Physics Archives

121. Which one of the following instruments is used for measuring moisture

Which one of the following instruments is used for measuring moisture content of air ?

[amp_mcq option1=”Hydrometer” option2=”Hygrometer” option3=”Hypsometer” option4=”Pycnometer” correct=”option2″]

This question was previously asked in

UPSC CAPF – 2017

A Hygrometer is used for measuring moisture content of air.

– A hygrometer is an instrument used to measure the amount of water vapor in the air, soil, or confined spaces. This is commonly known as humidity.
– A hydrometer is used to measure the specific gravity (or relative density) of liquids, i.e., the ratio of the density of the liquid to the density of water.
– A hypsometer is used to measure elevations or the boiling point of a liquid.
– A pycnometer is a device used to measure the density of solids or liquids.

Different types of hygrometers exist, including mechanical hygrometers, electrical hygrometers (using resistance or capacitance), and dew-point hygrometers. They are essential tools in meteorology, HVAC systems, and various industrial and scientific applications where humidity control is important.

122. Who among the following are awarded with the Special Breakthrough Priz

Who among the following are awarded with the Special Breakthrough Prize in Fundamental Physics for the year 2017 ?

[amp_mcq option1=”Stephen W Hawking and Roger Penrose” option2=”Ronald Drever, Kip S Thorne and Rainer Weiss” option3=”Joseph Polchinski, Andrew Strominger and Cumrun Vafa” option4=”J Michael Kosterlitz, Duncan Haldane and David J Thouless” correct=”option2″]

This question was previously asked in

UPSC CAPF – 2017

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The Special Breakthrough Prize in Fundamental Physics for the year 2017 was awarded to the LIGO scientific collaboration for the observation of gravitational waves. The key individuals representing the collaboration were Ronald Drever, Kip S Thorne, and Rainer Weiss, who were pioneers in the development of the LIGO project.

The prize recognized the detection of gravitational waves, a prediction of Einstein’s general theory of relativity, which opened a new window for observing the universe. Drever, Thorne, and Weiss are considered founding figures of the LIGO experiment.

The 2016 Nobel Prize in Physics was also awarded for this discovery, specifically to Rainer Weiss, Barry C. Barish, and Kip S. Thorne. Ronald Drever had passed away earlier in 2017. The Breakthrough Prize in Fundamental Physics is one of the Breakthrough Prizes founded by Sergey Brin, Priscilla Chan and Mark Zuckerberg, Yuri and Julia Milner, and Anne Wojcicki.

123. Consider the following statements: Statement-I: Occasionally we see

Consider the following statements:

Statement-I: Occasionally we see two rainbows together, the primary rainbow with another less intense secondary rainbow about 10 degrees away
Statement-II: The secondary rainbow appears due to refraction after a reflection of sunlight from the water droplets

Which one of the following is correct in respect of the above statements and the code?

[amp_mcq option1=”Both the statements are individually true and Statement II is the correct explanation of Statement I” option2=”Both the statements are individually true but Statement II is NOT the correct explanation of Statement I” option3=”Statement I is true but Statement II is false” option4=”Statement I is false but Statement II is true” correct=”option3″]

This question was previously asked in

UPSC CAPF – 2017

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Statement I is true; it is possible to see a secondary rainbow outside the primary one. The secondary rainbow is less intense and typically appears about 10 degrees wider than the primary bow, with the colours reversed. Statement II is false; the secondary rainbow is formed by sunlight undergoing *two* internal reflections inside the water droplets before refracting out. The primary rainbow is formed by a single internal reflection.

A secondary rainbow results from two internal reflections of light within raindrops, not one reflection followed by refraction.

The order of colours in the primary rainbow (red on the outside, violet on the inside) is reversed in the secondary rainbow (violet on the outside, red on the inside) due to the extra internal reflection.

124. Which of the following statements is /are correct ? 1. Gravitationa

Which of the following statements is /are correct ?

1. Gravitational Waves were predicted by Albert Einstein in 1916 on the basis of his theory of General Relativity
2. Gravitational waves do also exist in the Newtonian theory of Gravitation
3. Gravitational Waves are to be detected by very sensitive detectors known as Interferometers

Select the correct answer using the code given below :

[amp_mcq option1=”1 only” option2=”1 and 3 only” option3=”2 and 3 only” option4=”1, 2 and 3″ correct=”option2″]

This question was previously asked in

UPSC CAPF – 2016

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Statements 1 and 3 are correct.

