UPSC CDS-1

21. An antibiotic is not useful against a virus whereas a vaccine is. Whic

An antibiotic is not useful against a virus whereas a vaccine is. Which one of the following is the most appropriate reason for this ?

An antibiotic can break RNA only, whereas virus has DNA.
An antibiotic is a carbohydrate in its chemical nature, whereas a vaccine is a protein which works well to kill a virus.
Only a vaccine can break the genetic material of a virus.
A virus does not use biochemical pathways which can be blocked by an antibiotic. But a vaccine can boost an immune system to fight the virus.
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Antibiotics are designed to kill bacteria by targeting biochemical pathways essential for bacterial life (like cell wall synthesis, protein synthesis, or DNA replication) which are not present or significantly different in host cells. Viruses, however, lack these metabolic pathways and hijack the host cell’s machinery for replication. Therefore, antibiotics are ineffective against viruses. A vaccine, on the other hand, contains weakened or inactivated viruses or viral components (antigens). When administered, it stimulates the host’s immune system to produce antibodies and other immune responses specific to the virus. This prepares the body to fight off the actual virus upon subsequent exposure.
Antibiotics target bacterial processes; viruses lack these processes. Vaccines stimulate the host immune system to recognize and fight specific pathogens like viruses.
The development of antiviral drugs is distinct from antibiotics and targets specific steps in the viral life cycle within host cells.

22. Which one of the following laws of electromagnetism does not give the

Which one of the following laws of electromagnetism does not give the direction of magnetic field ?

Right-hand thumb rule
Fleming's left-hand rule
Fleming's right-hand rule
Faraday's law of electromagnetic induction
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The Right-hand thumb rule gives the direction of the magnetic field produced by a current-carrying wire. Fleming’s Left-hand rule gives the direction of the force acting on a current-carrying conductor placed in a magnetic field (given the directions of current and magnetic field). Fleming’s Right-hand rule gives the direction of the induced current when a conductor moves in a magnetic field (given the directions of motion and magnetic field). Faraday’s law of electromagnetic induction states that a changing magnetic flux through a circuit induces an electromotive force (EMF). While the change in magnetic flux involves the magnetic field, Faraday’s law primarily quantifies the magnitude of the induced EMF and does not directly provide a rule for determining the direction of the magnetic field itself. (Lenz’s law, often used alongside Faraday’s law, provides the direction of the induced current/EMF, opposing the change in flux).
Faraday’s Law quantifies the magnitude of induced EMF due to changing magnetic flux; the other rules/laws listed are primarily used to determine directions related to magnetic fields, current, force, or motion.
Right-hand rules and Fleming’s rules are mnemonic tools for remembering the vector relationships in electromagnetism. Faraday’s law is a fundamental principle linking changing magnetic fields to induced electrical effects.

23. Who amongst the following is a pioneer in discovering the heating effe

Who amongst the following is a pioneer in discovering the heating effect of electric current ?

Isaac Newton
Galileo Galilei
James P. Joule
J.J. Thomson
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James Prescott Joule was a physicist who studied the nature of heat and its relationship to mechanical work. He is best known for establishing that electric current produces heat when it flows through a resistance, quantifying this effect in what is now known as Joule’s law of heating, which states that the heat produced is proportional to the square of the current, the resistance, and the time ($H \propto I^2Rt$).
James P. Joule’s experiments demonstrated the relationship between electric current flow through a resistor and the heat generated, leading to Joule’s Law of Heating.
Isaac Newton formulated laws of motion and universal gravitation. Galileo Galilei made significant contributions to astronomy and the study of motion. J.J. Thomson discovered the electron.

24. A non-spherical shining spoon can generally be considered as a

A non-spherical shining spoon can generally be considered as a

Spherical mirror
Parabolic mirror
Plane mirror
Lens
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A shining spoon has a curved surface that acts as a mirror. While the inner part acts like a concave mirror and the outer part like a convex mirror, the curve of a spoon is generally not a perfect sphere. A common non-spherical curved mirror shape is a parabolic mirror, which has the property of focusing parallel light rays to a single point. Given that the spoon is described as ‘non-spherical’, a parabolic mirror is a suitable description for a curved mirror that is not spherical. It is definitely not a plane mirror or a lens.
A spoon’s curved, reflective surface acts as a mirror. Non-spherical curved mirrors, like parabolic mirrors, have specific shapes and optical properties.
Spherical mirrors are simpler approximations often used in basic optics. Parabolic mirrors are used in applications requiring precise focusing, such as telescopes and satellite dishes.

25. Which one of the following is an electric conductor ?

Which one of the following is an electric conductor ?

A plastic sheet
Distilled water
Human body
A wooden thin sheet
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An electric conductor is a material that allows electric current to flow through it easily. Plastic and wood are electrical insulators, meaning they resist the flow of electricity. Distilled water is a very poor conductor of electricity because it contains very few ions. The human body contains various salts dissolved in water, which provide ions that can carry electric charge, making the human body a conductor of electricity.
Conductors allow charge flow, insulators resist it. The presence of free charge carriers (like ions in solutions or free electrons in metals) determines conductivity.
Metals like copper and aluminum are excellent conductors. Pure water is a poor conductor; its conductivity increases significantly with dissolved impurities (salts, acids, bases) that form ions.

