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Multiple choice question for engineering

Set 1

1. On which factor does the average kinetic energy of gas molecules depend??
a) Nature of the gas
b) Temperature
c) Volume
d) Mass

View Answer

Answer: b [Reason:] The average kinetic energy of a gas molecule depends only on the absolute temperature of the gas and is directly proportional to it.

2. What is the average velocity of the molecules of an ideal gas?
a) Infinity
b) Constant
c) Unstable
d) Zero

View Answer

Answer: d [Reason:] The average velocity of the molecules of an ideal gas is zero, because the molecules possess all sorts of velocities in all possible directions so their vector sum and hence the average is zero.

3. The ration of the speed of sound in nitrogen gas to that in helium gas, at 300 K is
a) √(2/7)
b) √(1/7)
c) √3/5
d) √6/5

View Answer

Answer: c [Reason:] v=√(γRT/M) v(N2 )/v(He) =√(γ(N2)/γHe ×MHe/M(N2))=√((7/5)/(5/3)×4/28)=√3/5

4. Cooking gas containers are kept in a lorry moving with uniform speed. The temperature of the gas molecules inside will
a) Increase
b) Decrease
c) Remain the same
d) Decreases for some, while increase for others

View Answer

Answer: c [Reason:] The centre of mass of the gas molecules moves with uniform speed along with the lorry. As there is no change in relative motion, the translational kinetic energy and hence the temperature of the gas molecules will remain the same.

5. At Boyle’s temperature
a) Joule’s effect is positive
b) Van der Waal’s equation becomes zero
c) Gases obey Boyle’s law
d) Water solidifies

View Answer

Answer: c [Reason:] At Boyle’s temperature, a gas obeys Boyle’s law to a high degree of accuracy. Above and below this temperature, the gas deviates from Boyle’s law.

6. For Boyle’s law to hold good, the gas should be
a) Perfect and of constant mass and temperature
b) Real and of constant mass and temperature
c) Perfect and at constant temperature but variable mass
d) Real and at constant temperature but variable mass

View Answer

Answer: a [Reason:] Boyle’s law is valid for a constant mass of a perfect gas at a given temperature

7. A gas behaves as an ideal gas at
a) Low pressure and high temperature
b) Low pressure and low temperature
c) High pressure and low temperature
d) High pressure and high temperature

View Answer

Answer: a [Reason:] A gas behaves as an ideal gas at low pressure and high temperature when the attractive forces between the molecules become negligible

8. The temperature of gas is held constant, while its volume is decreased. The pressure exerted by the gas on the wall of the container increases, because its molecules
a) Strike the walls with higher velocities
b) Strike the walls with large farce
c) Strike the walls more frequently
d) Are in contact with the walls for a shorter time

View Answer

Answer: c [Reason:] When the volume is decreased, the gas molecules strike the walls more frequently

9. A bulb contains one mole of hydrogen mixed with one mole of oxygen at temperature T. The ratio of rms values of velocity of hydrogen molecules to that of oxygen molecules is
a) 1:16
b) 1:4
c) 4:1
d) 16:1

View Answer

Answer: c [Reason:] vrms=√(RT/m) For constant temperature, (vrms (H2))/(vrms (O2) )=√(M(O2)/M(H2))=√(32/2)=4:1

10. Statement: The root mean square and most probable speeds of the molecules in a gas is symmetrical [Reason:] The Maxwell distribution for the speed to molecules in a gas is symmetrical
a) Both statement and reason are true and reason is the correct explanation of the statement
b) Both statement and reason are true but reason is not correct explanation of the statement
c) Statement it true but reason is false
d) Both statement and reason are false

View Answer

Answer: d [Reason:] Both the statement and reason are false. The two speeds are different from each other. Also, the Maxwell distribution for the speed to molecules in gas is symmetrical.

