Extra Important Questions

Salwan Girls Senior Secondary School 4265 to 4267 gali no. 61 Reghar Pura Karol Bagh Ne CLASS 10 - SCIENCE Maximum Marks: 81 Light Solutions Time Allowed: 4 hours Section A 1. A full length image of a distant tall building can definitely be seen by using a) both concave as well as plane mirror b) a plane mirror c) a concave mirror d) a convex mirror 2. For an incident angle i refraction angle was found to be r1 and r2 (r2 > r1) for two medium A and B respectively. Then a) A is denser than B b) We cannot identify the denser medium c) Both are equally dense d) B is denser than A 3. A beam of light is incident through the holes on side A and emerges out of the holes on the other face of the box as shown in the Figure. Which of the following could be inside the box? a) Prism b) Concave lens c) Convex lens d) Rectangular glass slab 4. The laws of reflection hold good for a) convex mirror only b) concave mirror only c) plane mirror only d) all mirrors irrespective of their shape 5. Four students reported the following observation tables for the experiment, to trace the path of a ray of light passing through a glass slag for different angles of incidence. The observations, likely to be correct are those of student. 1 / 10

a) IV b) III c) I d) II 6. A student traces the path of a ray of light passing through a rectangular glass slab. For measuring the angle of incidence, he must position the protractor in the manner as shown in figure. a) A b) B c) D d) C 7. In the set-up shown below, a clear image of a distant object is obtained on the screen. The focal length of the concave mirror is: a) 9.4 cm b) 9.9 cm c) 9.8 cm d) 11.4 cm 8. In the glass slab experiment shown below, four students A, B, C and D did the following: A : kept the eyes far from the glass slab while placing both the pins P3 and p4 B : kept the eyes close to the glass slab while placing both the pins P3 and P4 C : kept the eyes close to the glass slab while placing pin P3 and far from the slab while placing pin P4 D : kept the eyes far from the glass slab while placing pin P3 and close to the slab while placing pin P4 2 / 10

The correct procedure is that of student a) D b) B c) C d) A 9. Magnification produced by a rear view mirror fitted in vehicles a) is equal to one b) can be more than or less than one depending upon the position of the object in front of it c) is less than one d) is more than one 10. The nature of the image is not affected by the position of the object in a) convex mirror b) none of these c) concave lenses d) concave mirror 11. A student performs an experiment on 'tracing the path of a ray of light passing through a rectangular glass slab \"for different values of angle of incidence. He fixes pins P3 and P4, while looking through the face DC, so that their feet are in line with the images of the feet of the pins P1 and P2 : a) neither the feet nor the heads of the b) only the heads of the images of pins images of pins P3 and P4 are in line P3 and P4 are in line with the heads with the feet and heads, respectively, of pins P1 and P2 of pins P1 and P2. c) feet, as well as the heads of the d) only the feet of the images of pins P3 images of pins P3 and P4 are in line and P4 are in line with the feet of with the feet and heads respectively pins P1 and P2 of pins P1 and P2 12. Which of the following ray diagrams is correct for the ray of light incident on a concave mirror as shown in the figure? 3 / 10

a) b) c) d) 13. On covering a portion of a lens with a black sheet: a) size depending on the coverage area b) a full image is formed c) full image of reduced brightness is d) full image of increased brightness is formed formed 14. To determine the focal length of a concave mirror, a student focuses a distant object using the concave mirror. The best object can be: a) a distant tree b) All of these c) classroom window d) sun 15. As the incident angle is increased for a given pair of the medium, the refraction angle will a) decrease b) remain the same c) zero d) increase 16. Your school laboratory has one large window. To find the focal length of a concave mirror using one of the walls as the screen, the experiment may be performed: a) on the wall adjacent to the window b) on the same walls as the window c) only on the table as per the d) near the wall opposite to the window laboratory arrangement 17. Which of the following diagrams give a correct picture? a) b) c) d) 4 / 10

