UPSC CAPF Archives

11. Which one among the following is not a renewable energy source?

Which one among the following is not a renewable energy source?

Solar

Wind

Nuclear

Hydroelectric

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This question was previously asked in

UPSC CAPF – 2021

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Renewable energy sources are those that are naturally replenished on a human timescale. Non-renewable energy sources are finite and are depleted faster than they can be replenished.

Solar energy, wind energy, and hydroelectric energy are all derived from natural processes that are continuously replenished (sunlight, wind currents, water cycles) and are thus considered renewable. Nuclear energy typically relies on the fission of heavy radioactive elements like uranium or plutonium, which are mined from the Earth and exist in finite quantities. While nuclear fuel sources are substantial, they are not naturally replenished at a rate comparable to their consumption, making nuclear energy generally classified as non-renewable, although it is a low-carbon energy source.

Other renewable energy sources include geothermal energy, biomass energy, and tidal energy. Examples of non-renewable energy sources include fossil fuels (coal, oil, natural gas) and nuclear fuels.

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12. Let an electric current of 1.5 A flow through an incandescent lamp in

Let an electric current of 1.5 A flow through an incandescent lamp in a circuit. What is the amount of charge that flows through it in 10 ms?

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0.015 C

0.15 C

1.5 C

15 C

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UPSC CAPF – 2021

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Electric current (I) is defined as the rate of flow of electric charge (Q) per unit time (t). The relationship is given by Q = I * t.

Given the current (I) = 1.5 A and the time (t) = 10 ms. First, convert the time into seconds: 10 ms = 10 * 10^-3 seconds = 0.01 seconds. Now, calculate the charge: Q = 1.5 A * 0.01 s = 0.015 Coulombs (C).

The unit of electric current is the Ampere (A), and the unit of electric charge is the Coulomb (C). One Ampere is equal to the flow of one Coulomb of charge per second (1 A = 1 C/s). Milliseconds (ms) are a common unit of time, where 1 second = 1000 milliseconds.

13. Which one among the following is not a luminous object?

Which one among the following is not a luminous object?

Sun

Proxima Centauri

Jupiter

Alpha Centauri

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UPSC CAPF – 2021

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Luminous objects are those that produce and emit their own light. Non-luminous objects do not produce light but are visible because they reflect light from a luminous source.

The Sun, Proxima Centauri, and Alpha Centauri are all stars. Stars are massive, luminous celestial bodies that emit light through nuclear fusion. Jupiter is a planet, which is a large celestial body orbiting a star. Planets are non-luminous; they are visible because they reflect the light from their star (in Jupiter’s case, the Sun).

Examples of luminous objects include stars, lamps, and candles. Examples of non-luminous objects include planets, moons, tables, and chairs.

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14. The following figure shows the image of a clock in a plane mirror : [I

The following figure shows the image of a clock in a plane mirror :
[Image of a clock face with hands]
Which one of the following is the correct time?

2:35

3:45

9:15

9:25

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UPSC CAPF – 2021

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A plane mirror produces a laterally inverted image. To find the actual time from a mirror image of a clock, one can imagine flipping the clock face horizontally or subtract the mirror time from 12:00.

Observing the image provided, the minute hand points exactly at the ‘7’, indicating 35 minutes. The hour hand is positioned between ‘2’ and ‘3’, closer to ‘2’. This position of the hour hand, coupled with the minute hand at 7 (35 minutes past the hour), suggests the time shown in the mirror image is 2:35.

If the mirror image shows 2:35, the actual time can be calculated as 12:00 – 2:35. 12:00 is equivalent to 11 hours and 60 minutes. So, (11 hours – 2 hours) and (60 minutes – 35 minutes) gives 9 hours and 25 minutes. Thus, the correct time is 9:25. This matches option D.

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15. When a white light beam is made to fall on a hollow prism filled with

When a white light beam is made to fall on a hollow prism filled with water, it breaks into seven constituent colours. Which of the following colours suffers the maximum angle of deviation?

Red

Violet

Green

All suffer by equal amount of deviation

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UPSC CAPF – 2021

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When a beam of white light passes through a prism, it is dispersed into its seven constituent colours due to the difference in the refractive index of the prism material for different wavelengths of light. The extent to which a colour is deviated depends on the refractive index for that colour; a higher refractive index leads to a greater deviation.

The refractive index of a material is highest for shorter wavelengths (like violet light) and lowest for longer wavelengths (like red light). Consequently, violet light undergoes the maximum deviation, while red light undergoes the minimum deviation.

This phenomenon of splitting white light into its constituent colours is called dispersion. The band of seven colours produced is called the spectrum. The acronym VIBGYOR represents the order of colours in the spectrum from maximum deviation (Violet) to minimum deviation (Red). A hollow prism filled with water still functions as a prism made of water, exhibiting the same dispersion property.

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16. When calcium metal reacts with sulphuric acid, the reaction stops afte

When calcium metal reacts with sulphuric acid, the reaction stops after a short while. Why?

The reaction of calcium with sulphuric acid is not feasible at room temperature

Formed calcium sulphate is insoluble in water and covers the metal, preventing it from reacting any further

Formed calcium sulphate requires two molecules of water to crystallize as gypsum

Formed calcium sulphate is unstable

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UPSC CAPF – 2021

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The correct answer is B) Formed calcium sulphate is insoluble in water and covers the metal, preventing it from reacting any further.

