2016

171. Arrange the following varieties of silk in India in their order of dec

Arrange the following varieties of silk in India in their order of decreasing production:
1. Muga
2. Eri
3. Mulberry
4. Tasar
Select the correct answer using the code given below

[amp_mcq option1=”3-2-4-1″ option2=”3-4-2-1″ option3=”2-4-1-3″ option4=”2-1-4-3″ correct=”option1″]

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The correct option is A) 3-2-4-1.
Silk production in India involves four main varieties: Mulberry, Eri, Tasar, and Muga. These are categorized based on the type of silkworm that produces the silk fibre. The order of decreasing production volume in India is generally Mulberry, followed by Eri, then Tasar, and finally Muga.
– **Mulberry silk** is the most common type, accounting for the vast majority (around 80-85%) of total silk produced in India. It is produced by the silkworm Bombyx mori, which feeds exclusively on mulberry leaves. It is widely cultivated across various states.
– **Eri silk** is produced by the silkworm Samia cynthia ricini, which feeds mainly on castor leaves. It is primarily concentrated in the North Eastern states, particularly Assam. It is known as the ‘poor man’s silk’ and is also called Ahimsa silk as the moth is allowed to emerge from the cocoon. It accounts for the second-largest production share (around 10-15%).
– **Tasar silk** is produced by silkworms belonging to the Antheraea species, which feed on leaves of trees like Arjun, Asan, and Sal. It is mainly produced in tribal areas of states like Jharkhand, Chhattisgarh, Odisha, West Bengal, etc. Its production share is smaller than Eri (around 5-10%).
– **Muga silk** is produced by the silkworm Antheraea assamensis, which feeds on aromatic leaves of Som and Sualu plants. This silk is unique to Assam and is known for its golden yellow colour and durability. Its production is the lowest among the four varieties due to its localized nature and specific feeding habits of the silkworm.
Thus, the decreasing order of production is Mulberry > Eri > Tasar > Muga.

172. 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″]

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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.

173. 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″]

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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.

174. 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″]

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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.

175. 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″]

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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).

176. 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″]

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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.

177. 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″]

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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).

178. 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″]

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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.

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

Which one of the following statements is not correct ?

[amp_mcq option1=”Graphite is a non-metal” option2=”Graphite is an allotrope of carbon” option3=”Graphite is a conductor of electricity” option4=”Graphite has a tetrahedral structure” correct=”option4″]

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Statement D is incorrect. Graphite has a layered structure where carbon atoms are arranged in hexagonal rings. Each carbon atom is covalently bonded to three other carbon atoms within the same layer. These layers are held together by weak van der Waals forces. A tetrahedral structure is characteristic of diamond, another allotrope of carbon, where each carbon atom is bonded to four other carbon atoms in a three-dimensional network.
Distinguishing between the structures of different allotropes of carbon like graphite and diamond is fundamental in chemistry and materials science.
Statement A is correct: Graphite is an allotrope of carbon, which is a non-metal element.
Statement B is correct: Graphite is one of the naturally occurring allotropes of carbon.
Statement C is correct: Graphite is a good conductor of electricity due to the presence of delocalized electrons within its layered structure, which can move freely along the layers.

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

Which one of the following statements is not correct ?

[amp_mcq option1=”Bleaching powder is prepared by the action of Chlorine on dry slaked lime [Ca(OH)2]” option2=”Bleaching powder acts as a reducing agent in many chemical industries” option3=”Bleaching powder is also known as chlorinated lime” option4=”Bleaching powder is used for disinfecting drinking water” correct=”option2″]

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Statement B is incorrect. Bleaching powder (Calcium oxychloride, CaOCl₂) is a strong oxidizing agent due to the presence of available chlorine. It acts as an oxidizing agent in bleaching processes and disinfection, not a reducing agent. Reducing agents donate electrons or hydrogen atoms, while oxidizing agents accept electrons or remove hydrogen atoms. Bleaching powder facilitates oxidation reactions.
Understanding the chemical properties of common substances like bleaching powder, specifically its role as an oxidizing agent, is important.
Statement A is correct: Bleaching powder is prepared by passing chlorine gas over dry slaked lime [Ca(OH)₂]. The reaction is Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O.
Statement C is correct: Bleaching powder is also known as chlorinated lime or calcium hypochlorite.
Statement D is correct: Bleaching powder is widely used for disinfecting drinking water, swimming pools, and sanitation purposes because its oxidizing action kills bacteria and other microorganisms.
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