UPSC NDA-2

11. Cornea in human eye

Cornea in human eye

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is a light sensitive screen.
is a muscular diaphragm.
contains blood vessels.
is composed of proteins and cells.
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The correct answer is D) is composed of proteins and cells.
The cornea is the transparent outer layer at the front of the eye. It is composed of highly organized layers of collagen proteins and specialized cells, which contribute to its transparency and structural integrity.
The retina (A) is the light-sensitive screen at the back of the eye. The iris (B) is a muscular diaphragm that controls the size of the pupil. The cornea (C) is avascular, meaning it does not contain blood vessels, which is crucial for its transparency.

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12. Twinkling of stars is primarily due to the atmospheric

Twinkling of stars is primarily due to the atmospheric

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refraction
reflection
polarization
dispersion
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The correct answer is A) refraction.
Twinkling of stars is caused by atmospheric refraction. As starlight passes through different layers of the Earth’s atmosphere with varying densities and temperatures, it undergoes repeated refraction in random directions, causing the apparent position and brightness of the star to fluctuate.
Planets, being much closer than stars, appear as extended sources rather than point sources. The total amount of light entering the eye from a planet remains relatively constant despite atmospheric refraction, which is why planets do not appear to twinkle.

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13. Tyndall effect is a phenomenon of

Tyndall effect is a phenomenon of

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scattering of light by the colloidal particles.
refraction of light by the colloidal particles.
dispersion of light by dust particles.
refraction of light by dust particles.
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The correct answer is A) scattering of light by the colloidal particles.
The Tyndall effect is the scattering of light as a light beam passes through a colloid. The individual suspension particles scatter and reflect light, making the beam visible.
This phenomenon is exhibited by colloidal solutions and fine suspensions, but not by true solutions. It is used to distinguish between a true solution and a colloidal solution. While dust particles can also scatter light, the term Tyndall effect is specifically associated with scattering by colloidal particles.

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14. Myopia is a defect in human vision where an image of a

Myopia is a defect in human vision where an image of a

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nearby object is focused beyond the retina.
nearby object is focused before the retina.
distant object is focused before the retina.
distant object is focused beyond the retina.
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The correct answer is C) distant object is focused before the retina.
Myopia, or nearsightedness, is a refractive error where light from distant objects is focused in front of the retina instead of directly on it. This results in distant objects appearing blurred.
In myopia, nearby objects are typically focused correctly on the retina (or even slightly behind, requiring less accommodation effort compared to a normal eye), which is why nearby vision is usually clear. Hyperopia (farsightedness) is when light is focused behind the retina.

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15. The device used to produce electric current is known as

The device used to produce electric current is known as

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motor
generator
ammeter
galvanometer
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The correct answer is B) generator.
A generator is a device that converts mechanical energy into electrical energy, thereby producing electric current.
A motor converts electrical energy into mechanical energy. An ammeter is used to measure electric current. A galvanometer is used to detect or measure small electric currents.

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16. Imagine a current-carrying straight conductor with magnetic field of l

Imagine a current-carrying straight conductor with magnetic field of lines in anti-clockwise direction. Then the direction of current is determined by

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the Right-Hand Thumb rule and it would be in the downward direction.
the Left-Hand Thumb rule and it would be in the downward direction.
the Right-Hand Thumb rule and it would be in the upward direction.
the Left-Hand Thumb rule and it would be in the upward direction.
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The direction of the magnetic field around a straight current-carrying conductor is determined by the Right-Hand Thumb Rule (also known as Ampere’s Right-Hand Rule). According to this rule, if you point the thumb of your right hand in the direction of the conventional current, your fingers curl in the direction of the magnetic field lines around the wire. The question states the magnetic field lines are in an anti-clockwise direction when viewed from a certain perspective (presumably from above the conductor). If the current were downwards, using the right-hand rule, your fingers would curl clockwise. If the current were upwards, your fingers would curl anti-clockwise. Since the magnetic field is anti-clockwise, the current must be in the upward direction, and the rule used is the Right-Hand Thumb rule.
The Right-Hand Thumb Rule for a straight conductor states: Point your right thumb in the direction of the conventional current. Your fingers curl in the direction of the magnetic field. An anti-clockwise magnetic field (when looking down onto the wire) implies the current is flowing upwards.
The Left-Hand Rule is typically used in contexts involving forces on current-carrying conductors in magnetic fields (Fleming’s Left-Hand Rule) or for the direction of force on a moving charge in a magnetic field. For determining the direction of the magnetic field created by a current, the Right-Hand Rule is used.

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17. Cinnabar is an ore of which one of the following ?

Cinnabar is an ore of which one of the following ?