26. Which of the following statements about ‘fission’ is correct ? 1. It

Which of the following statements about ‘fission’ is correct ?

  • 1. It is related with the creation of new individuals by means of cell division in unicellular organism.
  • 2. It is related with the transformation of heavier nuclei into smaller nuclei.
  • 3. It is related with the creation of a heavier nuclei by means of combining two higher nuclei.

Select the correct answer using the code given below :

1 only
2 only
1 and 2 only
1 and 3 only
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Statement 1 is correct as fission in biology refers to cell division for reproduction in unicellular organisms like bacteria and amoeba, resulting in the creation of new individuals. Statement 2 is correct as nuclear fission is a process in nuclear physics where a heavy atomic nucleus splits into smaller, lighter nuclei, often releasing energy. Statement 3 describes nuclear fusion, where lighter nuclei combine to form a heavier nucleus, which is the opposite of nuclear fission. Therefore, statements 1 and 2 correctly describe different types of ‘fission’.
Fission refers to splitting or division, occurring in both biological (cell division) and nuclear (heavy nucleus splitting) contexts. Fusion is the combining of nuclei.
Binary fission is the most common form of reproduction in prokaryotes. Nuclear fission is used in nuclear power plants and atomic bombs. Nuclear fusion occurs naturally in stars.

27. We are given three copper wires of different lengths and different are

We are given three copper wires of different lengths and different areas of cross-section. Which one of the following would have highest resistivity ?

Copper wire of 50 cm length and 1 mm diameter
Copper wire of 25 cm length and 0.5 mm diameter
Copper wire of 10 cm length and 2.0 mm diameter
All the wires would have same resistivity
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Resistivity is a fundamental property of a material that describes its resistance to electrical conduction. It depends only on the nature of the material and its temperature, not on its dimensions (length or area of cross-section).
– The resistance (R) of a wire is given by the formula R = ρ * (L/A), where ρ is the resistivity, L is the length, and A is the area of cross-section.
– While the resistance (R) of the copper wires will be different because they have different lengths and diameters, their resistivity (ρ) will be the same because they are all made of the same material (copper) and are presumably at the same temperature.
– Resistance is an extrinsic property that depends on both the material’s resistivity and its physical dimensions.
– Resistivity is an intrinsic property specific to the material itself.

28. Which one of the following metals has both malleability and ductility

Which one of the following metals has both malleability and ductility properties ?

Na
Au
Ce
Hg
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Gold (Au) is a well-known metal that exhibits both malleability and ductility to a very high degree. It can be hammered into extremely thin sheets (gold leaf) and drawn into very fine wires.
– Malleability is the ability of a material to be deformed under compression without fracturing (hammered into sheets).
– Ductility is the ability of a material to be deformed under tensile stress without fracturing (drawn into wires).
– These properties are characteristic of metals due to the nature of metallic bonding.
– Sodium (Na) is malleable and ductile but much softer and less durable than gold.
– Cerium (Ce) is a malleable metal, but not as famously malleable and ductile as gold.
– Mercury (Hg) is a liquid at room temperature and therefore does not exhibit these solid-state mechanical properties.
– Gold is considered the most malleable and ductile of all metals.

29. Which one of the following elements is a non-metal but is lustrous ?

Which one of the following elements is a non-metal but is lustrous ?

Carbon
Silicon
Germanium
Iodine
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Iodine is a halogen (Group 17 element) and is classified as a non-metal. However, solid iodine crystals have a distinct metallic lustre (shiny appearance), making it an exception to the general rule that non-metals are non-lustrous.
– Metals are typically lustrous, malleable, ductile, and good conductors of heat and electricity.
– Non-metals are typically brittle, non-lustrous, and poor conductors (except for graphite).
– Iodine exhibits properties characteristic of non-metals (e.g., it forms negative ions, is a poor conductor of electricity in solid form) but stands out for its metallic lustre in solid state.
– Carbon exists in various allotropes; diamond is very lustrous, and graphite has a dull metallic sheen, but elemental carbon is broadly considered a non-metal.
– Silicon and Germanium are metalloids, possessing properties intermediate between metals and non-metals, and they are typically lustrous semiconductors. The question asks for a non-metal.

30. A solution contains 20 g of solute in 180 g of solvent. If the solvent

A solution contains 20 g of solute in 180 g of solvent. If the solvent is water, what is the concentration of the solution in terms of mass percentage ?

11·1%
22·2%
10%
20%
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The concentration of a solution in terms of mass percentage is calculated as (Mass of solute / Mass of solution) × 100%.
– Mass of solute = 20 g
– Mass of solvent = 180 g
– Mass of solution = Mass of solute + Mass of solvent = 20 g + 180 g = 200 g
– Mass percentage = (20 g / 200 g) × 100% = (1/10) × 100% = 10%.
– Mass percentage is a common way to express concentration and is useful when dealing with mixtures of solids or liquids.
– Other concentration units include molarity, molality, volume percentage, etc.
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