11. The degree of freedom of a triatomic gas is
a) 1
b) 2
c) 6
d) 8

View Answer

Answer: c [Reason:] A triatomic gas molecule has 3 degrees of freedom due to translator motion and 3 degrees of freedom due to rotator motion.

Set 2

1. Which of the following is a unique property of laser?
a) Directional
b) Speed
c) Coherence
d) Wavelength

View Answer

Answer: c [Reason:] Coherence is an important characteristic of laser beam because in laser beams, the wave trains of same frequency are in phase/ Due to high coherence it results in an extremely high power.

2. Which of the following is an example of optical pumping?
a) Ruby laser
b) Helium-Neon laser
c) Semiconductor laser
d) Dye laser

View Answer

Answer: a [Reason:] The atoms of Ruby are excited with the help of photons emitted with the help of photons emitted by an external optical source. The atoms absorb energy from photos and raises to excited state. Therefore Ruby laser is an example of optical pumping.

3. When laser light is focussed on a particular area for a long time, then that particular area alone will be heated. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] Laser beam has very high intensity, directional properties and coherence. When it is focussed on a particular area for a long time, then the area alone will be heated and the other area will remain as such. This is called thermal effect.

4. Calculate the wavelength of radiation emitted by an LED made up of a semiconducting material with band gap energy 2.8eV.
a) 2.8 Å
b) 4.3308 Å
c) 5548.4 Å
d) 4430.8 Å

View Answer

Answer: d [Reason:] E = hc/ʎ Therefore, ʎ = hc/E ʎ = 4430.8 Å

5. Calculate the number of photons, from green light of mercury (ʎ = 4961 Å),
required to do one joule of work.
a) 4524.2×1018/m3
b) 2.4961×1018/m3
c) 2.4961/m3
d) 2.4961/m

View Answer

Answer: b [Reason:] E = hc/ʎ E = 4.006×10-19 Joules Number of photons required = (1 Joule)/(4.006×10-19 ) N = 2.4961×1018/m3

6. Which of the following can be used for generation of laser pulse?
a) Ruby laser
b) Carbon dioxide laser
c) Helium neon laser
d) Nd- YAG laser

View Answer

Answer: d [Reason:] Since Nd YAG laser has a higher thermal conductivity than other solid state lasers, it lends itself for generation of laser pulses at a higher pulse repetition rate or a quasi continuous wave operation.

7. What is the need to achieve population inversion?
a) To excite most of the atoms
b) To bring most of the atoms to ground state
c) To achieve stable condition
d) To reduce the time of production of laser

View Answer

Answer: a [Reason:] When population inversion is achieved, the majority of atoms are in the excited state. This causes amplification of the incident beam by stimulated emission. Thus the laser beam is produced.

8. Laser is called as non-material knife. True or false?
a) False
b) True

View Answer

Answer: b [Reason:] In laser surgery, without knife, bloodless operation, cutting tissues etc can be made, hence laser is called non-material knife.

9. DVD uses laser. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] A DVD player contains a laser. By moving the lens longitudinally, different depths can be reached in the disc. In order to make room for a lot of information on every disc, the beam has to be focused on as small an area as possible. This cannot be done with any other light source.

10. Which of the following is used in atomic clocks?
a) Laser
b) Quartz
c) Maser
d) Helium

View Answer

Answer: c [Reason:] Before laser maser was used. It stood for microwave amplification by stimulated emission of radiation. This was based of Albert Einstein’s principle of stimulated emission. It was used in atomic clock.

11. Which of the following can be used in vibrational analysis of structure?
a) Maser
b) Quarts
c) Electrical waves
d) Laser

View Answer

Answer: d [Reason:] Laser can be used in vibrational analysis of structure. This is because when a structure under test begins to vibrate a distinctive pattern begins to emerge.