1. Albert Einstein predicted the existence of gravitational waves in 1916 as a consequence of his theory of General Relativity. This statement is correct.
2. The Newtonian theory of Gravitation describes gravity as an instantaneous force between masses. It does not predict the existence of gravitational waves which are ripples in spacetime propagating at the speed of light. This statement is incorrect.
3. Gravitational waves are extremely weak and require highly sensitive detectors. Interferometers, such as those used in the LIGO (Laser Interferometer Gravitational-Wave Observatory) and Virgo experiments, are the primary instruments used for their detection. This statement is correct.

The first direct detection of gravitational waves was made by the LIGO collaboration in September 2015 (and announced in February 2016), confirming Einstein’s prediction nearly a century later. This detection originated from the merger of two black holes.

125. Let a resistor having 4 ohm resistance be connected across the termina

Let a resistor having 4 ohm resistance be connected across the terminals of a 12 volt battery. Then the charge in coulomb passing through the resistor per second is:

[amp_mcq option1=”12″ option2=”4″ option3=”3″ option4=”0.33″ correct=”option3″]

This question was previously asked in

UPSC CAPF – 2016

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The correct option is C) 3.

According to Ohm’s Law, the current (I) flowing through a resistor is directly proportional to the voltage (V) across it and inversely proportional to its resistance (R). The relationship is given by the formula V = IR. The current (I) is also defined as the amount of electric charge (Q) passing through a point per unit time (t), i.e., I = Q/t. The question asks for the charge passing through the resistor *per second*, which means we need to find Q when t = 1 second. From I = Q/t, we get Q = I * t. If t = 1 second, then Q = I * 1 = I. Therefore, the charge passing through the resistor per second is equal to the current flowing through it.

Given: Voltage (V) = 12 volts, Resistance (R) = 4 ohm.
Using Ohm’s Law, I = V / R = 12 V / 4 ohm = 3 Amperes.
The current is 3 Amperes, which means 3 Coulombs of charge flow through the resistor every second.
Charge passing per second = Current (I) = 3 Coulombs.

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

Which one of the following statements is not correct?

[amp_mcq option1=”The earth’s magnetic field is due to the motion of metals like iron and nickel in the core of the earth” option2=”The magnetic field lines of force are widely separated near the poles of a magnet but these lines come closer to one another at other places” option3=”If the cross-sectional area of a magnetic field increases, but the flux remains the same, the flux density decreases” option4=”When the speed of a conductor moving through a magnetic field is increased, the induced voltage increases” correct=”option2″]

This question was previously asked in

UPSC CAPF – 2016

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Statement B is incorrect. Magnetic field lines are a visual representation of the magnetic field’s strength and direction. Where the lines are closer together, the magnetic field is stronger; where they are farther apart, the field is weaker. The magnetic field of a bar magnet is strongest at the poles. Therefore, the magnetic field lines of force are most concentrated and come closer to one another near the poles of a magnet, not widely separated. They are more widely separated away from the poles.

Understanding the properties and representation of magnetic field lines is fundamental in magnetism.

Statement A is correct: The Earth’s magnetic field is believed to be generated by the motion of molten metallic materials (primarily iron and nickel) in the Earth’s outer core, a process called the geodynamo.
Statement C is correct: Magnetic flux density (B) is defined as the magnetic flux (Φ) passing through a unit area (A) perpendicular to the direction of the flux (B = Φ/A). If the flux remains constant but the area increases, the flux density decreases.
Statement D is correct: According to Faraday’s law of electromagnetic induction, the magnitude of the induced voltage (EMF) in a conductor moving through a magnetic field is proportional to the speed at which the conductor cuts the magnetic field lines. Thus, if the speed of the conductor is increased, the induced voltage increases.

127. A Barometer kept in an elevator reads 760 mm when the elevator is at r

A Barometer kept in an elevator reads 760 mm when the elevator is at rest. When the elevator moves in the upward direction with increasing speed, the reading of the Barometer will be:

[amp_mcq option1=”760 mm” option2=”< 760 mm" option3="> 760 mm” option4=”Zero” correct=”option3″]

This question was previously asked in

UPSC CAPF – 2016

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When the elevator moves upward with increasing speed (i.e., it is accelerating upwards), the apparent weight of objects inside the elevator increases. A barometer measures the pressure exerted by the column of air above it. In the upward accelerating frame of reference, the effective acceleration of gravity is (g + a), where g is the standard acceleration due to gravity and a is the upward acceleration of the elevator. The pressure exerted by the air column is proportional to this effective gravity. Therefore, the air pressure measured by the barometer will be higher than the normal atmospheric pressure (760 mm Hg) measured when the elevator is at rest.

This question tests the understanding of apparent weight and pressure measurement in accelerating reference frames.

