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Multiple choice question for engineering

Set 1

1. When one end of the rod is heated, the molecules at the hot end vibrate with higher amplitude and transmit the heat from one particle to the adjacent particle and so on. What is the process?
a) Convection
b) Conduction
c) Radiation
d) Transmittance

View Answer

Answer: b [Reason:] In the above condition, heat is transmitted by vibration of particles. Conduction is the process in which heat is transferred from hotter end to colder end without the actual motion of particles. Therefore, it is conduction.

2. Solids with weekly bonded electrons are good conductors of heat. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] Transmission of heat depends upon the outermost electrons. Therefore solids with weekly bonded electrons are good conductors of heat.

3. When potassium is added to water, it is seen that the lower region becomes warm first and becomes less dense. It then moves up and the more dense cold water comes down and the process goes on. What is the process taking place?
a) Radiation
b) Conduction
c) Convection
d) Purification

View Answer

Answer: c [Reason:] Convection is the process in which heat is transmitted from hotter end to colder end by actual movement of heated particles. Since the particles are actually moving in the above process, it is convention.

4. Why is the roof of buildings painted white?
a) Because it absorbs radiation
b) Because it reflects radiations
c) Because it is cheaper
d) Because it conducts heat

View Answer

Answer: b [Reason:] Black objects are good absorbers and radiators while white surfaces are poor absorbers and radiators. Therefore houses are painted white to keep the building cool during summer.

5. What happens when a material is heated?
a) It contracts
b) It melts
c) It expands
d) It bursts

View Answer

Answer: c [Reason:] Most materials expand on heating because the particles are moving about a higher average speed and therefore have higher energetic collision.

6. Why locations next to large water bodies tend to have a moderate climate than those further inland?
a) Because of the latitude
b) Because of specific heat of water
c) Because of the heating effects of sun
d) Because of the water in clouds

View Answer

Answer: b [Reason:] It takes a longer time to heat up or cool down a given mass of water than an equal mass of aluminium or iron. This high specific heat of water makes it easy for cooling and warming. This is why the locations next to larger water bodies tend to have a moderate climate than those further inland.

7. The outer ends of two bars A and B are at 100°C and 50° respectively. Calculate the temperature at the welded joint if they have the same cross-section and the same length and their thermal conductivities are in the ratio of A:B = 7:5
a) 79.166°C
b) 80.548°C
c) 20.157°C
d) 58.147°C

View Answer

Answer: a [Reason:] K1/K2 = (θ2-θ3)/(θ1-θ2) θ2= 79.166℃

8. What happens when you heat a china having some dark paintings engraved on it at 1000°C and then examine it in a dark room immediately?
a) The dark painting will appear much brighter
b) The whole china dish will be bright
c) The china dish doesn’t glow
d) The china dish will develop patterns

View Answer

Answer: a [Reason:] According to Kirchhoff’s law, if a body strongly absorbs a radiation of certain wavelength, it must emit strongly the radiation of same wavelength. The dark paintings are better absorbers, and therefore, also better emitters.

9. A green glass heated in a furnace when taken out in dark glows red. True or false?
a) False
b) True

View Answer

Answer: b [Reason:] Green glass, when cold, is a good absorber of red light and a good reflector of green light. When heated, it becomes a good emitter of red light in accordance with Kirchhoff’s law.

10. Two thermometers are constructed in the same way except that one has a spherical bulb and the other an elongated cylindrical bulb. Which of the two will respond quickly to temperature changes?
a) Spherical bulb
b) Elongated cylindrical bulb
c) All of the mentioned
d) None of the mentioned

View Answer

Answer: a [Reason:] A cylindrical bulb has a greater surface area than a spherical bulb of the same volume. Hence the thermometer with elongated cylindrical bulb will respond to temperature changes more quickly than the one with spherical bulb.

11. The temperature of a body can be negative on the Kelvin scale. True or false?
a) True
b) False

View Answer

Answer: b [Reason:] The temperature of a body cannot be negative on Kelvin scale because the absolute zero on the Kelvin scale is the minimum possible temperature.

12. Which of the following is an effective coolant?
a) Oil
b) Mercury
c) Water
d) Acids

View Answer

Answer: c [Reason:] The specific heat of water is very high. When it runs over hot parts of engine or machinery, it absorbs a large amount of heat. This helps in maintaining the temperature of the engine low.

