# “The Knowledge Library”

#### Knowledge for All, without Barriers…

##### An Initiative by: Kausik Chakraborty.
12/12/2023 1:41 AM

# “The Knowledge Library”

Knowledge for All, without Barriers……….

# The Knowledge Library

1.A cardboard is placed on a glass of water, and a ten-paise coin is placed on the cardboard. If the cardboard is flicked suddenly in the direction parallel to its surface, then the cardboard flies away, but the coin falls in the glass.
The behaviour of the coin can be explained by which among the following properties?

[A] Momentum
[B] Acceleration
[C] Inertia
[D] Friction

Notes:
Inertia is the property of matter that is why it continues in its existing state of either rest or motion. It can be changed by an external force. Here in the question the coin falls in the glass even after the cardboard is flicked because it maintains its rest position by the nature of inertia.

2.A Pendulum Clock, whose pendulum is made up of a steel rod, will become slow if __:
1. Temperature rises
2. Taken to moon
3. Taken from equator to pole
Choose the correct option from the codes given below:

[A] Only 1
[B] Only 1 & 2
[C] Only 2 & 3
[D] 1, 2 & 3

Correct Answer: B [ Only 1 & 2]

Notes:
The length of the pendulum increases if temperature increases and the time period T increases and a pendulum takes more time to complete one oscillation. That is why it becomes slow. As the moon’s gravity of about 1/6 of Earth’s gravity, and period of a pendulum increases with a decrease in gravity so it will take more time to complete one oscillation. When a pendulum is taken from the equator to the pole, gravity increases, Time period decreases and it will start oscillating faster.

[A] It is an ionizing radiation
[B] It is unable to penetrate human skin
[C] It is toxic to human tissues
[D] It is not cost effective

Correct Answer: B [ It is unable to penetrate human skin]

Notes:
The alpha particles have very large atomic volume and hence do not penetrate human skin.

4.Which among the following cease to exist (or become zero) at Absolute zero temperature on Kelvin scale?
1. Oscillation of the atoms and molecules
2. Entropy
3. Electrical resistance
Choose the correct option from the codes given below:

[A] Only 1
[B] Only 1 & 2
[C] Only 2 & 3
[D] None of them

Correct Answer: D [ None of them]

Notes:
Oscillation of the atoms and molecules, Entropy, Electrical resistance none of them cease to exist at Absolute zero temperature on Kelvin scale.

5.What is / are the objectives of using tubeless tyres in the aircrafts?
1. To reduce chances of detatching the tyre from the rim
2. To make them withstand shocks better
3. To allow them withstand heat Select the correct option from the codes given below:

[A] Only 1 & 2
[B] Only 2 & 3
[C] Only 1 & 3
[D] 1, 2 & 3

Correct Answer: D [ 1, 2 & 3]

Notes:
The aircraft tyre needs to accelerate from standstill to a high speed instantaneously and may have a significant crosswind offset load, so there’s a high probability of detatching the tyre from the rim. Further, there are several advantages of tubeless tyres as follows:

• Maintenance of air pressure
• Puncture proof
• They can withstand shocks etc better
• Heat is produced during landing. As there is no tube, there is no possibility of the tube stretching
• An air-retaining lining is provided between tyre and steel rim which does not have spokes or holes.

6.If the frequency of a sound wave is reduced to half of its original value, then the speed of sound wave will:
[A] reduce to half of its original value
[B] double to that of its original value
[C] increase fourfold of its original value
[D] remain same

Correct Answer: A [ reduce to half of its original value]

Notes:
The frequency and wavelength formulas of sound waves is given as follows:
. In the above, Greek letter lambda λ is the symbol for wavelength.

7.On heating a pure silicon circular disc with a circular hole at the centre, the diameter of the hole:

[A] will expand
[B] will contract
[C] will remain constant
[D] may expand or contract

Correct Answer: B [ will contract]

Notes:
Pure silicon has a negative coefficient of thermal expansion for temperatures and hence it shows contraction effect.

8.In recent times, the Optical fibres have become popular for usage in data transmissions. What advantages is / are offered by the Optical Fibres?

