Polytechnic Physics Set 7

121: Which of the following is not attracted by a magnet?

Steel Cobalt Brass Nickel

Answer: Brass

122: When a straight conductor carries an electric current,

Circular magnetic field lines surround it Magnetic field lines are parallel to the conductor There are no magnetic field lines None of the above

Answer: Circular magnetic field lines surround it

123: Why is biogas considered a good source of energy?

Because it produces ash Because it produces methane Because it burns smoke-free Because it decomposes in the absence of oxygen

Answer: Because it produces methane

124: Rehan can use any energy source for cooking, but he wants to avoid smoke production from the source. Which of the following sources should he use for cooking?

Coal Wood Petroleum Electricity

Answer: Electricity

125: Which of the following processes explains the harnessing of solar energy to produce electricity for lighting a bulb?

Conversion of electrical energy to solar energy Conversion of solar energy to electrical energy Conversion of solar energy to kinetic energy Conversion of kinetic energy to solar energy

Answer: Conversion of solar energy to electrical energy

126: If the power of a lens is -2D, what is its focal length?

+50 cm -100 cm -50 cm +100 cm

Answer: -100 cm

127: The black open part between the cornea and the lens is called

Retina Iris Cornea Pupil

Answer: Pupil

128: A rectangular coil of copper wire is rotated in a magnetic field. How many times does the direction of induced current change in each rotation?

Two rotations One rotation Quarter rotation Half rotation

Answer: Two rotations

129: The sun appears white at noon because

There is minimum scattering of light All colors of white light are scattered Blue color is scattered the most Red color is scattered the most

Answer: All colors of white light are scattered

130: A wire with resistivity and length l is cut into two equal parts. The resistivity of each part is

4ρ ρ/2 2ρ ρ

Answer: 2ρ

131: An object is placed 0.25 m in front of a plane mirror. The distance between the object and the image will be

0.25 m 1.0 m 0.125 m 0.5 m

Answer: 1.0 m

132: The angle of incidence for a light ray with zero reflection angle is

0° 30° 45° 90°

Answer: 0°

133: The nature of the image formed by a convex mirror when the object distance from the mirror is less than the distance between the pole and the focal point (F) will be

Real, inverted, and smaller in size Real, inverted, and larger in size Virtual, upright, and smaller in size Virtual, upright, and larger in size

Answer: Virtual, upright, and larger in size

134: The refractive index of water is 1.33. The speed of light in water is (given speed of light in vacuum = 3 x 10⁸ m/s)

1.33 x 10⁸ m/s 3 x 10⁸ m/s 2.26 x 10⁸ m/s 2.66 x 10⁸ m/s

Answer: 2.26 x 10⁸ m/s

135: The magnification of a concave lens is

Always > 1 Always < 1 Always = 1 Can be any value

Answer: Always < 1

136: The device used to detect electric current in a circuit is called

Electric Motor AC Generator Galvanometer None of the above

Answer: Galvanometer

137: An AC generator works on the principle of

Force experienced by a conductor in a magnetic field Electromagnetic Induction Electrostatics Force experienced by a charged particle

Answer: Electromagnetic Induction

138: Fossil fuels are

Non-renewable sources of energy Renewable sources of energy Both (A) and (B) Neither (A) nor (B)

Answer: Non-renewable sources of energy

139: 1 kilowatt-hour =

3.6 x 10⁶ Joules 3.6 x 10² Joules 3.6 Joules 3.6 x 10¹⁰ Joules

Answer: 3.6 x 10⁶ Joules

140: A hydroelectric power plant is located in

Desert region Hilly region Plains None of the above

Answer: Hilly region