Set 2

1. Any process in which the system returns to its initial state after undergoing a series of changes is known as
a) Clockwise process
b) Anticlockwise process
c) Cyclic process
d) Thermodynamic process

View Answer

Answer: c [Reason:] Any process in which the system returns to its initial state is known as a cyclic process. The change in internal energy after complete cycle is zero because the system returns to its initial state.

2. A gas does work during isothermal expansion. The source of mechanical energy so produced is the internal energy of the gas itself. True or false?
a) True
b) False

View Answer

Answer: b [Reason:] By the first law of thermodynamics, ∆Q=∆U+∆W. But for an isothermal process, ∆U is zero, so∆Q=∆W. Thus the energy required for doing mechanical work during an isothermal process is obtained as heat by the gas from the surroundings.

3. An ideal gas is pressed at constant temperature. Its internal energy
a) Decreases
b) Increases
c) First increases and then decreases
d) Remains the same

View Answer

Answer: d [Reason:] When an ideal gas is pressed at constant temperature, its internal energy remains the same because the internal energy of the gas depends only on its temperature.

4. When a gas is suddenly compressed, its temperature decreases. True or false?
a) True
b) False

View Answer

Answer: b [Reason:] Sudden compression of gas gives an adiabatic process. The work done in compressing the gas increases the internal energy of the gas. Hence the temperature of the gas rises.

5. A monoatomic ideal gas, initially at temperature T1 is enclosed in a cylinder fitted with a frictionless piston. The gas is allowed to expand adiabatically to a temperature T2 by releasing the piston suddenly. L1 and L2 are the lengths of the gas column before and after expansion respectively, then T1/T2 is given by
a) (L1/L2 )(2/3)
b) L1/L2
c) L2/L1
d) (L2/L1 )(2/3)

View Answer

Answer: d [Reason:] For an adiabatic expansion, (TV)(γ-1)=constant T1 (V1)(γ-1)=T2 (V2)(γ-1) For a monoatomic gas, γ=5/3 If A is the area of cross-section of the piston, then T1/T2 =(V2/V1)(γ-1) T1/T2 =((AL2)/(AL1))(2/3)

6. An ideal gas heat engine is operating between 227°C and 127°C. It absorbs 104 J of heat at the higher temperature. The amount of heat converted into work is
a) 2000 J
b) 4000 J
c) 8000 J
d) 5600 J

View Answer

Answer: a [Reason:] Ƞ=1-T2/T1 =1-(273+127)/(273+227)=1-400/500=1/5 W=ȠQ1=1/5×104=2000J

7. Internal energy change, when a system goes from state A and B is 40 kJ mole-1. If the system goes from A and B by a reversible path and returns to state A by an irreversible path, what would be the net change in internal energy?
a) 40 kJ
b) Greater than 40 kJ
c) Later than 40 kJ
d) Zero

View Answer

Answer: d [Reason:] As the system returns to the initial state A, the change in internal energy is zero.

8. Even Carnot engine cannot give 100% efficiency, because we cannot
a) Prevent radiation
b) Find ideal sources
c) Reach absolute zero temperature
d) Eliminate friction

View Answer

Answer: a [Reason:] The efficiency of a Carnot engine will be 100% when its sink is at 0K. But the temperature 0K cannot be realised in practice, so the efficiency is never 100%.

9. Assertion: The temperature of a gas does not change, when it undergoes an adiabatic expansion. [Reason:] During an adiabatic process, heat energy is exchanges between a system and its surrounding
a) Both assertion and reason are true and reason is correct explanation of the assertion
b) Both assertion and reason are true but reason is not correct explanation of the assertion
c) Assertion is true but reason is false
d) Both assertion and reason are false

View Answer

Answer: d [Reason:] Both the assertion and reason are false. Temperature decreases during adiabatic expansion while it increases during adiabatic compression.

