Physics

131. Consider the following physical quantities : Energy, power, pressure,

Consider the following physical quantities :
Energy, power, pressure, impulse, temperature, gravitational potential
Which of the above is / are the vector quantity/quantities ?

[amp_mcq option1=”Impulse only” option2=”Impulse and pressure only” option3=”Impulse, temperature and pressure” option4=”Gravitational potential” correct=”option1″]

This question was previously asked in
UPSC CAPF – 2016
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Among the given physical quantities, only Impulse is a vector quantity. A vector quantity has both magnitude and direction. Impulse is defined as the change in momentum of an object, and momentum (mass × velocity) is a vector quantity. Impulse is also equal to the force multiplied by the time interval over which the force acts (when force is constant), and force is a vector.
Identifying whether a physical quantity is a vector or a scalar is a basic concept in physics.
Energy, power, pressure, temperature, and gravitational potential are all scalar quantities. Scalar quantities are completely described by their magnitude alone. While pressure involves force (a vector) acting over an area (direction can be associated with area normal), pressure itself at a point is a scalar property of the fluid or material. Gravitational potential is potential energy per unit mass, and potential energy is a scalar.

132. Which one of the following statements is not correct ?

Which one of the following statements is not correct ?

[amp_mcq option1=”The rate of evaporation depends on temperature” option2=”The rate of evaporation does not depend on surface area exposed to the atmosphere but on volume of the liquid” option3=”The rate of evaporation depends on humidity of the surroundings” option4=”The rate of evaporation depends on the wind speed” correct=”option2″]

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UPSC CAPF – 2016
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The statement that the rate of evaporation does not depend on surface area exposed to the atmosphere but on volume of the liquid is not correct.
Evaporation is the process where liquid turns into gas below its boiling point. It occurs at the surface of the liquid. The rate of evaporation is influenced by several factors:
A) Temperature: Higher temperature increases the kinetic energy of liquid molecules, making it easier for them to escape the surface. (Correct statement)
B) Surface area exposed: A larger surface area allows more molecules to be at the surface and escape into the atmosphere per unit time, thus increasing the rate of evaporation. Volume of the liquid affects the total amount available for evaporation but not the instantaneous rate of evaporation at a given surface area. (Incorrect statement)
C) Humidity of the surroundings: Lower humidity means the air has a lower concentration of water vapor, creating a larger concentration gradient between the liquid surface and the air, leading to faster evaporation. (Correct statement)
D) Wind speed: Wind blows away the saturated air layer above the liquid surface, replacing it with drier air, which increases the rate of evaporation. (Correct statement)
Evaporation is a crucial part of the water cycle. Other factors influencing evaporation include air pressure and the presence of dissolved substances in the liquid.

133. Water at 273 K is less effective in cooling than ice at the same tempe

Water at 273 K is less effective in cooling than ice at the same temperature. It is because :

[amp_mcq option1=”water is difficult to handle” option2=”water at 273 K has less energy than ice at the same temperature” option3=”water at 273 K has more energy than ice at the same temperature” option4=”water is not a cooling agent” correct=”option3″]

This question was previously asked in
UPSC CAPF – 2016
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Water at 273 K (0°C) is less effective in cooling than ice at the same temperature because water at 273 K has more energy (internal energy) than ice at the same temperature.
When ice at 0°C (273 K) melts into water at 0°C, it absorbs heat from its surroundings. This absorbed heat, known as the latent heat of fusion (approximately 334 kJ/kg for water), is used to break the bonds holding the water molecules in a fixed solid structure and transition to the liquid phase, without causing a change in temperature.
Therefore, water at 0°C possesses this latent heat energy in addition to the energy contained in ice at 0°C.
When ice is used for cooling, it absorbs heat to melt, providing significant cooling due to the latent heat. The resulting water then absorbs further heat as its temperature rises. When water at 0°C is used for cooling, it only absorbs heat as its temperature rises, which provides less cooling capacity compared to the phase change process of ice.
Latent heat is the heat required to change the state of a substance at constant temperature and pressure. Specific heat capacity is the heat required to raise the temperature of a substance by one degree.