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Copper
Zinc
Mercury
Manganese
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Cinnabar is a mineral that is the chief ore of mercury. Its chemical composition is mercury(II) sulfide (HgS). It is known for its distinctive bright red color and is historically important as a source of mercury metal.
Cinnabar is the main ore from which mercury (Hg) is extracted. It is chemically represented as HgS.
Copper ores include chalcopyrite ($\text{CuFeS}_2$) and malachite ($\text{Cu}_2\text{CO}_3(\text{OH})_2$). Zinc ores include sphalerite (ZnS) and calamine (a historical term for zinc ores, including smithsonite ($\text{ZnCO}_3$) and hemimorphite ($\text{Zn}_4\text{Si}_2\text{O}_7(\text{OH})_2 \cdot \text{H}_2\text{O}$)). Manganese ores include pyrolusite ($\text{MnO}_2$).

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18. To protect steel and iron from rusting, a thin layer of which one of t

To protect steel and iron from rusting, a thin layer of which one of the following metals is applied ?

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Magnesium
Zinc
Aluminium
Lead
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Rusting is the process of oxidation of iron, forming hydrated iron(III) oxide. To protect iron and steel from rusting, a protective layer of another metal is applied. Zinc is commonly used for this purpose through a process called galvanization. Zinc is more reactive than iron, and it preferentially corrodes, acting as a sacrificial layer to protect the underlying iron or steel even if the coating is scratched.
Galvanization, the process of coating iron or steel with a thin layer of zinc, is a widely used method to prevent rusting. Zinc acts as a barrier and also provides sacrificial protection (cathodic protection) because it is more electrochemically active than iron.
Other methods to prevent rusting include painting, oiling, greasing, chrome plating, tin plating, and alloying (like making stainless steel). Aluminium is also more reactive than iron and forms a protective oxide layer, but galvanization with zinc is the most common method among the options listed for general anti-rust protection of steel and iron.

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19. Which one of the following elements’ isotopes is used in the treatment

Which one of the following elements’ isotopes is used in the treatment of cancer ?

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Iodine
Sodium
Cobalt
Uranium
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Radioactive isotopes are used in medicine for diagnosis and treatment. In the treatment of cancer, a process called radiotherapy is often used, which involves using radiation to kill cancer cells. Cobalt-60 is a radioactive isotope that emits high-energy gamma rays. These gamma rays can penetrate tissue and are used in external beam radiotherapy machines (often called “Cobalt therapy”) to target and destroy cancerous tumors.
Cobalt-60 ($^{60}$Co) is a common radioactive isotope used in cancer treatment (radiotherapy) due to its emission of gamma rays. While Iodine-131 is used to treat thyroid cancer, Cobalt-60 is used for a broader range of cancers in external radiotherapy.
Other radioisotopes used in medicine include Iodine-131 (thyroid conditions), Technetium-99m (diagnostic imaging), and Iridium-192 (brachytherapy). Uranium isotopes are mainly used as nuclear fuel and in nuclear weapons, not typically in medical treatment.

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20. Chlorine occurs in nature in two isotopic forms of masses 35 u and 37

Chlorine occurs in nature in two isotopic forms of masses 35 u and 37 u in the ratio of 3 : 1 respectively. What is the average atomic mass of the Chlorine atom ?

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36·1 u
35·5 u
36·5 u
35·1 u
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Chlorine exists as two isotopes: $^{35}$Cl with a mass of 35 u and $^{37}$Cl with a mass of 37 u. They are present in nature in a ratio of 3:1. This means that out of every 4 chlorine atoms, approximately 3 have a mass of 35 u and 1 has a mass of 37 u. The average atomic mass is calculated as a weighted average of the masses of the isotopes based on their relative abundance. The relative abundance of $^{35}$Cl is 3/4 or 0.75, and the relative abundance of $^{37}$Cl is 1/4 or 0.25.
Average atomic mass = ($\text{Mass of isotope 1} \times \text{Fractional abundance of isotope 1}$) + ($\text{Mass of isotope 2} \times \text{Fractional abundance of isotope 2}$)
Average atomic mass = $(35 \text{ u} \times 3/4) + (37 \text{ u} \times 1/4)$
Average atomic mass = $(105/4) \text{ u} + (37/4) \text{ u}$
Average atomic mass = $(105 + 37)/4 \text{ u}$
Average atomic mass = $142/4 \text{ u}$
Average atomic mass = $35.5 \text{ u}$.
Atomic mass unit (u) is a standard unit used for indicating atomic and molecular masses. Average atomic mass is the value listed for an element on the periodic table. It reflects the natural isotopic composition of the element.

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