101: What is the primary source of energy?
Answer: Sun
102: The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
Answer: 10 cm
103: You are given kerosene, turpentine, and water. In which of these does light travel the fastest? (Given: refractive indices of kerosene, turpentine, and water are 1.44, 1.47, and 1.33 respectively)
Answer: Water
104: A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is the same size as the object?
Answer: + 0.5 m
105: Which of the following substances is not used to make lenses?
Answer: Water
106: The resistance of a cylindrical conductor with length l and uniform cross-sectional area A is R. What is the cross-sectional area of the same material with length 2l and resistance R?
Answer: 2A
107: The filament of an electric bulb is made of which element?
Answer: Tungsten
108: An electric bulb is connected to a 220 V generator. The current is 0.5 A. What is the power of the bulb?
Answer: 110 W
109: Which element’s atoms have only two energy levels?
Answer: Magnesium
110: Which of the following mirrors is used by a dentist to examine a small cavity?
Answer: Concave mirror
111: The SI unit of resistivity is
Answer: Ohm per meter
112: The potential difference across the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. If the potential difference is increased to 120 V, how much current will the heater draw?
Answer: 8 A
113: Calculate the total resistance in the circuit. Given: R₁ = 10 Ω, R₂ = 40 Ω, R₃ = 30 Ω, R₄ = 20 Ω, R₅ = 60 Ω, and V = 12 V.
Answer: 25 Ω
114: A student wants to extract energy from fossil fuel. Which process will help her in extracting energy from fossil fuel?
Answer: Combustion
115: How are three resistors of resistances 2Ω, 3Ω, and 6Ω connected to give a total resistance of 4Ω?
Answer: 3Ω and 6Ω resistors are connected in parallel, and this combination is connected in series with the 2Ω resistor.
116: Where should an object be placed in front of a convex lens to obtain a real image of the same size as the object?
Answer: At twice the focal length
117: Which type of mirror is used in a solar furnace?
Answer: Concave
118: An object of length 5 cm is placed at a distance of 25 cm from a converging lens with focal length f. An image is formed at 16.67 cm on the other side of the object. The value of f is:
Answer: +10 cm
119: The far point and near point of the human eye with normal vision are respectively:
Answer: Infinity and 25 cm
120: The focal length of the eye lens changes due to:
Answer: Ciliary muscles