If the elevator were moving downwards with increasing speed (accelerating downwards), the apparent weight and measured pressure would decrease (reading < 760 mm). If the elevator were moving at a constant velocity (up or down), the acceleration would be zero, and the reading would remain 760 mm. If the elevator were falling freely (a = -g), the apparent weight and pressure would be zero.

128. Which one of the following statements is correct ?

Which one of the following statements is correct ?

[amp_mcq option1=”Acceleration due to gravity decreases with the increase of altitude” option2=”Acceleration due to gravity increases with the increase of depth (assuming earth to be a sphere of uniform density)” option3=”Acceleration due to gravity decreases with the increase of latitude” option4=”Acceleration due to gravity is independent of the mass of the earth” correct=”option1″]

This question was previously asked in

UPSC CAPF – 2016

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Statement A is correct. The acceleration due to gravity (g) on the surface of the Earth is given by the formula g = GM/R², where G is the gravitational constant, M is the mass of the Earth, and R is the distance from the center of the Earth. As altitude increases, R increases. Since g is inversely proportional to R², an increase in R leads to a decrease in g.

Understanding how the acceleration due to gravity varies with altitude, depth, latitude, and the mass of the celestial body is essential.

Statement B is incorrect: Acceleration due to gravity decreases with increasing depth inside the Earth. At depth d below the surface, g’ = g(1 – d/R), where R is the radius of the Earth. It becomes zero at the Earth’s center.
Statement C is incorrect: Acceleration due to gravity increases with increasing latitude, from the equator to the poles. This is due to the Earth’s equatorial bulge (closer to the center at poles) and the effect of Earth’s rotation (centrifugal force is maximum at the equator).
Statement D is incorrect: Acceleration due to gravity is directly proportional to the mass of the Earth (M).

129. Which one of the following statements is not true ?

Which one of the following statements is not true ?

[amp_mcq option1=”The gravitational force of earth acting on a body of mass 1 kg is 9.8 newton” option2=”The force acting on an object of mass 5 kg moving with a uniform velocity of 10 m/s on a frictionless surface is zero” option3=”The SI unit of weight is kg” option4=”The momentum of a man having mass 100 kg walking with a uniform velocity of 2 m/s is 200 newton second” correct=”option3″]

This question was previously asked in

UPSC CAPF – 2016

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Statement C is incorrect. Weight is the force exerted on a mass by gravity. The SI unit of force is the Newton (N). Kilogram (kg) is the SI unit of mass, which is a measure of the amount of matter in an object and is independent of gravity. Weight is measured in Newtons.

Distinguishing between mass and weight and knowing their respective SI units is a fundamental concept in physics.

Statement A is correct: The weight of a 1 kg mass on Earth, where the standard acceleration due to gravity (g) is approximately 9.8 m/s², is given by W = mg = 1 kg * 9.8 m/s² = 9.8 N.
Statement B is correct: If an object moves with uniform velocity, its acceleration is zero (a=0). According to Newton’s second law, the net force acting on the object is F = ma. If a=0, then F=0. On a frictionless surface, there are no opposing forces like friction.
Statement D is correct: Momentum (p) is calculated as mass (m) times velocity (v). p = 100 kg * 2 m/s = 200 kg⋅m/s. The unit kg⋅m/s is equivalent to Newton-second (N⋅s), as 1 N = 1 kg⋅m/s². So, the momentum is 200 N⋅s.

130. A piece of stone tied to a string is made to revolve in a circular orb

A piece of stone tied to a string is made to revolve in a circular orbit of radius r with other end of the string as the centre. If the string breaks, the stone will :

[amp_mcq option1=”move away from the centre.” option2=”move towards the centre.” option3=”move along a tangent.” option4=”stop.” correct=”option3″]

This question was previously asked in

UPSC CAPF – 2016

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When an object is revolving in a circular orbit, its velocity at any point is directed tangentially to the circle at that point. The string provides the centripetal force required to keep the object moving in a circular path, constantly changing its direction. If the string breaks, this centripetal force is removed. According to Newton’s first law of motion (the law of inertia), an object in motion will continue in a straight line with constant speed unless acted upon by an external force. Therefore, the stone will move in a straight line along the direction of its instantaneous velocity at the moment the string breaks, which is tangential to the circular orbit.

Understanding inertia and tangential velocity in circular motion is key to predicting the motion of an object when the centripetal force is removed.

This phenomenon demonstrates Newton’s first law and the nature of velocity in circular motion. The stone does not move away from the center (that would imply a radially outward force, which doesn’t exist upon breaking), nor does it move towards the center (as the inward centripetal force is gone), nor does it stop (unless there is friction or air resistance acting).