(b) to make the lower half of the image disappear.

(c) to prevent the image from being focused.

(d) to make the image smaller in size.

Answer. (a) to make the image less bright than before.

( If the lower half of a mirror is covered with black paper, a complete image of the object will be formed. However, the brightness of the image will be less now)

Question11. When an incident ray of light enters a medium from air, it bends towards the normal. Which of the following is true about the refractive index of the medium (nm) as compared to the refractive index of air (na)?
(a) nm is equal to na.                                                                                            (b) nm is less than na.                                                                                          (c) nm is more than na.                                                                                       (d) Then refractive index cannot be compared based on the given information.

Answer. (b) nm is less than na.

Question12. Ray from the sun converges at a point 15 cm in front of a concave mirror. Where should an object be placed so that the size of the image is exactly equal to the size of the object?
(a) 30 cm in front of the mirror.                                                                               (b) 15 cm in front of the mirror.                                                                           (c) Between 15 cm and 30 cm in front of the mirror.                                           (d) Less than 15 cm in front of the mirror.

Answer.(a) 30 cm in front of mirror.                                                                         ( As sunlight 'u= infinity' converges at a point 15 cm in front of the given mirror, f= - 15 cm. To form an image of exactly equal size to the object, it must be placed at the center of the curvature of the mirror. It  means that now, u= R = 2f = 30 cm) 

Question13. A virtual, erect, and magnified image of an object is to be produced with a concave mirror of focal length 12 cm. Object may be placed at a distance of,
(a) 10 cm from the mirror.                                                                                   (b) 15 cm from the mirror.                                                                                (c) 24 cm from the mirror.                                                                                 (d) 48 cm from the mirror.

Answer. (a) 10 cm from the mirror.                                                                        ( A concave mirror forms a virtual, erect, and magnified image when an object is placed between the poles and focus point of the mirror. As the focal length of the given concave mirror, hence object must be placed at a distance less than 12cm i.e., u< 12 cm. Thus, the object may be placed at a distance of 10 cm from the mirror)

Question14. An object is placed at a distance of 40 cm from a convex lens and its real and inverted image of the same size is formed on a screen placed on the other side of the lens. The focal length of the lens is
(a) + 40 cm
(b) + 20 cm
(c) - 20 cm
(d) + 80 cm

Answer. (b) + 20 cm 

(As u= - 40 cm and v = + 40 cm, 

hence 1/f = 1/v -1/u = 1/ - 30 + 1/ - 60 = - 1/ 20 
f = + 20 cm)
 
Question15. A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is,
(a) - 30 cm
(b) - 20 cm
(c) - 40 cm
(d) - 60 cm

Answer. (b) - 20 cm 

(As h = 10 m, h' = 5 mm and v = - 30 cm,

 .     

Question16. Which of the following statements is true?
(a) A convex lens has + 4 D power having a focal length + 0.25 m.
(b) A convex lens has - 4 D power having a focal length + 0.25 m.
(c) A concave lens has + 4 D power having a focal length + 0.25 m.
(d) A concave lens has - 4 D power having a focal length + 0.25 m.

Answer. (a) A convex lens has + 4 D power having a focal length of + 0.25 m.

( If the focal length of a convex lens f = + 0.25 m, then its power p = 1/f  
p =1/f = + 1/0.25 m= 4 D)

Question17. The focal length of a plane mirror is,
(a) 0.
(b) infinity. 
(c) it does not have a focal length. 
(d) None of these. 

Answer. (b) infinity.

( For a plane mirror v = - u and so 1/f = 1/ - v + 1/u = 0 = infinity )

Question18. A girl is standing in front of a magic mirror. She finds the image of her head bigger, the middle position of her body of the same size, and that of the legs smaller. The order of the combination for the magic mirror from the top is
(a) Convex, Plane and Concave.
(b) Plane, Convex, and Concave.
(c) Concave, Plane and Convex.
(d) Convex, Concave and Plane.

Answer. (c) Concave, Plane, and Convex.

(Concave mirror forms a magnified image of the head, Plane mirror forms an image of the middle portion of the body having the same size, and convex mirror forms a diminished image of legs)

Question19. A Convex lens of power 4 D is brought in contact with a Concave lens of power - 2 D. The power of lenses in combination is, 
(a) + 6 D 
(b) + 2 D
(c) - 2 D
(d) - 6 D

Answer.(b) + 2 D

(Power, P = P = P1 + P2 = + 4 + ( - 2) = + 2 D

Question20. A converging lens forms a three-times magnified image of an object, which can be taken on a screen. If the focal length of the lens is 30 cm, then the distance of the object from the lens is:
(a) - 55 cm.
(b) - 50 cm.
(c) - 45 cm.
(d) - 40 cm.

Answer. ( d ) - 40 cm.

( As per question f = + 30 cm and m = - 3 
 v/u = - 3 or v = - 3u
as 1/f = 1/v + 1/u 
hence 1/+30 = 1/-3u -1/u = - 4 / 3u
u = = - 40 cm)



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