18. A ray passing through the focus and falling on a convex lens will: a) retrace its path b) will emerge parallel to the principal axis c) will emerge through a focus on d) will emerge perpendicular to the another side principal axis 19. An experiment to trace the path of a ray of light through a glass slab was performed by four students I, II, III and IV. They reported the following measurements of angle of incidence i, angle of refraction r and angle of emergence e. Which one of the students has performed the experiment correctly? Student Angle i Angle r Angle I 60o 35o 59o II 45o 40o 40o II 35o 30o 40o IV 50o 55o 50o a) III b) I c) II d) IV 20. A student determines the focal length of a device X, by focusing the image of a far off object on the screen positioned as shown in the figure below: The device X is a : a) Convex mirror b) Concave mirror c) Concave lens d) Convex lens 21. Assertion (A): An object is placed at a distance of f from a convex mirror of focal length f, its image will form at infinity. Reason (R): The distance of an image in a convex mirror can never be infinity. a) Both A and R are true and R is the b) Both A and R are true but R is not the correct explanation of A. correct explanation of A. c) A is true but R is false. d) A is false but R is true. 22. Assertion (A): Refractive index has no units. Reason (R): The refractive index is a ratio of two similar quantities. a) Both A and R are true and R is the b) Both A and R are true but R is not the correct explanation of A. correct explanation of A. c) A is true but R is false. d) A is false but R is true. 5 / 10

23. Which kind of mirrors are used in the headlights of a motor-car and why? 24. Name the type of mirror which always forms a virtual and diminished image. 25. You have a spherical mirror. The image of an object placed in front of the mirror is virtual. If the position of the object is charged, the image remains virtual end erect. Is the spherical mirror concave or convex? 26. Define the principle focus of a concave mirror. 27. Give the cartesian sign convention for: (a) height of a real image, and (b) height of a virtual image. 28. Define the term refraction of light. 29. If an object is placed at the focus of a concave mirror, where is the image formed? 30. Name the mirror that can give an erect and enlarged image of an object? 31. The rays, parallel to the principal axis, of a spherical mirror, actually meet at a point 20 cm distant from its pole. Identify the mirror and give its focal length. 32. Identify the device used as a spherical mirror or lens in case, when the image formed is virtual and erect in case. Object is placed between the focus and device, image formed is enlarged and on the same side as that of the object. 33. Define the term angle of incidence. 34. What is the unit of refractive index? 35. What is light? 36. Name the phenomena on which the working of a lens is based. 37. What is an optically denser medium? 38. What is a beam of light? 39. Define one dioptre of power of a lens? 40. What is relative refractive index? 41. Find out, from the given table, the medium having highest optical density. Also, find the medium with lowest optical density. Material medium Refractive index Material medium Refractive index Air 1.0003 Canada Balsam 1.53 Ice 1.31 Rock salt 1.54 Water 1.33 Carbon disulphide 1.63 Alcohol 1.36 Dense flint glass 1.65 Kerosene 1.44 Ruby 1.71 Fused quartz 1.46 Sapphire 1.77 Turpentine oil 1.47 Diamond 2.42 Benzene 1.50 Crown glass 1.52 42. Identify the device used as a spherical mirror or lens in case, when the image formed is virtual and erect in case. The object is placed between the device and its focus, the image formed is enlarged and behind it. 6 / 10

Section B 43. For the experiment on finding the focal length of a convex lens by obtaining the image of a distant object, a laboratory assistant keeps the following apparatus on the table: A. A stand with a metal needle fixed in it B. A stand with the given convex lens fitted in it C. A thick cardboard white screen D. A metre scale A student can do the experiment by using the apparatus listed as a) D, A, B b) B, C, D c) A, B, C d) C, D, A 44. For the given data showing object distance and focal length of three concave mirrors, answer the following question : S. No. object distance (cm) focal length (cm) 1 30 20 2 10 15 3 20 10 Which mirror is being used as a make-up mirror? a) Case II b) Case I c) Case III d) Case I and III 45. While performing an experiment on determining the focal length of a convex lens, a student obtains a sharp inverted image of the laboratory window grill on the screen and measures the distance d between the screen and the lens. She then repeats the experiment and takes a distant tree as the object in the second case. In order to get a sharp image on the screen, she will now need to move the screen: a) very close to the lens b) slightly nearer to the lens c) very far away from the lens d) slightly farther away from the lens 46. A student focuses the image of a candle flame on a white screen by placing the flame at various distances from a convex lens. He noted his observation in the following table : Distance of the flame from lens(cm) Distance of the screen from lens (cm) 60 20 40 24 30 30 24 40 12 70 What is the focal length of convex lens? a) 20 b) 15 7 / 10

