 # NCERT Exemplar Solution for CBSE Class 10 Science Chapter: Light‒Reflection and Refraction (Part-I)

In this article you will get CBSE Class 10 Science chapter 10, Light ‒ Reflection and Refraction: NCERT Exemplar Problems and Solutions (Part-I). Every question has been provided with a detailed explanation. All the questions given in this article are very important to prepare for CBSE Class 10 Board Exam 2017-2018. Here you get the CBSE Class 10 Science chapter 10, Light ‒ Reflection and Refraction: NCERT Exemplar Problems and Solutions (Part-I). This part of the chapter includes solutions for Question No.1 to 19 from the NCERT Exemplar Problems for Class 10 Science Chapter: Light ‒ Reflection and Refraction. These questions include only the Multiple Choice Questions (MCQs) framed from various important topics in the chapter. Each question is provided with a detailed explanation.

CBSE Class 10 Science Syllabus 2017-2018

NCERT Exemplar problems are a very good resource for preparing the critical questions like Higher Order Thinking Skill (HOTS) questions. All these questions are very important to prepare for CBSE Class 10 Science Board Examination 2017-2018 as well as other competitive exams.

Find below the NCERT Exemplar problems and their solutions for Class 10 Science Chapter, Light ‒ Reflection and Refraction:

Multiple Choice Questions (MCQs)

Question. 1 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 to each other

(d) Concave mirror as well as concave lens

Explanation: When a point light source is placed at the focus of concave mirror then it all light rays after reflection through mirror will become parallel to the principal axis.

When this point light source is placed at the focus of convex lens then after falling on convex lens it will become parallel to the principal axis.

Question. 2 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

Explanation: Here, size of object = O = + 10.0 mm = + 1.0 cm (as, 1 cm = 10 mm)

Size of Image size = I = 5.0 mm = 0.5 cm

Image distance, v = − 30 cm   (as image is real)

Let, object distance = u

Focal length, f =? NCERT Solutions for CBSE Class 10 Science

Question. 3 Under which of the following conditions, a concave mirror can form an image larger than the actual object?

(a) When the object is kept at a distance equal to its radius of curvature

(b) When object is kept at a distance less than its focal length

(c) When object is placed between the focus and centre of curvature

(d) When object is kept at a distance greater than its radius of curvature

Explanation: A concave mirror can form an image larger than the actual object when the object is placed between the focus and centre of curvature.

Image formation is shown below, where object (AB) is placed between the focus and centre of curvature for which image (A’B’) is obtained behind the mirror. Question. 4 Figure shows a ray of light as it travels from medium A to medium B. Refractive index of the medium B relative to medium A is Explanation: Here, angle of incidence = i = 60o

Angle of refraction = r = 450 Question. 5 A light ray enters from medium A to medium B as shown in the figure. The refractive index of medium B relative to A will be (a) Greater than unity

(b) Less than unity

(c) Equal to unity

(d) Zero

Explanation: Since light rays in medium B goes towards normal. So it has greater restrictive index and lesser velocity of light with respect to medium A. So refractive index of medium B with respect to medium A is greater than unity.

Question. 6 Beams of light are incident through the holes A and B and emerge out of box through the holes C and D respectively as shown in the figure. Which of the following could be inside the box? (a) A rectangular glass slab

(b) A convex lens

(c) A concave less

(d) A prism

Explanation:  In the given figure, emergent light rays are parallel to the direction of incident light rays. Out of the given options only a rectangular glass slab can change the path of light ray in such a way that emergent rays are parallel to the incident rays.

Question. 7 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) Concave lens

(b) Rectangular glass slab

(c) Prism

(d) Convex lens

Explanation: In the given diagram, parallel rays converge at a point and emerges from face B. So, there will be a convex lens inside the box. Question. 8 Which of the following statements is true?

(a) A convex lens has 4 dioptre power having a focal length 0.25 m

(b) A convex lens has 4 dioptre power having a focal length – 0.25 m

(c) A concave lens has 4 dioptre power having a focal length 0.25 m

(d) A concave lens has 4 dioptre power having a focal length – 0.25 m

Explanation: The power (P) of a lens of focal length (f) is given by P = 1/f , where f is the focal length meter and power in dioptre.