10. We consider a thermodynamic system. If ∆U represents the increase in its internal energy and W, the work done by the system; which of the following statements are true?
a) ∆U=-W in an isothermal process
b) ∆U=W in an isothermal process
c) ∆U=-W in an adiabatic process
d) ∆U=W in an adiabatic process

View Answer

Answer: c [Reason:] In an adiabatic process, ∆Q=0 ∆U=∆Q-∆W=0-W=-W

Set 3

1. A faulty thermometer has its fixed points marked as 5° and 95°. Temperature of a body as measured by the faulty thermometer is 59°. Find the correct temperature of the body on Celsius scale.
a) 60°C
b) 40°C
c) 20°C
d) 0°C

View Answer

Answer: a [Reason:] (TC-0)/(100-0)=(Temperature on faulty scale-Lower fixed point)/(Upper fixed point-Lower fixed point) (TC-0)/100=(59-5)/(95-5)=54/90 TC=60°C

2. Temperature is a microscopic concept. True or false?
a) True
b) False

View Answer

Answer: b [Reason:] Temperature is a macroscopic concept. It is related to the average kinetic energy of a large number of molecules forming a system. It is not possible to define the temperature for a single molecule.

3. The thermometer bulb should have
a) High heat capacity
b) No heat capacity
c) Small heat capacity
d) Varying heat capacity

View Answer

Answer: c [Reason:] The thermometer bulb having small heat capacity will absorb less heat from the body whose temperature is to be measured. Hence the temperature of that body will practically remain unchanged.

4. Calorie is defined as the amount of heat required to raise the temperature of 1g of water by 1°C and it is defined under which of the following conditions?
a) From 14.5°C to 15.5°C at 760mm of Hg
b) From 98.5°C to 99.5°C at 760mm of Hg
c) From 13.5°C to 14.5°C at 76mm of Hg
d) From 3.5°C to 4.5°C at 76mm of Hg

View Answer

Answer: a [Reason:] One calorie is defined as the heat required to raise the temperature of 1g of water from 14.5°C to 15.5° at 760mm of Hg

5. Compared to burn due to air at 100°C, a burn due to steam at 100°C is
a) More dangerous
b) Less dangerous
c) Equally dangerous
d) Not dangerous

View Answer

Answer: a [Reason:] Compared to burn due to air at 100°C, a burn due to steam at 100°C is more dangerous due to the additional heat possessed by steam.

6. 540g of ice at 0°C is mixed with 540g of water at 80°C. The final temperature of mixture is
a) 0°C
b) 40°C
c) 80°C
d) Less than 0°C

View Answer

Answer: a [Reason:] Heat gained by ice = Heat lost by water at 80°C 540×80+540×1×θ=540×1×(80-θ) θ=0°C

7. An ideal black body is thrown into a furnace. The black body is room temperature. It is observed that
a) Initially, it is darkest body and at later times the brightest
b) At all times it is the darkest body
c) It cannot be distinguished at all times
d) Initially, it is the darkest body and at later it cannot be distinguished

View Answer

Answer: a [Reason:] Initially at lower temperature, it absorbs the entire radiations incident upon it. So, it is the darkest body. At later times, when it attains the temperature of the furnace, the black body radiates maximum energy. It appears brightest of all bodies.

8. If the sun were to increase in temperature from T to 2T and its radius from R to 2R, then the ratio of the radiant energy received on earth to what it was previously, will be
a) 4
b) 16
c) 32
d) 64

View Answer

Answer: d [Reason:] Energy radiated by the sun per second, E = σAT4= σ×4πR2×T4 When its radius and temperature change to 2R and 2T respectively, E=σ×4π(2R)2×(2T)4 E/E=64

9. On a hilly region, water boils at 95°C. The temperature expressed in Fahrenheit is
a) 100°F
b) 203°F
c) 150°F
d) 20.3°F

View Answer

Answer: b [Reason:] (F-32)/9=C/5=95/5 F = 171+32 = 203°F

10. A composite rod made of copper (1.8×10(-5) K(-1)) and steel (α=1.2×10(-5) K(-1)) is heated. Then
a) It bends with steel on concave side
b) It bends with copper on concave side
c) It does not expand
d) Data is insufficient

View Answer

Answer: a [Reason:] αcoppersteel Copper expands more than steel. So rod bends with copper on convex side and steel on concave side.