Set 3

1. Same material is used to make a sphere, a cube and a thin circular plate and having the same mass. They are initially heated to a temperature of 3000°C. Which of these will cool fast?
a) Sphere
b) Cube
c) Plate
d) All thee will cool at the same rate

View Answer

Answer: c [Reason:] All three have the same mass and hence same volume. Therefore the plate has a maximum surface area. So, the plate will cool fastest.

2. Heat given to a body, which raises its temperature by 1°C is
a) Water equivalent
b) Temperature gradient
c) Thermal capacity
d) Specific heat

View Answer

Answer: c [Reason:] Heat required to raise the temperature of a body through 1°C is called thermal capacity

3. According to Newton’s law of cooling, the rate at which a body cools is proportional to (∆θ)n, where ∆θ is the difference if the temperature of the body and the surroundings. What is n equal to?
a) Two
b) Three
c) Four
d) One

View Answer

Answer: d [Reason:] According to Newton’s law of cooling, Rate of cooling is proportional to temperature difference between body and its surroundings Therefore, n = 1

4. If boiling point of water is 95°F, what will be reading at Celsius scale?
a) 7°C
b) 65°C
c) 63°C
d) 35°C

View Answer

Answer: d [Reason:] C = 5/9(F-32) C = 5/9(95-32) C = 35°C

5. 50g of ice at 0°C is mixed with 50g of water at 80°C, final temperature of mixture of will be
a) 0°C
b) 40°C
c) 60°C
d) 4°C

View Answer

Answer: a [Reason:] Heat required to melt 50g ice = mL = 50×80=4000cal Heat given out by water in cooling from 80°C to 0 = mc∆T=50×1×80=4000cal Heat given by water is just sufficient to melt the whole ice. So the final temperature is 0°C.

6. Assertion: Water kept in an open vessel will quickly evaporate on the surface of the moon [Reason:] The temperature at the surface of the moon is much higher than the boiling point of water
a) Both assertion and reason are true and reason is the 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 is false

View Answer

Answer: c [Reason:] The assertion is true but the reason is false. Evaporation occurs at all temperatures. Due to low gravity on moon, the escape velocity is small.

7. Assertion: In a pressure cooker the water is about to be boiled. The cooker is then removed from the stove. Now on removing the lid of the pressure cooker, the water boils again [Reason:] The impurities in water bring down its boiling point
a) Both assertion and reason are true and reason is the 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 is false

View Answer

Answer: c [Reason:] The assertion is true but the reason is false. When the lid is removed, the pressure decreases. This decreases the boiling point of water and water begins to boil.

8. The Wien’s displacement law expresses relation between
a) Wavelength corresponding to maximum energy and absolute temperature
b) Radiated energy and wavelength
c) Temperature and emissive power
d) Colour of light and emissive power

View Answer

Answer: a [Reason:] Wien’s displacement law gives relation between wavelength corresponding to maximum energy emitted by a black body and its absolute temperature.

9. Two containers A and B are partly filled with water and closed. The volume of A is twice that of B and it contains half the amount of water in B. If both are at same temperature, the water vapour in the containers will have pressure in the ratio of
a) 1:2
b) 1:1
c) 2:1
d) 4:1

View Answer

Answer: b [Reason:] Vapour pressure does not depend on the amount of the substance. It depends on temperature only.

10. The thermal capacity of 40g of aluminium (specific heat = 0.2 cal°g-1 C-1) is
a) 40cal°C-1
b) 160 cal°C-1
c) 200 cal°C-1
d) 8 cal°C-1

View Answer

Answer: d [Reason:] Thermal capacity = mc Thermal capacity = 40g×0.2cal g-1 C-1 = 80 cal°C-1

11. 80g of water at 30°C is poured on a large block of ice which is at 0°C. The mass of ice that melts is
a) 30g
b) 80g
c) 150g
d) 1600g

View Answer

Answer: a [Reason:] Heat used in melting m gram of ice = Heat lost by 80g water mL=80×1×30 m=(80×1×30)/80=30g