134. In a radioactive decay of a nucleus, an electron is also emitted. This

In a radioactive decay of a nucleus, an electron is also emitted. This may happen due to the fact that :

[amp_mcq option1=”electrons are present inside a nucleus” option2=”an electron is created at the time of conversion of a neutron into proton” option3=”an electron is created at the time of conversion of a proton into a neutron” option4=”electrons need to be emitted for conservation of momentum” correct=”option2″]

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UPSC CAPF – 2015
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In radioactive beta minus (β⁻) decay, an electron is emitted because a neutron is converted into a proton within the nucleus.
Beta minus (β⁻) decay is a type of radioactive decay in which a neutron (n) within an atomic nucleus is converted into a proton (p). In this process, an electron (e⁻) and an electron antineutrino (ν̄e) are emitted from the nucleus. The reaction is typically written as: n → p + e⁻ + ν̄e. The electron is not pre-existing within the nucleus; it is created during this transformation. The atomic number of the nucleus increases by one, while the mass number remains unchanged.
Electrons are fundamental particles and are not constituents of the nucleus; protons and neutrons are the nucleons. The electron emitted in beta decay originates from the conversion of a neutron. Another type of beta decay is beta plus (β⁺) decay, where a proton converts into a neutron, emitting a positron (e⁺) and an electron neutrino (νe): p → n + e⁺ + νe. Electron capture is an alternative process where an electron from an inner atomic shell is captured by a proton in the nucleus, leading to the conversion of a proton into a neutron and emission of a neutrino. Momentum and energy conservation rules are followed in all radioactive decay processes, and the emission of the neutrino/antineutrino is necessary for conserving energy, momentum, and angular momentum, but the *reason* for electron emission in β⁻ decay is the fundamental weak interaction process of neutron decay.

135. Two racing cars of masses m₁ and m₂ are moving in circles of radii r₁

Two racing cars of masses m₁ and m₂ are moving in circles of radii r₁ and r₂ respectively. Their speeds are such that each car makes a complete circle in the same time ‘t’. The ratio of angular speed of the first to that of the second car is :

[amp_mcq option1=”m₁ : m₂” option2=”1 : 1″ option3=”r₁ : r₂” option4=”1 : 2″ correct=”option2″]

This question was previously asked in
UPSC CAPF – 2015
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The correct answer is 1 : 1.
Angular speed (ω) is defined as the rate of change of angular displacement. For an object moving in a circle, the angular speed is given by ω = 2π / T, where T is the time period (time taken to complete one revolution). The problem states that both cars make a complete circle in the same time ‘t’. Therefore, the time period T is the same for both cars.
For the first car, ω₁ = 2π / t.
For the second car, ω₂ = 2π / t.
The ratio of their angular speeds is ω₁ : ω₂ = (2π / t) : (2π / t) = 1 : 1.
The masses (m₁ and m₂) and radii (r₁ and r₂) of the cars are irrelevant for determining the ratio of angular speeds when the time period is given to be the same.
Linear speed (v) is related to angular speed and radius by v = rω. If the angular speeds are the same but the radii are different, the linear speeds will be different. Centripetal acceleration (a_c = rω²) and centripetal force (F_c = m a_c = m rω²) would also depend on the mass and radius even if the angular speed is constant. This question specifically asks for the ratio of angular speed, which is determined solely by the time period in this case.

136. γ-ray consists of :

γ-ray consists of :

[amp_mcq option1=”meson particles” option2=”neutrino particles” option3=”Higg’s boson” option4=”electromagnetic waves” correct=”option4″]

This question was previously asked in
UPSC CAPF – 2015
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γ-ray consists of electromagnetic waves. Gamma rays are a form of electromagnetic radiation with the shortest wavelengths and highest frequencies, and therefore highest photon energies. They are part of the electromagnetic spectrum, like visible light or X-rays, but with much higher energy.
Unlike alpha and beta radiation which consist of particles, gamma radiation consists of energy packets (photons) and is an electromagnetic wave.
Gamma rays are typically produced by the decay of atomic nuclei (radioactive decay) or other high-energy processes like electron-positron annihilation. Mesons, neutrinos, and Higgs bosons are types of elementary particles, not constituents of gamma radiation.