11. Temperatures of two stars are in ratio 3:2. If wavelength of maximum intensity of first body is 4000 Å, what is corresponding wavelength of second body?
a) 9000 Å
b) 6000 Å
c) 2000 Å
d) 8000 Å

View Answer

Answer: b [Reason:] ((ʎm))/ʎm =T/T =3/2 (ʎm)=3/2 ʎmm)=3/2×4000=6000Å

12. A piece of blue glass heated to a high temperature and a piece of red glass at room temperature, are taken inside a room that is dimly lit, then
a) The blue piece will look blue and red will look as usual
b) Red looks brighter and blue looks ordinary blue
c) Blue shines like brighter red compared to the red pieces
d) Both the pieces will look equally red

View Answer

Answer: c [Reason:] According to Stefan’s law, E is proportional to T4 As the temperature of blue glass is more than that of red glass, so it will appear brighter than red glass.

Set 4

1. In a thermal process, pressure of a fixed mass of a gas is changed in such a manner that the gas molecules give out heat of 30J and work of 10J is done on the gas. If the initial internal energy of the gas was 40 J, then the final internal energy will be
a) 30 J
b) 20 J
c) 60 J
d) 40 J

View Answer

Answer: c [Reason:] ∆Q=(Uf-Ui)+∆W 30=Uf-40+10 Uf=60J

2. A system, after passing through different states returns back to its original state, is called
a) Cyclic process
b) Isothermal process
c) Adiabatic process
d) Isobaric process

View Answer

Answer: a [Reason:] A process in which the system after undergoing a series of changes returns to its initial state is called a cyclic process.

3. Which of the following parameters does not characterized the thermodynamic state of matter?
a) Temperature
b) Pressure
c) Work
d) Volume

View Answer

Answer: c [Reason:] Work is not a state variable. It is a mod of transfer of energy from system to surrounding or vice versa.

4. Calculate the work done if temperature is changes from 0°C to 200°C at one atmosphere
a) 100 cal
b) 200 cal
c) 400 cal
d) 800 cal

View Answer

Answer: c [Reason:] W=P∆V=R∆T W=2calK-1×200K W=400cal

5. Assertion: When a glass of hot milk placed in a room is allowed to cool, its entropy decreases [Reason:] Allowing hot object to cool does not violate the second law of thermodynamics
a) Both assertion and reason are true and reason is correct explanation of the assertion
b) Both assertion and reason are true but reason is not correct explanation of the assertion
c) Assertion is true but reason is false
d) Both assertion and reason are false

View Answer

Answer: b [Reason:] Both the assertion and reason are true but the reason is not the correct explanation of the assertion. As the milk cools, its temperature decreases. The decrease in temperature takes the milk to a lesser disorderly state. As the entropy is a measure of disorder, the entropy of the milk decreases.

6. Which of the following is not a state function?
a) Work done at constant pressure
b) Enthalpy
c) Work done by conservative force
d) Work done by non0conservative force

View Answer

Answer: d [Reason:] Work done by non-conservative force is not a state of function. The work done will be different along different paths between two given states of the system.

7. The inside and outside temperature of a refrigerator are 273K and 303K respectively. Assuming that refrigerator cycle is reversible, for every joule of work done, the heat delivered to the surrounding will be
a) 10 J
b) 20 J
c) 30 J
d) 50 J

View Answer

Answer: a [Reason:] β=Q2/W=T2/(T1-T2 )=273/(303-273) Q2=273W/30=273/30×1J=9J Q1=Q2+W=9+1=10J

8. The door of a domestic refrigerator is kept open while the switch is on. Then the room will
a) Get heated
b) Ger neither heated nor cooled
c) Gets cooled
d) Gets heated first and then cools

View Answer

Answer: a [Reason:] Temperature of the room will rise because refrigerator takes less heat from the room and rejects more heat.

9. A Carnot engine working between 300 K and 600 K has a work output of 800 J per cycle. The amount of heat energy supplied to the engine from source per cycle is
a) 1200J
b) 1600J
c) 2400J
d) 3200J

View Answer

Answer: b [Reason:] Ƞ=W/Q1 =1-T2/T1 =1-300/600=1/2 Q1=2W=2×800=1600J

10. Heat capacity of a substance is infinite. It means
a) Heat is given out
b) Heat is taken out
c) No change in temperature
d) Heat is first given out and then taken out

View Answer

Answer: c [Reason:] Whatever amount of heat is taken in or given out by a substance of infinite heat capacity, there is no change in its temperature.