1. Transmission via optical fibres is immune to electromagnetic interference
2. Optical fibres can transmit data at a faster speed in comparison to metals

Select the correct option from the codes given below:

[A] Only 1
[B] Only 2
[C] Both 1 & 2
[D] Neither 1 nor 2

Correct Answer: C [ Both 1 & 2]

Notes:
The difference between a fibre optic communication system and other types of communication is that signals are transmitted as light in optic communication. Conventional electronic communication relies on electrons passing through wires. Since fibres transmit signals as light rather than current (as in other cables), they are immune to electromagnetic interference which causes noisy data transmission in wires. Because of this, they are used where data security is critical. As no shielding is required against electromagnetic interference, they are smaller and more flexible, which makes installation much easier than metal cables. Fibre optic cable is more efficient than other cables as it has lower attenuation, mainly because light is not radiated out in the way that electricity is radiated from copper cables. Non-conductive nature of fibres avoid spark hazards and damage to electronic equipment from power surges. They can transmit signals at higher speeds or over long distances. Copper wires are adequate for the vast bulk of computer data transmission over point to point links and local area networks. They react differently to tension as they are elastic and copper is inelastic. Optical fibres can be used to sense, illuminate, deliver laser power, display and image as well as to communicate. One disadvantage is that they are more expensive than other cables.

9.Which of the following is not a valid conservation law of classical Physics?

[A] Law of conservation of energy
[B] Law of conservation of current
[C] Law of conservation of angular momentum
[D] Law of conservation of charge

Correct Answer: B [Law of conservation of current]

Notes:
The following laws are dealt with in the classical physics: 1. Law of conservation of energy 2. Law of conservation of angular momentum 3. Law of conservation of linear momentum 4. Law of conservation of charge

10.Electron microscope works on which of the following principles?

[A] Optical interference
[B] Wave Nature of electrons
[C] Motion of charged particle in electromagnetic fields
[D] Faraday’s law of Electromagnetic induction

Correct Answer: B [Wave Nature of electrons]

Notes:
Electron microscope works on the principle of Wave Nature of electrons. Electron microscopes use an electron beam instead of visible light and an electron detector instead of our eyes. An electron beam allows us to see at very small scales because electrons can also behave as light due to its wave nature.

11.What is the slope of the velocity-time graph when an object moves with constant negative acceleration, having positive initial velocity?

[A] 90°
[B] more than 90°
[C] less than 90°
[D] 0°

Correct Answer: B [more than 90°]

Notes:
When an object moves with constant negative acceleration, having positive initial velocity, the velocity-time graph is a straight line having slope more than 90°. When an object moves with constant positive acceleration, having positive initial velocity, the velocity-time graph is a straight line having slope less than 90°.

12.The motion of an object under free fall is an example of which of the following?

[A] uniform velocity
[B] uniform acceleration
[C] zero acceleration
[D] non-uniform acceleration

Notes:
The motion of an object under free fall is a case of uniform acceleration. If an object is released from a height near the surface of earth, it accelerates downwards under the influence of a gravity pull with acceleration due to gravity.

13.What is the angular acceleration of a body moving with constant angular velocity?

[A] equal to the angular velocity
[B] 1
[C] 0
[D] Can’t be determined

Notes:
The angular acceleration of a body moving with constant angular velocity is 0. Angular acceleration of an object in circular motion is defined as the time rate of change of its angular velocity.

14.What is the maximum height that can be attained by a projectile?

[A] equal to its maximum range
[B] one half of its maximum range
[C] one-fourth of its maximum range
[D] twice of its maximum range

Correct Answer: C [one-fourth of its maximum range]

Notes:
The maximum height that can be attained by a projectile is equal to one-fourth of its maximum range.

15.What is the dot product of two perpendicular vectors?

[A] 1
[B] 0
[C] -1
[D] 1/2

Notes:
When two vectors are perpendicular to each other, then θ = 90° and Cos 90° = θ . Therefore, A.B = A x B x Cos θ = A x B x Cos 90° = θ When two vectors are parallel to each other, then θ = θ ° and Cos θ ° = 1. Therefore, A.B = A x B x Cos θ = A x B x Cos θ ° = AB When two vectors are anti-parallel to each other, then θ =180° and Cos 180° = -1. Therefore, A.B = A x B x Cos θ = A x B x Cos 180° = -AB

16.Work done is defined as the dot product of which of the following vectors?