c) 12 d) 30 47. In an experiment on tracing the path of a ray of light through a rectangular glass slab, four students A, B, C, D, used the following values of angle of incidence and the distance between the feet of the two pins (fixed on the incident ray): A. (20o, 45o, 60o) and 1 cm B. (30o, 45o, 60o) and 6 cm C. (20o, 50o, 80o) and 10 cm D. (20o, 50o, 80o) and 15 cm Out of these, the best choice is that of student: a) D b) C c) A d) B 48. A student has to perform an experiment on tracing the path of a ray of light passing through a rectangular glass slab for three different angles of incidence. Four of his friends suggest the following options to him: A. Draw the incident rays corresponding to 20o, 50o, and 70o as the angles of incidence and fix the two pins on the incident rays just 2 cm apart. B. Draw the incident rays corresponding to 20o, 45o, and 70o as the angles of incidence and fix the two pins on the incident rays nearly 8 cm apart. C. Draw the incident rays corresponding to 30o, 45o, and 60o as the angles of incidence and fix the two pins on the incident rays nearly 8 cm apart. D. Draw the incident rays corresponding to 30o, 45o and 60o as the angles of incidence and fix the two pins on the incident rays nearly 2 cm apart. The best option that he should follow is the option a) C b) A c) B d) D 49. A student suggested the following guidelines to his friend for doing the experiment on tracing the path of a ray of light, passing through a rectangular glass slab, for three different angles of incidence: A. Draw the outline of the glass slab at three positions on the drawing sheet. B. Draw normals on the top side of these outlines near their left end. C. Draw the incident rays on the three outlines in directions making angles of 30o, 45o, 60o with the normal drawn. D. Look for the images of the feet of these pins while fixing two pins, from the other side, to get the refracted ray. When he showed these guidelines to his teacher, the teacher told him that two of them need to be corrected and modified. These two guidelines are: a) D and E b) C and D c) B and C d) B and D 8 / 10

50. On the basis of their experiment to trace the path of a ray of light passing through a rectangular glass slag four students arrived at the following interpretations: A. The angle of incidence is greater than the angle of emergence B. The angle of emergence is less than the angle of refraction C. Emergent ray is parallel to the incident ray D. Emergent ray is parallel to the refracted ray The correct interpretation is that of the student a) (A) b) (B) c) (C) d) (D) 51. A teacher gives a convex lens and a concave mirror of the focal length of about 20 cm each to his student and asks him to find their focal lengths by obtaining the image of a distant object. The student uses a distant tree as the object and obtains its sharp image, one by one, on a screen. The distances d1 and d2 between the lens/mirror and the screen in the two cases and the nature of their respective sharp images are likely to be: a) (20 cm, 20 cm) and (inverted, b) (20 cm, 40 cm) and (erect, erect) inverted) c) (20 cm, 40 cm) and (inverted, erect) d) (20 cm, 20 cm) and (erect, inverted) 52. In an experiment to determine the focal length of a convex lens, a student obtained a sharp inverted image of a distant tree on the screen behind the lens. She then removed the screen and looked through the lens in the direction of the object. She will see: a) an inverted image of the tree at the b) an erect image of the tree on the lens focus of the lens c) a blurred image on the wall of the d) no image as the screen has been laboratory removed Section C 53. State True or False: a) The incident ray, the normal to the surface at the point of incidence and the reflected ray, all lie in the same plane. b) Magnification is expressed as the ratio of the height of the image to the height of the object. c) A transparent material bound by two surfaces, of which one or both surfaces are spherical, forms a lens. 54. Observe the following incomplete ray diagram of an object where the image A'B' is formed after refraction from a convex lens. On the basic of above information fill in the blanks. i. The position of object AB would have been... ii. Size of the object would have been ... than the size of image. 9 / 10

55. An object 3 cm high is placed 20 cm from convex lens of focal length 12 cm. Find the nature, position and height of the image. 56. Light enters from air to glass having refractive index 1.50. What is the speed of light in glass? Speed of light in vacuum is 3 ×108 ms-1. 57. An object is kept at a distance of 18 cm, 20 cm and 30 cm, from a lens of power+5D. (i) In which case or cases would you get a magnified image? (ii) Which of the magnified image can we get on a screen? (b) List two widely used applications of a convex lens. Section D 58. Read the following and answer any four questions: In the concave mirror, the nature, position and size of the image formed depend on the position of the object in relation to pole, the centre of curvature and focus. The image is real for some position of the object and virtual for another position. The image is either magnified, reduced, or has the same size, depending on the object's position. i. What will be the position of the image if the object is placed at infinity? a. Beyond C b. Between F and C c. At infinity d. At the focus F ii. For an image to be the same size as the object what will be the position of the object? a. At F b. At C c. Between C and F d. Beyond C iii. If the image formed behind a concave mirror what will be the nature of the image? a. Virtual b. Erect c. Both (a) and (b) d. none of the above iv. Highly diminished point-size image is formed a. At the focus F b. At infinity c. Behind the mirror d. At C v. If the object is placed at F size of the image is ________ a. Same size b. Enlarged c. Highly enlarged d. Diminished 10 / 10