137. Movement of outer electrons in the inner orbits of an atom produces :

Movement of outer electrons in the inner orbits of an atom produces :

[amp_mcq option1=”α-ray” option2=”β-ray” option3=”γ-ray” option4=”x-ray” correct=”option4″]

This question was previously asked in
UPSC CAPF – 2015
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Movement of outer electrons in the inner orbits of an atom produces X-rays. When high-energy electrons bombard a target material, they can knock out inner-shell electrons of the target atoms. The vacancies are then filled by electrons from higher energy levels (outer orbits) transitioning to the inner orbits, emitting photons in the process. If the energy difference is large enough, these photons are in the X-ray region of the electromagnetic spectrum.
X-rays are produced when electrons transition between energy levels in the inner shells of atoms or when charged particles are decelerated rapidly (bremsstrahlung). The question specifically refers to electron transitions from outer to inner orbits, which is a mechanism for characteristic X-ray emission.
α-rays are streams of alpha particles (helium nuclei). β-rays are streams of beta particles (electrons or positrons). γ-rays are high-energy electromagnetic waves produced by nuclear transitions. These are fundamentally different from the process described in the question, which relates to electron transitions within the atom’s electron cloud.

138. The radius of a hydrogen atom is 10 -10 m. Number of hydrogen atoms n

The radius of a hydrogen atom is 10-10 m. Number of hydrogen atoms necessary to have a length of one nanometre is :

[amp_mcq option1=”6.023 × 1023” option2=”10″ option3=”5″ option4=”100″ correct=”option3″]

This question was previously asked in
UPSC CAPF – 2015
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The radius of a hydrogen atom is given as 10⁻¹⁰ m. We want to find how many hydrogen atoms are needed to form a length of one nanometre (1 nm). One nanometre is equal to 10⁻⁹ metres. To arrange atoms side-by-side to achieve a certain length, we consider their effective diameter. The diameter of a hydrogen atom is approximately 2 times its radius, i.e., 2 * 10⁻¹⁰ m. The number of atoms needed is the total length divided by the diameter of one atom: Number of atoms = (10⁻⁹ m) / (2 * 10⁻¹⁰ m) = (10⁻⁹ / 10⁻¹⁰) / 2 = 10 / 2 = 5.
When stacking spherical objects (like atoms) linearly, the effective length occupied by each object is its diameter.
The size of atoms is typically on the order of angstroms (1 Å = 10⁻¹⁰ m). A nanometre (1 nm = 10⁻⁹ m = 10 Å) is a unit of length often used in nanoscience and technology. This problem provides a basic illustration of scale conversion between atomic dimensions and nanometre scale.

139. In January 2015, Government of India approved the establishment of a N

In January 2015, Government of India approved the establishment of a Neutrino Observatory at :

[amp_mcq option1=”Bodi hills in Tamil Nadu” option2=”Kaina hills in Manipur” option3=”Jampui hills in Tripura” option4=”Nallamala hills in Andhra Pradesh” correct=”option1″]

This question was previously asked in
UPSC CAPF – 2015
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In January 2015, the Government of India approved the establishment of a Neutrino Observatory at Bodi hills in Tamil Nadu.
The India-based Neutrino Observatory (INO) project received Union Cabinet approval in January 2015 for setting up a mega-science laboratory to study neutrinos. The approved site is in the Bodi West Hills, in the Theni district of Tamil Nadu.
Neutrino observatories are typically located underground to shield the detectors from cosmic rays and other background noise, allowing for the precise detection of neutrinos. The INO project aims to build a large underground detector to study atmospheric neutrinos and potentially solar neutrinos.

140. Which of the following lamps contains a poisonous gas and therefore sh

Which of the following lamps contains a poisonous gas and therefore should be disposed safely ?

[amp_mcq option1=”Compact fluorescent lamp” option2=”Light emitting diode” option3=”Neon lamp” option4=”Halogen lamp” correct=”option1″]

This question was previously asked in
UPSC CAPF – 2014
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Compact fluorescent lamps (CFLs) contain a poisonous substance, mercury vapor.
Compact fluorescent lamps (CFLs) use mercury vapor within a glass tube. When electricity passes through, it excites the mercury vapor, producing ultraviolet (UV) light, which then excites a fluorescent coating on the inside of the tube, causing it to emit visible light. Mercury is a toxic heavy metal that poses environmental and health risks if released, necessitating safe disposal practices for CFLs.
Light-emitting diodes (LEDs) are solid-state devices that do not contain mercury or other hazardous substances found in traditional lighting like CFLs. Neon lamps contain neon gas at low pressure and are generally not considered hazardous in the same way as mercury vapor lamps. Halogen lamps are incandescent lamps containing a halogen gas (like iodine or bromine) within the bulb, which helps extend the filament’s life; they do not typically contain poisonous gases requiring special disposal related to toxicity.
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