[A] Force and acceleration
[B] Force and area
[C] Force and instantaneous velocity
[D] Force and displacement

Correct Answer: D [Force and displacement]

Notes:
Work done is defined as the dot product of Force vector and displacement vector. W = F.s Work done is a scalar quantity. Note: Instantaneous power is defined as the dot product of Force vector and instantaneous velocity.

17.The capacity of a body to do work is known as:

[A] Energy
[B] Power
[C] Momentum
[D] Strength

Notes:
Energy of a body is the capacity or the ability of a body to do the work. Energy is a scalar quantity having magnitude but no direction. Its unit is same as that of Work S.I. unit: joule In c.g.s system, unit is erg.

18.1 electron volt of energy is equal to ____?

[A] 3.6 x 106 J
[B] 1.6 x 10-19 J
[C] 3.6 x 10-19 J
[D] 1.6 x 10-18 J

Correct Answer: B [1.6 x 10-19 J]

Notes:
Electron volt is a practical unit of energy. Some practical units of energy are: 1 erg = 10-7 J 1 calorie = 4.2 J 1 Kilowatt hour = 3.6 x 106 J 1 Electron volt(ev) = 1.6 x 10-19 J

19.What happens to the velocity of a heavy body when it undergoes an elastic collision in one dimension with a very light body at rest?

[A] it stops and comes to rest
[B] it keeps on moving with the same velocity
[C] it starts moving with half of its initial velocity
[D] it rebounds with the same velocity

Correct Answer: B [it keeps on moving with the same velocity]

Notes:
The heavy body keeps on moving with the same velocity when it undergoes an elastic collision in one dimension with a very light body at rest. Note: the body at rest starts moving with double the initial velocity of the heavy body.

20.What is the value of Universal Gravitational Constant?

[A] 6.67×10-9 N–m2 kg–2
[B] 6.67×10-10 N–m2 kg–2
[C] 6.67×1011 N–m2 kg–2
[D] 6.67×10-11 N–m2 kg–2

Correct Answer: D [6.67×10-11 N–m2 kg–2]

Notes:
The value of Universal Gravitational Constant is same throughout the universe and is equal to 6.67×10-11 Nm2 kg-2 in S.I. and 6.67×10-8 dyne cm2 g-2

21.Which of the following is NOT a conservative force?

[A] Electrostatic force
[B] Magnetic force
[C] Force in an elastic spring
[D] Frictional force

Notes:
A conservative force is a force with the property that the work done in moving a particle between two points is independent of the taken path. Examples: Electrostatic force, Magnetic force, Force in an elastic spring Frictional force is a non-conservative force.

22.Which of the following is/are correct about Kinetic energy?

[A] Kinetic energy can be positive or negative
[B] Kinetic energy is independent of frame of reference
[C] Both a and b
[D] None of the above

Correct Answer: D [None of the above]

Notes:
Kinetic energy of a body is half the product of mass of the body and square of the velocity of the body. K.E = 1/2(mv2) Kinetic energy depends on the frame of reference. Kinetic energy of a body is always positive.

23.What is the value of escape velocity for earth?

[A] 9.8 km s-2
[B] 1.6 km s-2
[C] 11.2 km s-2
[D] 7.92 km s-2

Correct Answer: C [11.2 km s-2]

Notes:
The value of escape velocity is different for different planets. For earth, this value is 11.2 km s-2.

24.Which of the following is the correct equivalent of 1 atmosphere?

[A] 1 atmosphere = 1.013 × 105Pa
[B] 1 atmosphere = 1.013 × 104Pa
[C] 1 atmosphere = 1.013 × 103Pa
[D] 1 atmosphere = 1.013 × 102Pa

Correct Answer: A [1 atmosphere = 1.013 × 105Pa]

Notes:
A common unit of pressure is the atmosphere (atm), i.e. the pressure exerted by the atmosphere at sea level (1 atm = 1.013 × 105Pa).

25.Which of the following equation represents the Torricelli’s law?

[A] (2gh)1/2
[B] √3 gh
[C] √2 gh
[D] 2gh

Notes:
Torricelli’s theorem is also called as Torricelli’s law, It states that the speed, v, of a liquid flowing under the force of gravity out of an opening in a tank is proportional jointly to the square root of the vertical distance, h, between the liquid surface and the centre of the opening and to the square root of double the acceleration due to gravity. V = (2gh)1/2

26.Which of the following represents the condition for floatation?

