CBSE Class 10 Science HOTs Reflection and Refraction Set 02

Reflection of Light

Question. Multiple Choice Questions (1 Mark): The things visible to us due to the presence of
(a) object
(b) light
(c) dark
(d) None of the options
Answer: (b) light

Question. Which of the following phenomenon is not associated with light?
(a) Image formation by mirror
(b) Twinkling of stars
(c) Formation of rainbow
(d) Magnetic field lines
Answer: (d) Magnetic field lines

Question. Which of the following is incorrect about the properties of light?
(a) Straight-line propagation of light
(b) Light is a form of energy
(c) Light needs a medium to propagate
(d) It has a finite speed
Answer: (c) Light needs a medium to propagate. Light is an electromagnetic wave in nature which do not require any medium for its propagation.

Question. The light incident on a highly polished surface rebound into the same medium in same or different direction, is called
(a) reflection of light
(b) refraction of light
(c) scattering of light
(d) None of the options
Answer: (a) reflection of light

Question. Image formed by the plane mirror is
(a) virtual, diminished and behind the mirror
(b) virtual, erect, same size and behind the mirror
(c) real, same size, formed on the same side of the object.
(d) virtual, erect, enlarged and behind the mirror
Answer: (b) virtual, erect, same size and behind the mirror

Question. Which type of mirror is used to get a virtual, erect, laterally inverted and same size image as that of object?
(a) Convex mirror
(b) Concave mirror
(c) Plane mirror
(d) All of the options
Answer: (c) Plane mirror

Question. In reflection of light, the angle of reflection is _______ the angle of incidence.
(a) equal to
(b) greater than
(c) less than
(d) cannot say
Answer: (a) equal to

Question. The angle between the incident ray and reflected ray is \( 60^\circ \), the angle of incidence is
(a) \( 60^\circ \)
(b) \( 45^\circ \)
(c) \( 30^\circ \)
(d) \( 90^\circ \)
Answer: (c) \( 30^\circ \). (As \( \angle i + \angle r = 60^\circ \), but \( \angle i = \angle r \implies \angle i = 30^\circ \))

Question. A ray of light is incident on a plane reflecting surface at angle of incidence of \( 30^\circ \). Then the reflected ray is deviated by an angle equal to
(a) \( 30^\circ \)
(b) \( 150^\circ \)
(c) \( 60^\circ \)
(d) \( 120^\circ \)
Answer: (d) \( 120^\circ \). (Angle of deviation of reflected ray \( = 60^\circ + 30^\circ + 30^\circ = 120^\circ \))

Question. The angle of incidence for a ray of light having zero reflection angle is
(a) \( 90^\circ \)
(b) \( 45^\circ \)
(c) \( 30^\circ \)
(d) \( 0^\circ \)
Answer: (d) \( 0^\circ \)

Very Short Answer Type Questions 

Question. State the two laws of reflection of light.
Answer: Laws of reflection of light:
(i) The angle of incidence is equal to the angle of reflection.
(ii) The incident ray, the normal to the reflecting surface at the point of incidence and reflected ray from that point, all lies in the same plane.

Question. List four characteristics of the images formed by plane mirrors. 
Answer: Characteristics of image formed by a plane mirror:
(i) It is always virtual and erect.
(ii) The size of image is equal to that of the object.
(iii) The image is formed at the same distance behind the mirror as the object is in front of the mirror.
(iv) The image is laterally inverted.

Spherical Mirrors

Question. Multiple Choice Questions (1 Mark): The surface of the spoon curved inwards can be approximated to
(a) convex mirror
(b) concave mirror
(c) plane mirror
(d) concavo convex mirror
Answer: (b) concave mirror

Question. The centre of the reflecting surface of a spherical mirror is a point called
(a) centre of curvature
(b) focus
(c) pole
(d) None of the options
Answer: (c) pole

Question. Centre of curvature of a convex mirror lies
(a) behind the mirror
(b) infront of the mirror
(c) at the surface of the mirror any where
(d) at infinity
Answer: (a) behind the mirror

Question. Principal axis of a spherical mirror is always normal to the mirror at its
(a) focus
(b) pole
(c) centre of curvature
(d) both (a) and (c)
Answer: (b) pole

Question. Diameter of the reflecting surface of spherical mirror is called
(a) radius of curvature
(b) focal length
(c) aperture
(d) both (a) and (b)
Answer: (c) aperture

Question. A concave mirror of radius \( 30 \text{ cm} \) is placed in water. It’s focal length in air and water differ by
(a) 15
(b) 20
(c) 30
(d) 0
Answer: (d) 0. The focal length of spherical mirror does not depends on the surrounding medium.

