West Bengal PSC Previous Year Physics Questions with Answers (Part- 4)

 

In this post we list and solve the West Bengal Public Service Commission's previous  year Physics question. In this post we arrange the question topic wise. This post is the Part-4 of this series.

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View Part-2 

View Part-3 

Actually, this Physics series is the part of WBPSC Previous Year SCIENCE series.

Electricity

Q. For measuring flow of current, the device is used       
[WBPSC Miscellaneous Exam- 2012(1st)]

1. Voltmeter
2. Galvanometer
3. Ammeter
4. Potentiometer
   

C. Ammeter

Explanation: 

•  Ammeter is used to measure current flow in the circuit.
  
•  Voltmeter is used to measure potential difference.
  
• Galvanometer is used to detect the current flow in a circuit.
• Potentiometer is used to measure potential difference, emf of a cell etc.
  

Q. What is the unit of power?       
[WBPSC Miscellaneous Exam- 2012(1st)]

1. Half life
   
2. Watt
   
3. Volt
   
4. Jule
   

B. Watt

Explanation: 

• Watt is unit of power.
• Volt is unit of potential difference.
• Joule is unit of energy.
  

Q. Kilo-Watt-Hour is the unit of      
[WBPSC Miscellaneous Exam- 2012(2nd)]

1. Power
   
2. Force
   
3. Energy
   
4. Momentum
   

C. Energy

Explanation: Kilo-Watt is the unit of power and hour is the unit of time.

 Power=energy/time
So, Power×time=(energy/time)×time=energy

Q. With increase in temperature the resistance of a pure conductor       
[WBCS Preliminary Exam- 2016]

1. first increase and then decrease
   
2. remains same
   
3. increase
   
4. decrease
   

C. increase

Explanation:

• With the increase of temperature, resistance of pure conductor increases.
• With the increase of temperature, resistance of semiconductor decreases.
  

Q. The electric appliances in a house are connected      
[WBCS Preliminary Exam- 2017]

1. in series
   
2. in parallel
   
3. either in series or parallel
   
4. both in series and in parallel
   

B. in parallel

Explanation: 

• Electric appliances (light, fan, television etc.) in a house are connected in parallel.
• Fuse, MCB (Miniature Circuit Breaker), any kind of circuit breaker are connected in series. 
  

Q. A battery consists of 10 cells, each of emf 1V. If 2 cells are wrongly connected, the emf of the battery becomes       
[WBCS Preliminary Exam- 2021]

1. 8V
   
2. 10V
   
3. 6V
   
4. 12V
   

C. 6V

Explanation:
Here, we assume cells are connected in series.
If cells are connected in series, emf of cells are to be added to get emf of battery.
If one cell is wrongly connected, emf of two cells together become zero.

In this question, 2 cells wrongly connected.
So, emf of 2×2=4 cells together become zero.
Hence, emf of remaining (10-4)=6 cells are to be added for getting the emf of battery.
Therefore, if two cells are wrongly connected, emf of battery becomes 1×6=6V.

Q. Pure silicon at 0K is       
[WBCS Preliminary Exam- 2021]

1. semiconductor
   
2. metal
   
3. insulator
   
4. superconductor
   

C. insulator

Explanation:
Resistance of Conductor decreases with the increase of temperature and vice versa.
Resistance of Semiconductor increases with the increase of temperature and vice versa.

Silicon is a semiconductor.
Resistance of semiconductor decreases with the decrease of temperature.
Hence, pure silicon at 0K is insulator.

Q. If the length of the filament of a heater is reduced by 10%, the power of the heater will        
[WBCS Preliminary Exam- 2021]

1. increase by about 9%
   
2. increase by about 11%
   
3. increase by about 19%
   
4. decrease by about 10%
   

B.increase by about 11%

Explanation:  We know that

I=current
V=potential difference
R=resistance

We have,

ρ=resistivity of the material of the wire
l=length of the wire
A=cross sectional area of the wire
So,

Let, at first, for the heater, variables were V, A, ρ, l.
If the length of the filament of the heater is reduced by 10%, the length will be

Power of the heater at first,

Power of the heater after 10% reduction of filament,

It is clear that P₁<P₂
So, Power increased,

Therefore, percentage of increase

Therefore, if the length of the filament of a heater is reduced by 10%, the power of the heater will increase by about 11%.