[A] Fb = mg
[B] Fb + mg =0
[C] Fb/ mg =1
[D] Fb = mgh

Correct Answer: A [Fb = mg]

Notes:
As per the Archimedes principle, an object will float if the buoyancy force exerted on it by the fluid balances its weight, i.e. if Fb = mg.

27.What is the unit of surface tension in c.g.s system?

[A] N/m
[B] dyne/cm
[C] erg/cm
[D] dyne cm

Notes:
The unit of surface tension is S.I system is N/m and in c.g.s system is dyne/cm. It is represented by T = force/length.

28.What happens to the time period of a spring pendulum based clock kept on the earth when it is taken to moon?

[A] Time period reduces to half
[B] Time period becomes twice
[C] Time period becomes one-sixth
[D] No change

Notes:
Time of a spring pendulum is independent of acceleration due to gravity. That is why a clock based on spring pendulum will keep proper time every where on a hill or moon or in a satellite and time period of a spring pendulum will not change inside a liquid if damping effects are neglected.

29.What happens to the frequency of the pendulum if it is suspended from the ceiling of the lift moving up ward with constant acceleration?

[A] it decreases
[B] it increases
[C] may increase or decrease
[D] No change

Notes:
If the lift is moving up ward with constant acceleration a then the time period of the pendulum decreases and frequency increases.

30.What is wavelength of a wave?

[A] square of the distance between two points having the same phase
[B] maximum distance between two points having the same phase
[C] minimum distance between two points having the same phase
[D] None of the above

Correct Answer: C [minimum distance between two points having the same phase]

Notes:
The minimum distance between two points having the same phase is called the wave length of the wave. It is represented by λ.

31.Which of the following represents the Density of a material?

[A] Mass/weight
[B] Mass/Length
[C] Mass/Volume
[D] Mass/Area

Correct Answer: C [ Mass/Volume ]

Notes:
Density is the ratio of mass to volume. It is a measure of material’s compactness. Density = Mass/Volume

32.Which of the following is the S.I. unit of density?

[A] m-2
[B] m-3
[C] kg m-2
[D] kg m-3

Correct Answer: D [ kg m-3 ]

Notes:
The SI unit of density is kg m-3. It is a positive scalar quantity. The Gaussian unit of density is the gram per cubic centimeter which is equivalent to a gram per milliliter [1 g/cm3 = 1 g/ml].

33.What is Specific Gravity of a liquid?

[A] ratio of the density of a liquid to the density of water
[B] product of the density of a substance to the density of water

[C] ratio of the density of water to the density of a liquid
[D] ratio of density of the liquid to the mass of the equal density of water

Correct Answer: A [ ratio of the density of a liquid to the density of water ]

Notes:
Specific gravity of a liquid is the ratio of the density of a substance to the density of water. The density of liquid water at standard conditions on earth is approximately 1,000 kg/m3.

34.What is the unit of Specific gravity?

[A] kg m-3
[B] kg m-2
[C] kg m-1
[D] No units

Correct Answer: D [ No units ]

Notes:
Specific gravity is a unitless quantity. Specific gravity is the ratio of two same dimensions. The dimensions of density is M1 L– 3

35.Which of the following is correct about the electromagnetic waves?

[A] They require a solid medium to travel
[B] They can travel through vacuum
[C] Electromagnetic waves can only travel through gases
[D] None of the above

Correct Answer: B [They can travel through vacuum]

Notes:
Electromagnetic waves do not necessarily require a medium – they can travel through vacuum. Light, radio waves, X-rays, are all electromagnetic waves.

36.Which of the following produces Electromagnetic waves?

[A] charges at rest
[B] charges in uniform motion
[C] accelerated charges
[D] All of the above

Notes:
Neither stationary charges nor charges in uniform motion (steady currents) can be sources of electromagnetic waves. The former produces only electrostatic fields, while the latter produces magnetic fields that, however, do not vary with time. As per Maxwell’s theory, accelerated charges radiate electromagnetic waves.

37.What is the relationship between the frequency and the pitch of a sound wave?

[A] Higher the frequency, higher the pitch
[B] Lower the frequency, higher the pitch
[C] Pitch is not dependant on the frequency
[D] None of the above

Correct Answer: A [Higher the frequency, higher the pitch]

Notes:
How the brain interprets the frequency of an emitted sound is called its pitch. The faster the vibration of the source, the higher is the frequency and the higher is the pitch,

38.Which of the following sound waves are used in echocardiography?