Question. A real image is formed by the light rays after reflection or refraction when they: (A) actually meet or intersect with each other. (B) actually converge at a point. (C) appear to meet when they are produced in the backward direction. (D) appear to diverge from a point. Which of the above statements are correct? 
(a) (A) and (D)
(b) (B) and (D)
(c) (A) and (B)
(d) (B) and (C)
Answer: (c) (A) and (B)

Very Short Answer Type Questions 

Question. (a) Explain why a ray of light passing through the centre of curvature of a concave mirror, gets reflected along the same path. (b) State the type of mirror that can make a parallel beam of light when light from a point source is incident on it. At what location on the principal axis, this point source is placed?
Answer: (a) The ray passing through the centre of curvature incident to the mirror along its normal, so \( \angle i = \angle r = 0 \). Therefore, the ray retraces its path. (b) Concave mirror. At focus.

Question. Define the radius of curvature of spherical mirrors. Find the nature and focal length of a spherical mirror whose radius of curvature is \( +24 \text{ cm} \).
Answer: Radius of Curvature: The separation between the pole (P) and the centre of curvature (C) or the radius of the hollow sphere, of which the mirror is a part, is called radius of curvature (R), i.e., \( PC = R \).
Given, \( R = 2f = 24 \text{ cm} \)
Therefore, \( f = +12 \text{ cm} \)
The focal length of the mirror is positive. This indicates that nature of the given spherical mirror is convex/diverging mirror.

Short Answer Type Questions 

Question. Define the following terms in the context of spherical mirrors: (i) Pole (ii) Centre of curvature (iii) Principal axis (iv) Principal focus
Answer:
(i) Pole: The central point of the reflecting spherical surface is called the pole (P). It lies on the surface of the mirror.
(ii) Centre of Curvature: The centre of the hollow sphere of which the spherical mirror is a part, is called the centre of curvature (C).
(iii) Principal Axis: The straight line joining the pole and the centre of curvature is called the principal axis.
(iv) Principal Focus: The point ‘F’ on the principal axis, where the incident light rays parallel to the principal axis actually meet (converge) (in case of a concave mirror) or appear to diverge or come from (in case of a convex mirror) after reflection, is called its principal focus (F).

Question. State any three difference between real image and virtual image formed by a spherical mirror.
Answer:
Real Image
(i) After reflection from the mirror, the light rays are actually meet or intersect.
(ii) Image can be obtained on the screen.
(iii) The real image is always inverted and formed below the principal axis.
(iv) It is always formed in front of the spherical mirror/lens.

Virtual image
(i) After reflection from the mirror, the light rays do not intersect but appear to meet at a point.
(ii) Image cannot be obtained on the screen.
(iii) The virtual image is always erect and formed above the principal axis.
(iv) It is always formed behind the spherical mirror/lens.

PRACTICE QUESTIONS

Question. Centre of curvature of a spherical mirror is
(a) not a part of the mirror
(b) lies outside its reflecting surface
(c) both (a) and (b)
(d) neither (a) nor (b)
Answer: (c) both (a) and (b)

Question. A student obtained a bright and sharp image of a sun by using a concave mirror and exposed to it sunlight for some time, it catches fire because
(a) reflected ray has more energy
(b) the heat produced due to the concentration of sunlight at the focus of a concave mirror ignites the paper.
(c) high temperature of atmosphere able to burn the paper itself and sun rays have no role.
(d) none of the options
Answer: (b) the heat produced due to the concentration of sunlight at the focus of a concave mirror ignites the paper.

Question. The relation \( R = 2f \) is valid:
(a) For concave mirrors but not for convex mirrors
(b) For convex mirrors but not for concave mirrors
(c) Neither for concave mirrors nor for convex mirrors
(d) For both concave and convex mirrors
Answer: (d) For both concave and convex mirrors

Question. (a) Where the principal focus of a spherical mirror lies exactly?
(b) If the radius of curvature of a concave mirror is twice that of convex mirror, what is the ratio of their focal length?
Answer: (a) The principal focus of a spherical mirror lies exactly at the midpoint of the line joining the pole (P) and the centre of curvature (C).
(b) Since \( f = R/2 \), the focal length is directly proportional to the radius of curvature. Therefore, if the radius of curvature of the concave mirror is twice that of the convex mirror, the ratio of their focal lengths is 2:1.