Magnet

Q. At magnetic poles, the angle of dip is            [WBCS Preliminary Exam- 2019]

1. 45°
   
2. 30°
   
3. zero
   
4. 90°
   

D. 90°

Explanation: Angle of dip is an angle between the earth's magnetic field and the horizontal plane.

• Angle of dip at the equator is 0° (zero degree).
• Angle of dip at the magnetic poles is 90°.
  

Wave

Q. All electromagnetic wave has the same       
[WBCS Preliminary Exam- 2018]

1. frequency
   
2. amplitude
   
3. wave length in vacuum
   
4. speed in vacuum
   

D. Speed in vacuum

Explanation:

• Frequency: Number of full cycle completed by a wave in unit time is known as frequency.
• In vacuum the speeds of all electromagnetic waves (Radio wave, visible light, x-ray, gamma ray) are same and it is 3×10⁸m/s=3×10¹⁰cm/s.
  

Q. The wave produced by motor boat sailing on water are         
[WBCS Preliminary Exam- 2021]

1. transverse
   
2. longitudinal
   
3. longitudinal and transverse
   
4. stationary
   

C.longitudinal and transverse

Explanation:

• Longitudinal wave: If the directions of vibration of particles of medium and the wave traverse are same, that wave is known as longitudinal wave.
• Transverse wave: If direction of the vibration of particle of the medium and the wave travels are perpendicular to each other that wave are known as transverse wave.
  

Fluid

Q. Hydraulic press is based on     
[WBCS Preliminary Exam- 2015, 2021]

1. Archimedes' law
   
2. Pascal's law
   
3. Reynold's law
   
4. Bernoulli's law
   

B. Pascal's law

Explanation: 

• Pascal's law: Pressure applied on a fluid rest in closed container is transmitted every point of that fluid without change in magnitude.
• Archimedes' law: The upward buoyant force that is exerted on a body immersed in a fluid (partially or fully submerged), is equal to the weight of the fluid displaced by the body. This force acts to the upward direction.
• Reynold's law: According to this law, we can determine the type of flow pattern of a fluid (laminar or turbulent) while flowing through pipe, seeing a dimensionless quantity known as Reynold's Number.
  Reynold's Number=(ρVD)/μ
  ρ=density of the fluid
  V=Velocity of flow
  D=diameter of the pipe
  μ=viscosity of the fluid
  If the Reynold's number is greater than 2000, the flow through the pipe will be turbulent.
  If the Reynold's number is less than 2000, the flow through the pipe will be laminar.
• Bernoulli's law: The total mechanical energy of the flowing fluid comprising the gravitational potential energy of elevation, the energy associated with the fluid pressure and the kinetic energy of the fluid motion remains constant.
  

Q. Water rises up a capillary tube because of           [WBCS Preliminary Exam- 2015]

1. elasticity
   
2. Surface tension
   
3. viscosity
   
4. its density
   

B. Surface tension

Explanation: Rises of water in capillary tube depends on surface tension, cohesive force, adhesive force.

• Surface tension: Surface tension is the tendency of liquid surface at rest to shrink into the minimum surface area possible.
• Elasticity: Elasticity is the property which resist the force which tries to deform the material and due to this property the deform material returns to its original shape when the force which tries to deform is removed.
• Viscosity: This is a physical quantity which refers the resistance to flow. Low viscosity means, it is easy to flow.
• Density: Density of a material represents the mass of unit volume of that material.
  Density=mass/volume.
  

