SOLVED PAPER 2021 (CDS) (II) (General Studies)

Total Questions: 120

101. Where should an object be placed in front of a convex lens to get a real and enlarged image of the object?

Correct Answer: (c) Between the principal focus and twice the focal length
Solution:

To form an inverted and enlarged image by a convex lens, the object should be placed between F and 2F in front of the lens i.e. Between the principal focus and twice the focal length.

102. The magnetic field lines inside a current carrying long solenoid are in the form of

Correct Answer: (d) parallel straight lines
Solution:

One end of the solenoid behaves as a magnetic North pole, while the other behaves as the South pole. The field lines inside the solenoid are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid. That is, the field is uniform inside the solenoid.

103. A ray of light travelling from a rarer medium to a denser medium

Correct Answer: (b) slows down and bends towards the normal.
Solution:

When a ray of light enters from a rarer to denser medium, light bends towards the normal and slows down. Since the speed of light changes as it enters from a rarer to denser medium the frequency of light does not change but its wavelength changes.

104. An electric circuit is consisting of a cell, an ammeter and a nichrome wire of length l. If the length of the wire is reduced to half (l/2), then the ammeter reading

Correct Answer: (b) gets doubled
Solution:

105. What is the effect of pressure of a human body on sand?

Correct Answer: (a) Larger while standing than while lying.
Solution:

The effect of pressure of a human body on sand is larger while standing than while lying because the pressure exerted on a surface by an object increases as the weight of the object increases or the surface area of contact decreases. Alternatively the pressure exerted decreases as the weight of the object decreases or the surface area of contact increases.

106. An athlete completes one round of a circular track of diameter 100 m in 20 s. What will be the displacements after 1 minute and 10 s, respectively?

Correct Answer: (a) 0 m, 50 m
Solution:

Displacement = Final position – initial position = change in position. After 1 minutes i.e. 60 sec, Displacement will be 0 m as change in position will be 0 m because athlete will be at the Initial position. After 10 s , Displacement will be 50 m (50 - 0) is the change on position of the athlete.

107. Which of the following statements about universal indicator is/are true?

1. It is a mixture of several indicators.
2. It shows different colours at different concentrations of hydrogen ions in solution.
3. It helps to determine the strength of given acid and base in titration.

Select the correct using the codes given below.

Correct Answer: (d) 1,2 and 3
Solution:

Statements 1,2 and 3 are correct. A universal indicator is a pH indicator made of a solution of several compounds that exhibits several smooth colour changes over a wide range pH values to indicate the acidity or alkalinity of solutions. The main components of a universal indicator, in the form of a solution, are thymol blue, methyl red, bromothymol blue and phenolphthalein. This mixture is important because each component loses or gains protons depending upon the acidity or alkalinity of the solution being tested.

108. Which of the following carbon allotropes is/are good conductor(s) of electricity?

1. Diamond
2. Graphite
3. Fullerene

Select the correct using the codes given below.

Correct Answer: (c) Only 2
Solution:

Graphite is a good conductor of electricity because in a graphite molecule, one valence electron of each carbon atom remains free. Due to the free electrons in its framework, graphite can perform electricity. Therefore, graphite is said to be a good conductor of electricity.

109. What is the approximate percentage of carbon in the Earth’s crust?

Correct Answer: (b) 0.025%
Solution:

Although widely distributed in nature, carbon is not particularly plentiful as it makes up only about 0.025 per cent of Earth’s crust yet it forms more compounds than all the other elements combined. Carbon is a chemical element with the symbol C and atomic number is 6. It is non-metallic and tetravalent element. It is having 4 electrons available for covalent chemical bonds. It belongs to group 14 of the periodic table.

110. When copper reacts with moist carbon dioxide (CO₂) in air, it forms a green coating of which one of the following compounds?

Correct Answer: (a) Cupric carbonate
Solution:

Cupric carbonate, Cu₂ (OH)₂ CO₃ , is formed when copper(Cu) reacts with moist carbon dioxide (CO₂ ) in air. Cupric Carbonate is used as a pigment in products, paints and varnishes. Copper carbonate is used in artist paints to obtain desired colours for which it is also known with different names such as verditer and mountain green. Copper carbonate is highly demanded in fireworks and pottery glazes as pigment and colorant.