CHAPTER- 9-LIGHT REFLECTION AND REFRACTION

CHAPTER- 9-LIGHT REFLECTION AND REFRACTION

WORKSHEET – 1 (VOLUME-01)

TIME-40 MIN
MM=34 M

SECTION- A :MCQ (1X5=5M)

  1. A doctor uses a head mirror to focus light on the internal body parts such as teeth, ear, nose and throat. Which mirror is it?
    a. Plane
    b. Parabolic
    c. Convex
    d. Concave
  2. The path of a ray of light coming from air passing through a rectangular glass slab traced by four students is shown as A, B, C and D in the figure. Which one of them is correct –
    Ray of light passing through rectangular glass slab A, B, C, D
    a. A
    b. B
    c. C
    d. D
  3. The SI unit of power of lens is:
    a. Metre
    b. Centimetre
    c. dioptre
    d. \( m^{-1} \)

In ( Q.no.4 & 5) a statement of Assertion is followed by a statement of reason . Mark the correct choice as :
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) Assertion is true but R is false.
(d) R is true but A is false.

  1. Assertion: Refractive index has no units.
    Reason : The refractive index is a ratio of two similar quantities.
  2. Assertion: A virtual image cannot be photographed.
    Reason : Real objects can be photographed.

SECTION B : VERY SHORT ANSWER QUESTIONS (2MX3=6M)

  1. Draw a ray diagram to show the refraction of light through a glass prism. Mark on it:
    (a) the incident ray
    (b) the emergent ray
    (c) the angle of deviation

  2. Mirror surface with incident and reflected ray, angle 35 degrees with surface
    a) Find the angle of incidence and angle of reflection from the diagram.
    b) Define reflection of light.

  3. Ray diagram for concave mirror
    a. Redraw the diagram given below in your answer book and show the direction of the light ray after reflection from the mirror.
    b. If the image formed by a spherical mirror for all positions of the object placed in front of it is always erect and diminished, what type of mirror is it?

SECTION C : Short answer questions ( 3MX3=9M)

  1. a) State Snell’s laws of refraction.
    b) When a ray of light travelling in air enters obliquely into a glass slab, it is observed that the light ray emerges
    Diagram showing refraction through glass slab with angles i, r, e
  2. Write one similarity and one dissimilarity between image formed by plane mirror and convex mirror. State two uses of convex mirror.
  3. a) Following diagram shows the formation of image of an object placed at 2F1, Mention the type of lens used and nature of the image.
    Ray diagram of lens with object at 2F1
    b) The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

SECTION D : Long answer questions ( 5MX2=10M))

  1. (a) Define the following terms in the context of spherical mirrors:
    (i) Pole
    (ii) Centre of curvature
    (b) Draw ray diagrams to show the principal focus of a:
    (i) Concave mirror
    (ii) Convex mirror
    Diagram with mirror M, object P, image Q
    (c) Consider the following diagram in which M is a mirror and P is an object and Q is its magnified image formed by the mirror. State the type of the mirror M and one characteristic property of the image.
  2. The ability of a medium to refract light is also expressed in terms of its optical density. optical density has a definite connotation. It actually means optically rarer medium and optically denser medium. The one with the larger refractive index is optically denser medium lower refractive index is Optically rarer. The speed of light varies in both medium.
    a) What is optical density?
    b) What is an optically rarer medium?
    c) What happens to a ray of light if it travels from an Optically denser to an Optically rarer medium?
    d) If light ray passes from glass to water what is the speed of light?

SECTION D : Case based questions (4MX1=4M)

  1. CASE : The spherical mirror forms different types of images when the object is placed at different locations. When the image is formed on screen, the image is real and when the image does not form on screen, the image is virtual. When the two reflected rays meet actually, the image is real and when they appear to meet, the image is virtual.
    A concave mirror always forms a real and inverted image for different positions of the object. But if the object is placed between the focus and pole. the image formed is virtual and erect.
    A convex mirror always forms a virtual, erect and diminished image. A concave mirror is used as doctor’s head mirror to focus light on body parts like eyes, ears, nose etc., to be examined because it can form erect and magnified image of the object. The convex mirror is used as a rear-view mirror in automobiles because it can form a small and erect image of an object.

    (i) When an object is placed at the centre of curvature of a concave mirror, the image formed is :
    (a) larger than the object
    (b) smaller than the object
    (c) same size as that of the object
    (d) highly enlarged

    (ii) No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be :
    (a) plane
    (b) concave
    (c) convex
    (d) either plane or convex.

    (iii) 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

    (iv) To get an image larger than the object, one can use :
    (a) convex mirror but not a concave mirror
    (b) a concave mirror but not a convex mirror
    (c) either a convex mirror or a concave mirror
    (d) a plane mirror

ANSWERS

1. d
2. b
3. c. dioptre
4. (a) Both assertion (A) and (R) are true and reason (R) is the correct explanation of assertion (A).
5. (d) Assertion (A) is false but the reason (R) is true.
6. [Diagram Required]
7. a) 55⁰, 55⁰ as the angle of incidence is equal to angle of reflection.
b) Reflection of light is the process of bouncing back light rays in the same medium when it strikes the smooth and shiny reflecting surface.
8. a) [Diagram Required]
b) Convex mirror
9. a) Snell' law of refraction is:- "the ratio of sine of angle of incident to sine of angle of refraction is always constant for given medium"
where, \( \sin i / \sin r = n \) (constant)
10. Similarity: - Both produce Virtual Image.
Dissimilarity:- Convex Mirror produces diminished image while plane mirror produce the image of the same size as that of the object.
Uses: 1. Rear view mirror 2. In street lights
11. a) convex lens, the image is real and inverted
b) We know that \( f = R/2 \) therefore , \( f = 20/2 = 10 \text{ cm} \)
12. a) i) Pole – Centre of the reflecting surface of the mirror.
ii) Centre of curvature – The centre of the hollow sphere of which the reflecting surface of mirror forms a part.
b) i) [Diagram: Concave mirror focus]
ii) [Diagram: Convex mirror focus]
c) Concave mirror
Image formed is virtual
13. a) The ability of a medium to refract light.
b. A medium in which speed of light is more.
c. It bends away from the normal.
d. The speed of light increases
14. i.(c) same size as that of the object
ii.(d) either plane or convex.
iii.(c) Concave, plane and convex
iv.(b) a concave mirror but not a convex mirror

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