Q. A shaving brush is dipped in water. When taken out the hairs of the brush are seen to be drawn together due to            [WBCS Preliminary Exam- 2017]

1. Surface tension of water
   
2. viscosity of water
   
3. elasticity of the hairs of the brush
   
4. temperature difference between air and water
   

A. Surface tension of water

Explanation: 

• Surface tension: Surface tension is the tendency of liquid surface at rest to shrink into the minimum surface area possible.
• Elasticity: Elasticity is the property which resist the force which tries to deform the material and due to this property the deform material returns to its original shape when the force which tries to deform is removed.
• Viscosity: This is a physical quantity which refers the resistance to flow. Low viscosity means, it is easy to flow.

It may be seemed that option-(C) "Elasticity of the hairs of the brush" is also the correct option. But, it is not. For elasticity, after removing the force tried to deform, the body comes back to its original shape. Here, in this case there is no such force that tried to deform and after take out of the water, the brush is actually squeezed (i.e. it is actually deformed).

Q. A body is floating in a liquid partly immersed. The body and the liquid are taken to moon. The body            [WBCS Preliminary Exam- 2018]

1. will continue to float as before
   
2. floats with greater part immersed
   
3. floats with lesser part immersed
   
4. will sink
   

A. will continue to float as before

Explanation: 

Archimedes' Principle: The upward buoyant force that is exerted on a body immersed in a fluid (partially or fully), is equal to the weight of the fluid displaced by the body.

A body is floating means, the weight of the body same as buoyant force.
mg=ρVg

m=mass of the body
g=acceleration due to gravity
ρ=density of the liquid
V=Volume of liquid displaced by the body

Here, mg=ρVg
So, m=ρV   .......(1)

Now, if the body and liquid are taken to moon, the shape, mass, density of the body and liquid obviously do not change. Only acceleration due to gravity will be changed.
In moon, acceleration due to gravity is (1/6) of that of the earth i.e (1/6)g.

So, in the moon weight of the body will be m(g/6).
Now, m(g/6)=ρV(g/6)   [using equation(1)]
It means, the volume of displaced water does not change i.e. the immerse portion of the body remains same.

Hence, the answer will be "the body will continue to float as before."

Q. Two cars, passing each other at high speed, are in danger of side swiping because          
[WBCS Preliminary Exam- 2019]

1. of the increasing in air pressure in the space between them.
   
2. of decrease in the velocity of air molecules between them.
   
3. of decrease in air pressure in the space between them.
   
4. of the increase in the velocity of air molecules between them.
   

C. of decrease in air pressure in the space between them.

Explanation: According to Bernoulli's theorem, if the velocity of fluid (flowing horizontally) is increased, the pressure will be decreased.
When, two cars pass each other at high speed, the velocity  of the air near them increases and eventually the pressure decreases.
As the pressure of the air between two cars decreases, the high air pressure (comparatively) of other sides force the car which may lead side swiping.

Q. A boat floating in a tank is carrying some passengers. If the passengers drink water from the tank, how will it affect he water level of the tank?      
[WBCS Preliminary Exam- 2021]

1. It will go down.
   
2. It will rise.
   
3. It will depend on the atmospheric pressure.
   
4. It will remain same.
   

D. It will remain same.

Explanation:
Archimedes' Principle: According to this principle, the magnitude of buoyant force is equal to the weight of water displaced by the body.
Direction of buoyant force is upward and weight is downward. 

Here, a boat is floating in a tank, carrying some passengers.
The boat is floating means, the buoyant force is equal to the weight of the boat.
Now, if the passengers drink water from the tank, the weight of the boat (boat+passengers) will increase and water level will decrease.

Due to the increased weight, boat  will immerse more and displace more water to increase buoyant force.
According to Archimedes;s principle the boat will actually displace as much water as the passengers drink from the tank.
Due to displacement of water, the level of water will increase and in-fact, it will reach at the level before [as the drunken water and displaced are of same amount].