Calcium is a relatively reactive metal that reacts with acids like sulfuric acid to produce hydrogen gas and a salt: Ca(s) + H₂SO₄(aq) → CaSO₄(s) + H₂(g). However, calcium sulfate (CaSO₄) is sparingly soluble in water, and its solubility is even lower in concentrated sulfuric acid. As the reaction proceeds, a layer of solid calcium sulfate forms on the surface of the calcium metal. This layer acts as a barrier, preventing the sulfuric acid from coming into contact with the underlying calcium metal, effectively stopping or significantly slowing down the reaction after a short while. This phenomenon is known as passivation.

Other metals that exhibit passivation with sulfuric acid include lead (forming insoluble PbSO₄) and barium (forming insoluble BaSO₄). With other acids like hydrochloric acid, calcium reacts vigorously because calcium chloride (CaCl₂) is soluble.

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17. Which one of the following metal oxides does not usually react with so

Which one of the following metal oxides does not usually react with sodium hydroxide?

Copper oxide

Aluminium oxide

Potassium oxide

Calcium oxide

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UPSC CAPF – 2021

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The correct answer is A) Copper oxide.

Sodium hydroxide (NaOH) is a strong base. Basic metal oxides react with acids, and acidic oxides react with bases. Amphoteric oxides react with both acids and strong bases.
Aluminium oxide (Al₂O₃) is an amphoteric oxide and reacts with sodium hydroxide: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (at high temperature/concentration) or Al₂O₃ + 6NaOH + 3H₂O → 2Na₃[Al(OH)₆] (in aqueous solution).
Potassium oxide (K₂O) and Calcium oxide (CaO) are basic oxides. They react vigorously with water to form potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)₂), respectively, which are strong bases. Being bases, KOH and Ca(OH)₂ do not react with another base like NaOH.
Copper oxide (CuO) is also a basic oxide. It does not react with water and does not react with sodium hydroxide solution under usual conditions.
Among the given options, Aluminium oxide reacts with NaOH. Potassium oxide and Calcium oxide react with water to form hydroxides that do not react with NaOH. Copper oxide is a basic oxide that neither reacts significantly with water nor with NaOH solution under usual conditions. Therefore, Copper oxide is the one that does not usually react with sodium hydroxide.

Reactivity of metal oxides with bases depends on their acidic, basic, or amphoteric nature. Oxides of highly electropositive metals (Group 1 & 2) are strongly basic. Oxides of transition metals can be basic, amphoteric, or even acidic depending on the oxidation state. Oxides of metalloids and non-metals are typically amphoteric or acidic.

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18. A milkman adds a small amount of baking soda to milk. This makes the p

A milkman adds a small amount of baking soda to milk. This makes the pH of the milk

strongly alkaline

weakly alkaline

strongly acidic

weakly acidic

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UPSC CAPF – 2021

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The correct answer is B) weakly alkaline.

Baking soda is sodium bicarbonate (NaHCO₃), which is a weak base. Milk is slightly acidic or close to neutral, typically having a pH between 6.7 and 6.9. Adding a small amount of a weak base like baking soda to milk will neutralize some of the natural acidity and shift the pH towards the alkaline side. A small amount of a weak base will make the solution weakly alkaline, not strongly alkaline or acidic. Milkmen traditionally added baking soda to milk to prevent it from souring quickly, as it neutralizes the lactic acid produced by bacteria, which causes souring and lowers the pH.

The pH scale measures acidity and alkalinity. A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is alkaline (basic). Adding a base increases the pH.

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19. According to early Indian philosophers, what are the basic elements de

According to early Indian philosophers, what are the basic elements described in Pancha Tattva ?

Earth, Fire, Sky, Gas and Water

Air, Earth, Fire, Sky and Water

Gas, Land, Fire, Sky and Water

Air, Earth, Fire, Land and Water

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The correct answer is B) Air, Earth, Fire, Sky and Water.

According to early Indian philosophical schools (like Samkhya) and traditional Indian medicine systems (like Ayurveda), the universe and everything in it, including the human body, are composed of five basic elements, known as Pancha Mahabhuta or Pancha Tattva. These elements are Prithvi (Earth), Apas (Water), Agni (Fire), Vayu (Air), and Akasha (Sky, Ether, or Space). The terms ‘Gas’ and ‘Land’ in options A, C, and D are not the traditional terms used for these fundamental elements in this philosophical context; ‘Air’ (Vayu) and ‘Earth’ (Prithvi) are the correct traditional terms.

These elements are not understood in the modern chemical sense but represent different states or qualities of matter and energy. Earth represents solidity, Water liquidity, Fire transformation/energy, Air gaseousness/movement, and Sky/Space represents emptiness or the medium in which everything exists.

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20. Packets of potato chips are usually flushed with which one of the foll

Packets of potato chips are usually flushed with which one of the following gases to prevent rancidity?

Carbon dioxide

Hydrogen

Nitrogen

Oxygen

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This question was previously asked in

UPSC CAPF – 2021

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The correct answer is C) Nitrogen.

Packets of potato chips and other similar snacks contain fats and oils. These fats and oils can undergo oxidation when exposed to oxygen in the air, leading to rancidity, which results in unpleasant smells and flavors. To prevent this, the air inside the packets is replaced with an inert gas, most commonly nitrogen. Nitrogen is chosen because it is readily available, inexpensive, and does not react with the food components. This flushing process removes oxygen, significantly slowing down the oxidation process and preventing rancidity, thus extending the shelf life of the product.

This technique is an example of modified atmosphere packaging (MAP), where the gaseous atmosphere surrounding the food is altered to improve preservation. Other gases like carbon dioxide are also sometimes used in food packaging, often in combination with nitrogen.

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