Now, P = 1/ff = 1/P = 1/4 = 0.25 m.

Question. 9 Magnification produced by a rear view mirror fitted in vehicles

(a) is less than one

(b) is more than one

(c) is equal to one

(d) can be more than or less than one depending upon the position of the object in front of it.

Explanation: Convex mirror is used as rear view mirror in vehicles. It forms virtual, erect and diminished images of the objects.

As, magnification is ratio of height of image to the height of the object, hence, magnification produced by a rear view mirror fitted in vehicles is less than one.

Question. 10 Rays from sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object?

(a) 15 cm in front of the mirror

(b) 30 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

Explanation: Sun is at infinite distance from the surface of the earth.

Now light rays from sun rays after reflection from concave mirror will converge at focus.

It is given that sunrays converge at 15 cm. So, focal length of the mirror = f = 15 cm.

In case of a concave mirror, the size of image and object will be same if the object is placed at 2f. Hence, in this case object must be place at 2f or 2 × 15 = 30 cm.

Question. 11 A full length image of a distant tall building can definitely be seen by using

(a) a concave mirror

(b) a convex mirror

(c) a plane mirror

(d) both concave as well as plane mirror

Explanation: A convex mirror forms virtual, erect and diminished image of the objects. So, out of given options, distant tall building can definitely be seen by using a convex mirror.

Question. 12 In torches, search lights and headlights of vehicles, the bulb is placed

(a) between the pole and the focus of the reflector

(b) very near to the focus of the reflector

(c) between the focus and centre of curvature of the reflector

(d) at the centre of curvature of the reflector

Explanation: In torches, search lights and headlights of vehicles, the bulb is placed very near to the focus of the reflector (or concave mirror).

It is due the reason that light rays after falling on reflecting surface become parallel to the principal axis of the mirror, and a concentrated beam of light is obtained.

Question. 13 The laws of reflection hold good for

(a) plane mirror only

(b) concave mirror only

(c) convex mirror only

(d) all mirrors irrespective of their shape

Explanation: The laws of reflection holds good for light reflected form any smooth surface i.e., all mirrors regardless of its shape.

Question. 14 The path of a ray of light coming from air passing through a rectangular glass slab traced by four students shown as A, B, C and D in the figure. Which one of them is correct? (a) A

(b) B

(c) C

(d) D

Explanation: When a light ray is passed through a glass slab obliquely then, emergent ray will be parallel to the direction of the incident ray.

Question. 15 You are given water, mustard oil, glycerine and kerosene. In which of these media, a ray of light incident obliquely at some angle would bend the most.

(a) Kerosene

(b) Water

(c) Mustard oil

(d) Glycerine

Explanation: Out of the given four materials, the refractive index of glycerine is highest. So, greatest deviation of incident light ray is observed in case of glycerine.

Question. 16 Which of the following ray diagrams is correct for the ray of light incident on a concave mirror as shown in figure? (a) Fig. A

(b) Fig. B

(c) Fig. C

(d) Fig. D

Explanation: Ray of light going parallel to the principal axis towards the mirror after reflection will pass through the focus. So, figure D is correct.

Question. 17 Which of the following ray diagrams is correct for the ray of light incident on a lens shown in figure? (a) Fig. A

(b) Fig. B

(c) Fig. C

(d) Fig. D

Explanation: When a light ray passing through focus will fall on convex lens then, the emergent ray of light will become parallel to the principal axis. So, figure A is correct.

Question. 18 A child is standing in front of a magic mirror. She finds the image of her head bigger, the middle portion of her body of the same size and that of the legs smaller. The following is the order of combinations for the magic mirror from the top.

(a) Plane, convex and concave

(b) Convex, concave and plane

(c) Concave, plane and convex

(d) Convex, plane and concave

Explanation: Her head appears large; it means concave mirror of large focal length is used at the top.

Her middle body appears of the same size in the mirror. It means plane mirror is used in the middle.

Her legs appear smaller. It means convex mirror is used below plane mirror. Hence, option (c) is the correct combination.

Question. 19 In which of the following, the image of an object placed at infinity will be highly diminished and point sized?

(a) Concave mirror only

(b) Convex mirror only

(c) Convex lens only

(d) Convex mirror, convex mirror, concave lens and convex lens