Thermodynamics

Q. A reaction is spontaneous when             [WBCS Preliminary Exam- 2017]

1. ΔG=−ve
   
2. ΔH=−ve
   
3. ΔS=+ve
   
4. ΔS=−ve
   

A. ΔG=−ve

Explanation:
The mathematical formula for Gibbs free energy is given  by
ΔG=ΔH−TΔS

ΔG= Change in Gibbs free energy
ΔH= change in enthalpy
T= Temperature in kelvin scale
ΔS= Change in entropy 

ΔG=+ve ⇒ the reaction is non-spontaneous
ΔG=−ve ⇒ the reaction is spontaneous
ΔG=0 ⇒ the reaction is in equilibrium

Semiconductor

Q. LED stands for            [WBCS Preliminary Exam- 2015]

1. Light emitting device
   
2. Light emitting diode
   
3. Light encapsulated device
   
4. Light emitting dots
   

B.Light emitting diode

Explanation: LED (Light emitting diode) is a semiconductor device which emit light when current flow through it.

Astronomy

Q. What is the full form of SCM?            [WBPSC Miscellaneous Exam-2018]

1. Standard Cosmological Modes
   
2. Strong Cosmological Model
   
3. Stable Cosmological Model
   
4. Strict Cosmological Model
   

A. Standard Cosmological Model

Explanation: SCM refers to Standard Cosmological Model in Cosmology.

Q. One of the characteristics of the atmosphere of prebiotic primitive earth was :                 [WBCS Preliminary Exam-2015]

1. Absence of hydrogen
   
2. Absence of water vapour
   
3. Absence of nitrogen
   
4. Absence of oxygen
   

D. Absence of Oxygen

Explanation: In prebiotic primitive earth's atmosphere, there was almost no oxygen. There was nitrogen, hydrogen, carbon dioxide, water vapour.
Since, there was no free oxygen, there was no life on the earth.

Q. Satellites provide information about            [WBCS Preliminary Exam-2015]

1. Forest and vegetative cover
   
2. River and their courses
   
3. Advancing storms and cyclones
   
4. All of the above
   

D.All of the above

Explanation: Satellites provide information about forest and vegetative cover, river and its courses, storms and cyclone, clouds etc.

Q. Astronomy means study of the        
[WBCS Preliminary Exam-2016]

1. Moon
   
2. Stars
   
3. Sky
   
4. Sun
   

A. Moon;  B. Stars; C. Sky; D. Sun

Explanation: Astronomy is the study of Sun, moon, galaxies and other non-Earthly bodies and phenomena.
"Astronomy" literally means "law of stars" or "cultural of stars".

Q. 'Perseverance' rover was successfully landed by NASA on the surface of    
[WBCS Preliminary Exam-2021]

1. the Moon
   
2. the Mars
   
3. the Jupiter
   
4. the Sun
   

B.the Mars

Explanation:  'Perseverance' rover was successfully landed by NASA (National Aeronautics and Space Administration) on the surface of the Mars.
It was the part of NASA's mission Mars-2020.

Q. The ratio of the diameters of moon and earth is nearly      
[WBCS Preliminary Exam-2021]

1. 1:2
   
2. 1:5
   
3. 1:4
   
4. 1:8
   

C. 1:4

Explanation:
Diameter of earth is 12742km.
Diameter of moon is 3474.8km.
Therefore, ratio of diameter of moon to earth is
3474.8:12742
=3474.8/12742
≈0.2727

(1/4)=0.25
Therefore, the ratio of diameters of moon and earth is nearly 1:4.

West Bengal PSC Previous Year Physics Questions with Answers Part-1

West Bengal PSC Previous Year Physics Questions with Answers Part-2

West Bengal PSC Previous Year Physics Questions with Answers Part-3 

WBPSC Previous Year COMPUTER Question with Answer 

WBPSC Previous Year SCIENCE Science 

WBPSC Previous Year BIOLOGY Question wirh Answers 

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