12. A constant volume gas thermometer using helium records a pressure of 20.0kPa at the triple point of water and pressure of 14.3 kPa at the temperature of ‘dry ice’. What is the temperature of dry ice?
a) 19.530K
b) 1.9530K
c) 195.30K
d) 1953.0K

View Answer

Answer: c [Reason:] Temperature of dry ice, T=P/Ptr ×Ttr=(14.3×273.16)/20 Temperature = 195.30K

Set 4

1. Which of the following is true about the universe?
a) It is an open system
b) It is a closed system
c) It is an isolated system
d) It is an international system

View Answer

Answer: c [Reason:] In spite of all the violent phenomenon occurring in this universe all the time, the total energy if the universe remains constant. The total energy remains constant only in an isolated system. Thus universe is an example of an isolated system.

2. Which of the following holds good in all natural processes?
a) The Doppler Effect
b) Newton’s law of gravitation
c) Electromagnetic law
d) Lenz’s law

View Answer

Answer: b [Reason:] It states that every body in the universe is attracted to every other body with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them. Hence it holds good in all natural processes.

3. Strong nuclear force is independent of charge. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] Nuclear forces between a proton and proton, a neutron and neutron are nearly equally strong. This indicated that the strong nuclear force does not depend on the charge on the charge of the nucleons.

4. Which of the following leads to law of conservation of energy?
a) Gravity
b) Isotropy
c) Nuclear force
d) Homogeneity of time

View Answer

Answer: d [Reason:] If we perform an experiment at a certain place today and repeat it after one yer at the same place, we obtain the same results. This symmetry of nature with respect to translation or displacement of time is called homogeneity of time and it leads to law of conservation of energy.

5. Which of the following leads to law of conservation of angular momentum?
a) Isotropy of space
b) Homogeneity of time
c) Nuclear force
d) Gravity

View Answer

Answer: a [Reason:] Law of nature take the same form everywhere in the universe. That is there is no particular location in the universe. This symmetry of the laws of nature with respect to translation in space id called homogeneity of space and gives rise to the law of conservation of linear momentum.

6. Which of the following is the SI unit of luminous intensity?
a) Sterdian
b) Radian
c) Mole
d) Candela

View Answer

Answer: d [Reason:] Candela is the SI unit of luminous intensity. One candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity of 1/683 watt per sterdian in that direction.

7. Sterdian is the SI unit of which of the following?
a) Phase angle
b) Luminous intensity
c) Mass
d) Solid angle

View Answer

Answer: d [Reason:] Sterdian is defined as the solid angle subtended at the centre of sphere by a surface of the sphere equal in area to that of a square, having each side equal to the radius of the sphere.

8. How many light years are there in one metre?
a) 9.46×1015ly
b) 1.057×10-16ly
c) 1ly
d) 1×10-16ly

View Answer

Answer: b [Reason:] 1 light year = 9.46×1015m 1m = 1/(9.46×1015 )ly = 1.057×10-16ly

9. The radius of gold nucleus is 41.3fermi. Express its volume in m3.
a) 41.3×10-15 m3
b) 2.95×10-40 m3
c) 4.19 m3
d) 29.33 m3

View Answer

Answer: b [Reason:] Radius = 41.3 Fermi = 41.3×10-15m V = 4/3 πr3 = 2.95×10-40 m3

10. Convert an acceleration of 2km/h2 into cm/s2.
a) 2×105 cm/s2
b) 0.0027 cm/s2
c) 0.0154 cm/s2
d) 0.055 cm/s2

View Answer

Answer: c [Reason:] a = 2 km/h2 a = 0.0154 cm/s2

Set 5

1. A ship of mass 3×107kg initially at rest is pulled by a force of 5×104N through a distance of 3m. Assuming that the resistance due to water is negligible, the speed of the ship is
a) 1.5m/s
b) 60m/s
c) 0.1m/s
d) 5m/s

View Answer

Answer: c [Reason:] a = F/m = (5×104)/(3×107 ) Speed attained by the ship, v = √2as = 0.1m/s

2. When a bicycle is in motion, the force of friction exerted by ground on the two wheels is such that, it acts
a) In the backward direction on the front wheel and in the backward direction on the rear wheel
b) In the forward direction on the front wheel and in the backward direction on the rear wheel
c) In the backward direction on both front and the back wheel
d) In the forward direction in both front and the back wheel

View Answer

Answer: a [Reason:] When a bicycle is in motion, the force of friction acts in the backward direction on the front wheel and in the forward direction on the rear wheel.

