61. The focal length of a concave lens is considered to be ____________ .
Answer/Explanation
Answer:
Explanation: negative
62. In order to calculate the power of a lens, we need its focal length in ____________ .
Answer/Explanation
Answer:
Explanation: metres
63. Angle of refraction cannot exceed 90°. [True/False]
Answer/Explanation
Answer:
Explanation: True
64. When incident angle i satisfies n = 1sini, the refracted light will pass along the surface. [True/False]
Answer/Explanation
Answer:
Explanation: True
65. A person standing in front of a mirror finds his image larger than himself. This shows that mirror is convex in nature. [True/False]
Answer/Explanation
Answer:
Explanation: False
Convex mirror always forms a diminished image so it is false statement.
i.e., the object distance from the mirror is numerically equal to (m – 1 )f.
66. Lateral displacement increases with the thickness of the given slab. [True/False]
Answer/Explanation
Answer:
Explanation: True
67. Lateral displacement is directly proportional to thickness of the glass slab. [True/False]
Answer/Explanation
Answer:
Explanation: True
68. Nature of image formed by mirror gives an ideal about nature of mirror. [True/False]
Answer/Explanation
Answer:
Explanation: True
69. A convex lens (ng = 3/2) when placed in water (nw = 4/3) has increased focal length [True/False]
Answer/Explanation
Answer:
Explanation: True
70. A convex and a concave lens of equal focal length behaves as a regular glass slab receiving light normally. [True/False]
Answer/Explanation
Answer:
Explanation: False
71. Concave lens and convex mirror diverge the rays which fall parallel to the principal axis. [True/False]
Answer/Explanation
Answer:
Explanation: True
72. The power of a concave lens is positive. [True/False]
Answer/Explanation
Answer:
Explanation: False
Direction: Match Column I with Column II.
73.
| Column I | Column II |
| (i) Ray through centre of curvature | (A) Reflected parallel to principal axis |
| (ii) Ray through focus | (B) Converge at focus |
| (iii) Rays from infinite distance | (C) Emerge through focus |
| (iv) Refracted rays to infinity | (D) Retracing in mirrors |
Answer/Explanation
Answer:
Explanation:
(i) → (D), (ii) → (A), (iii) → (B), (iv) → (C)
(i) → (D): For this ray Zi = Zr = 0
(ii) → (A): The ray of light passing through the focus will emerge parallel to the principal axis after reflection.
(iii) → (B): When object is at infinity, the image is formed at the focus of a concave mirror.
(iv) → (C): A ray from the object parallel to principal axis will pars through the principal . focus after refraction in a convex lens.
74. What is light?
Answer/Explanation
Answer:
Explanation:
Light is a form of energy. It brings the sensation of sight. It is a form of electromagnetic radiation. It also provides us means of communication (fibre-optics).
75. Write any one observation from everyday life which show us that light travels in a straight line.
Answer/Explanation
Answer:
Explanation:
A small source of light costs a sharp shadow of an opaque object tells us that light travels in a straight line.
76. What is a ray?
Answer/Explanation
Answer:
Explanation:
Ray is a line defining the path of light.
77. What is beam?
Answer/Explanation
Answer:
Explanation:
A bundle of rays originating from the same source of light in a particular direction is called beam of light.
78. Explain why a ray of light passing through the centre of curvature of a concave mirror, gets reflected along the same path.
Answer/Explanation
Answer:
Explanation:
The ray passing through the centre of curvature incident to the mirror along its normal, so ∠i = ∠r = 0. Therefore, the ray retraces its path.
79. Is light a ray or a wave?
Answer/Explanation
Answer:
Explanation:
It is considered in both the forms.
80. What are the characters associated with light as a wave?
Answer/Explanation
Answer:
Explanation:
Frequency and wavelength.
81. What is Spherical mirror?
Answer/Explanation
Answer:
Explanation:
A reflecting surface which is of the form of a sphere (hollow) in which inner or outer surface is reflecting.
82. What is the relation connecting focal length and radius of a spherical mirror?
Answer/Explanation
Answer:
Explanation: F = R2
83. Can any spherical surface act as a reflector?
Answer/Explanation
Answer:
Explanation:
Yes, polished surface can be better reflectors.
84. Redraw the diagram given below in your answer book and show the direction of the light ray after reflection from the mirror.
Answer/Explanation
Answer:
Explanation:
85. For what position of object, a concave mirror forms a real image equal to size of object?
Answer/Explanation
Answer:
Explanation:
When object is placed at the centre of curvature (C) same size real image is formed by concave mirror.
86. A concave mirror forms a sharp image of a distant tree. What name is given to the distance between the concave mirror and screen on which sharp image is formed?
Answer/Explanation
Answer:
Explanation: Focal length.
87. In what condition, the image formed by a concave mirror is virtual?
Answer/Explanation
Answer:
Explanation:
When the object is placed between the focus and the pole of a concave mirror, a virtual image is obtained.
88. Specified the size of image formed by a concave mirror when m > 1.
Answer/Explanation
Answer:
Explanation: The image is enlarged.
89. Name the mirror that can be used to check theft in shops.
Answer/Explanation
Answer:
Explanation: Convex mirror.
90. What is the position of the object placed on the side of reflecting surface of a concave mirror of focal length 15 cm if the image is formed at the distance of 30 cm from the mirror?
Answer/Explanation
Answer:
Explanation: 30 cm
91. Which mirror, concave or convex always converges the light rays?
Answer/Explanation
Answer:
Explanation: Concave mirror.
92. For what position of the object does a concave mirror forms a real image which is highly enlarged?
Answer/Explanation
Answer:
Explanation: At F.
93. When object is placed at centre of centre of curvature of concave mirror, where is the image formed?
Answer/Explanation
Answer:
Explanation: At C.
94. What focal length can be assigned to a plane mirror?
Answer/Explanation
Answer:
Explanation: Infinity.
95. Size of the image formed on a concave mirror is highly diminished, state the position of object and image.
Answer/Explanation
Answer:
Explanation:
Position of object: at infinity Position of image : at the focus F
Fill in the Blanks
1. Light shows the phenomena of reflection, refraction and ………. .
2. The speed of light in vacuum is ………. .
3. Power of’ a lens is the ………. of its focal length.
4. The SI unit of power is ………. .
5. A ………. lens will always give a virtual, erect and diminished image, irrespective of the position of the object.
6. A positive sign in the value of magnification indicates that the image is ………. .
7. A ………. mirror is used as a head mirror by the doctors to concentrate light on the body parts to be examined.
8. No matter how far you stand from a spherical mirror, your image appears erect. The mirror may be ………. .
Answers
1. dispersion
2. 3 x 108 m/s
3. reciprocal
4. dioptre
5. concave
6. virtual
7. concave
8. plane or convex mirror .