Set 5

1. Two racing cars of masses m1 and m2 are moving in circles of radii r1 and r2 respectively. Their speeds are such that each makes a complete circle in the same time t. The ratio of the angular speeds of the first two to the second car will be
a) 1:1
b) r1:r2
c) m1:m2
d) m1 m2:r1 r2

View Answer

Answer: a [Reason:] ω=v/r=2π/T As both cars take some time for one revolution, so ω is same for both the cars.

2. A flywheel is attached to an engine to
a) Increase its speed
b) Decrease its speed
c) Help in overcoming the dead point
d) Decrease its energy

View Answer

Answer: c [Reason:] Due to its large inertia of motion, a flywheel helps the engine to overcome the dead points.

3. Three identical metal balls, each of the radius r are placed touching each other on a horizontal surface such that an equilateral triangle is formed when centres of three balls are joined. The centre of the mass of the system is located at
a) Line joining centres of any two balls
b) Centre of one of the balls
c) Horizontal surface
d) Point of intersection of the medians

View Answer

Answer: d [Reason:] The centre of mass of the system lies at the point of intersection of the medians that is at the centroid of the equilateral triangle.

4. A solid sphere of radius R is placed on smooth horizontal surface. A horizontal force F is applied at height h from the lowest point. For the maximum acceleration of centre of mass, which is correct?
a) h=R
b) h=2R
c) h=0
d) No relation between h and R

View Answer

Answer: d [Reason:] The smooth horizontal surface does not provide any friction. The sphere does not roll. Hence the acceleration of centre of mass of the sphere is independent of the position of the applies force. There is no relation between h and R.

5. Statement 1: The earth is slowing down and as a result the moon is coming nearer to it
Statement 2: The angular momentum of the earth moon system is not conserved
a) Both statement 1 and 2 are true and statement2 is the correct explanation of the statement1
b) Both statement 1 and 2 are true but the statement 2 is not the correct explanation of the statement1
c) Statement 1 is true but the statement 2 is false
d) Statement 1 and 2 are false

View Answer

Answer: d [Reason:] Both the assertion and reason are false. The earth is not slowing down. The angular momentum of earth-moon system is conserved.

6. Statement 1: If ice caps of the pole melt, the day length will shorten
Statement 2: Ice flows towards the equator and decreases the moment of inertia of the earth and hence increases the frequency of rotation of the earth.
a) Both statement 1 and 2 are true and statement2 is the correct explanation of the statement 1
b) Both statement 1 and 2 are true but the statement 2 is not the correct explanation of the statement 1
c) Statement 1 is true but the statement 2 is false
d) Statement 1 and 2 are false

View Answer

Answer: d [Reason:] Both the assertion and reason are false. As the polar ice melts, water so formed flows towards the equator. This increases the moment of inertia. To conserve angular momentum, frequency of rotation decreases and the day length becomes longer.

7. The direction of angular velocity vector is along
a) The tangent to the circular path
b) The inward radius
c) The outward radius
d) The axis of rotation

View Answer

Answer: d [Reason:] If we wrap the right hand around the axis of rotation with the fingers pointing in the direction of rotation, then the thumb points in the direction of angular velocity.

8. The motion of planets in the solar system is an example of the conservation of
a) Mass
b) Linear momentum
c) Angular momentum
d) Energy

View Answer

Answer: a [Reason:] The motion of planets around the sun is an example of the conservation of angular momentum.

9. A body of mass M while falling vertically downwards under gravity breaks into two parts, a body B of mass 1/3 M and body C of mass2/3 M. The centre of mass of bodies B and C taken together shifts compared to that of body A towards
a) Body C
b) Body B
c) Depends on height of braking
d) Does not shift

View Answer

Answer: d [Reason:] The centre of mass bodies B and C does not shift compared to body A. It continues to move vertically downwards under the effect of gravity. This is because there is no new external force acting on the system.

10. The instantaneous acceleration of the point of contact during rolling is zero. True or false?
a) True
b) False

View Answer

Answer: b [Reason:] As the body is rotating, its instantaneous acceleration cannot be zero.