[A] Infrasonic
[B] Ultrasonic
[C] Between 20 Hz and 2000 Hz
[D] None of the above

Notes:
Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’.

39.Which of the following is another unit of frequency?

[A] decibel
[B] cycle per second
[C] metre per second
[D] second

Correct Answer: B [cycle per second]

Notes:
The change in density from the maximum value to the minimum value, again to the maximum value, makes one complete oscillation. The number of oscillations per unit time is the frequency of the sound wave.

40.What is a perfectly black body?

[A] A body which absorbs all the radiations incident on it
[B] A body which has zero coefficient of linear expansion
[C] A body which has zero absorptive power
[D] A body painted black on all sides

Correct Answer: A [A body which absorbs all the radiations incident on it]

Notes:
A body which absorbs all the radiations incident on it is called a perfectly black body.

41.Which of the following eye-defects is also known as far -sightedness?

[A] Myopia
[B] Hyper-metropia
[C] Cataract
[D] None

Notes:
Hypermetropia is also known as far -sightedness. A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.

42.What is the size of the image formed by a concave mirror when the object is at focus?

[A] Enlarged
[B] Point sized
[C] Same size
[D] Highly enlarged

Notes:
Highly enlarged image is formed by a concave mirror when the object is at focus.

43.Which of the following is correct NOT correct about inert electrodes?

[A] They serve as source of electrons
[B] They take part in the chemical reaction
[C] Both a and b
[D] None of the above

Correct Answer: B [They take part in the chemical reaction]

Notes:
An inert electrode is a metal submerged in an aqueous solution of ion compounds that transfers electrons rather than exchanging ions with the aqueous solution. It does not participate or interfere in the chemical reaction but serves as a source of electrons.

44.What is the direction of current through external circuit in a galvanic cell?

[A] flows from cathode to anode
[B] flows from anode to cathode
[C] flows in both direction
[D] None of the above

Correct Answer: A [flows from cathode to anode]

Notes:
Current flows from cathode to anode through external circuit.

45.What is the SI unit of magnetic flux?

[A] teslas
[B] maxwell
[C] weber
[D] Newton

Notes:
The SI unit of magnetic flux is the weber (Wb) and the CGS unit is the maxwell.

46.Which of the following is NOT correct about the force of interaction between two poles of a magnet, as per coulomb’s law?

[A] directly proportional to the product of the pole strength
[B] directly proportional to the square of the distance r between the poles
[C] Both a and b
[D] None of the above

Correct Answer: B [directly proportional to the square of the distance r between the poles]

Notes:
As per coulomb’s law, the force of interaction between two poles of a magnet is directly proportional to the product of the pole strength and inversely proportional to the square of the distance r between them.

47.Which of the following statements related to the unit curie (Ci) is correct?

[A] 1 Ci = 3.7 × 107
[B] 1 Ci = 2.7 × 109
[C] 1 Ci = 2.7 × 107
[D] 1 Ci = 3.7 × 1010

Correct Answer: D [1 Ci = 3.7 × 1010]

Notes:
There is also another unit named “curie” that is widely used and is related to the SI unit as: 1 curie = 1 Ci = 3.7 × 1010 decays per second = 3.7 × 1010 Bq

48.Which of the following is correct?

[A] 1 rutherford (Rd) = 103 decays/second
[B] 1 rutherford (Rd) = 104 decays/second
[C] 1 rutherford (Rd) = 105 decays/second
[D] 1 rutherford (Rd) = 106 decays/second

Correct Answer: D [1 rutherford (Rd) = 106 decays/second]

Notes:
The activity of a radioactive sample is said to be one rutherford. 1 rutherford (Rd) = 106 decays/second

49.What is the value of Rydberg constant?

[A] 1.0973 x 103 m-1
[B] 1.0973 x 105 m-1
[C] 1.0973 x 107 m-1
[D] 1.0973 x 109 m-1

Correct Answer: C [1.0973 x 107 m-1]

Notes:
The value of Rydberg constant is 1.0973 x 107 m-1

50.Which of these are called as Universal logic gates?

[A] NAND
[B] NOR
[C] NOT
[D] Both a and b

Correct Answer: D [Both a and b]

Notes:
The NAND gate and the NOR gate are called as universal gates as any Boolean function can be implemented without the need to use any other gate.