Question. (a) Define focal length of spherical mirror.
(b) How we can we find an approximate focal length of a concave mirror? Give reason.
Answer: (a) Focal length: The distance between the pole and the principal focus of a spherical mirror is called its focal length.
(b) We can find an approximate focal length by focusing a distant object (like the sun) onto a screen. The distance between the mirror and the sharp image on the screen is the approximate focal length because light rays from a distant object are parallel to the principal axis and converge at the focus after reflection.

Multiple Choice Questions 

Question. 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

Question. For a real object, which of the following can produce a real image?
(a) Plane mirror
(b) Concave mirror
(c) Concave lens
(d) Convex mirror
Answer: (b) Only concave mirror can produces a real image for the any position of object between its focus and infinity.

Question. The nature of the image formed by concave mirror when the object is placed between the focus (F) and centre of curvature (C) of the mirror observed by us is
(a) real, inverted and diminished
(b) virtual, erect and smaller in size
(c) real, inverted and enlarged
(d) virtual, upright and enlarged
Answer: (c) When object lies between C and F, the real, inverted and enlarged image is formed beyond C.

Question. The radius of curvature of a converging mirror is 30 cm. At what distance from the mirror should an object be placed so as to obtain a virtual image? 
(a) Infinity
(b) 30 cm
(c) Between 15 cm and 30 cm
(d) Between 0 cm and 15 cm
Answer: (d) Between 0 cm and 15 cm

Question. An object at a distance of 30 cm from a concave mirror gets its image at the same point. The focal length of the mirror is
(a) – 30 cm
(b) 30 cm
(c) – 15 cm
(d) +15 cm
Answer: (c) – 15 cm
When object is placed at 2F, the image formed by concave mirror is also at 2F. So \( 2f = –30 \) or \( f = –15 \text{ cm} \).

Very Short Answer Type Questions

Question. List four properties of the image formed by a concave mirror, when object is placed between focus and pole of the mirror.
Answer: (i) Behind the mirror
(ii) Enlarged, i.e. magnified
(iii) Virtual
(iv) Erect

Question. “A concave mirror of focal length 15 cm can form a magnified erect as well as inverted image of an object placed in front of it.” Justify this statement stating the position of the object with respect to the pole of the mirror in both cases for obtaining the images.
Answer: (i) When the object is placed between P (pole) and F (focus) of the concave mirror, we get a magnified and erect image.
(ii) When the object is placed between C (centre of curvature) and F (focus), we get a magnified and inverted image.

Question. Under which of the following condition(s) a concave mirror can form an enlarged image?
(a) At C
(b) At F
(c) Between C and F
(d) Beyond C
Answer: (c) Between C and F

Question. The image formed by concave mirror is real for the position of object
(a) at infinity
(b) at centre of curvature
(c) at its focus
(d) all of the options
Answer: (d) all of the options

Image Formation by Convex Mirror

Multiple Choice Questions 

Question. The nature of image formed by a convex mirror when the object distance from the mirror is less than the distance between pole and focal point (F) of the mirror would be
(a) real, inverted and diminished in size
(b) real, inverted and enlarged in size
(c) virtual, upright and diminished in size
(d) virtual, upright and enlarged in size
Answer: (c) virtual, upright and diminished in size
Convex mirror always forms a virtual, erect diminished image irrespective of the position of object in front of it.

Question. An object at a distance of +15 cm is slowly moved towards the pole of a convex mirror. The image will get
(a) shortened and real
(b) enlarged and real
(c) enlarge and virtual
(d) diminished and virtual
Answer: (d) diminished and virtual
Convex mirror always formed virtual and diminished image.

Question. On moving the object from infinity towards the pole of the convex mirror, the image moves from
(a) focus towards pole
(b) focus towards centre of curvature
(c) pole to infinity on the same side of object
(d) focus to infinity behind the mirror
Answer: (a) focus towards pole

Question. If the object moves away from the pole of a convex mirror, then, the size of image gradually changes from
(a) highly enlarged to enlarged
(b) diminished to point size
(c) highly diminished to diminished
(d) highly diminished to same size of object
Answer: (b) diminished to point size

Very Short Answer Type Questions

Question. List four specific characteristics of the images of the object formed by convex mirrors. 
Answer: Properties of image formed by a convex mirror:
(i) It always formed behind the mirror, between the pole and its focus.
(ii) The image is always virtual and erect.
(iii) The size of image is always smaller than the object.
(iv) Magnification is always positive.

Question. The focal length of a convex mirror is 12.5 cm. How far is its centre of curvature (i) from the pole (ii) from the focus.
Answer: The centre of curvature of a mirror is always located at a distance equal to its radius of curvature which is twice of its focal length. So, (i) the centre of curvature is 25 cm away from its pole and (ii) from the focus, it is 12.5 cm away.