3. A weight W rests on a rough horizontal plane. If the angle of friction is θ, the least force that will move the body along the plane will be
a) W cosθ
b) W tanθ
c) W cotθ
d) W sinθ

View Answer

Answer: b [Reason:] The least force required to move weight W on a horizontal plane is equal to the force of friction, f=μR=μmg or f= W tanθ

4. Statement 1- A cloth covers a table. Some dishes are kept on it. The cloth can be pulled out without dislodging the dishes from the table
Statement 2- For every action, there is an equal and opposite reaction.
a) Statement 2 is correct explanation for statement 1
b) Statement 2 is not correct explanation for statement 1
c) Statement 1 is true but statement 2 is false
d) Statement 1 is false but statement 2 is true

View Answer

Answer: b [Reason:] The dishes will remain on the table due to inertia of rest and not due to action-reaction forces. Statement 2 is not the correct explanation of statement 1.

5. A player caught a cricket ball of mass 150g moving at a rate of 20m/s. If the ball catching process is completed in 0.1s, the force on the blow exerted by the ball on the hand of the player is equal to
a) 30N
b) 300N
c) 150N
d) 3N

View Answer

Answer: a [Reason:] Impulse = change in momentum F = (m(v-u))/t = -30N

6. A machine gun fires a bullet of mass 40g with a velocity of 1200m/s =. The man holding it, can exert a maximum force of 144N on the gun. How many bullets can he fire per second at the most?
a) One
b) Four
c) Two
d) Three

View Answer

Answer: d [Reason:] Let the maximum number of bullets than can be fired per second be n Change in momentum of n bullets = nm(v-u) = n×(40(1200-0))/1000 =48n kgm/s As impulse = Change in momentum Ft = 48n n = Ft/48 = 3bullets/second

7. A light spring balance hangs from hook of the other spring balance and a block of mass Mkg hangs from the former one. Then, the true statement is
a) Both the scales read Mkg each
b) The scale of the lower one reads Mkg and of the upper one zero
c) The reading of the two scales can be anything but the sum of the readings will be Mkg
d) Both the scales read M/2 kg

View Answer

Answer: a [Reason:] As the suspended spring balance is lighter one, both the scales will read Mkg each.

8. A particle is acted upon by a force of constant magnitude which is always perpendicular to the velocity of the particle. The motion of the particle takes place in a plane. It follows that
a) Its velocity is constant
b) Its acceleration is constant
c) Its kinetic energy is constant
d) It moves in a straight line

View Answer

Answer: c [Reason:] It is a case of uniform motion in which velocity and acceleration vectors change due to change in direction. As the magnitude of velocity remains constant, the kinetic energy is constant.

9. A student unable to answer a question on Newton’s law of motion attempts to pull himself up by tugging on his hair. He will not succeed
a) As the force exerted is small
b) The frictional force while gripping, is small
c) Newton’s law of inertia is not applicable to living beings
d) As the force applied is internal to the system

View Answer

Answer: d [Reason:] The force applied by the student into himself is an internal force. According to Newton’s law, only an external force can change the state of motion of an object.

10. A man of mass 60 kg and a boy of mass 30 kg are standing together on frictionless ice surface. If they push each other apart, the man moves away with a speed of 0.4m/s relative to ice. After 5s they will be away from each other at a distance of
a) 9 m
b) 3 m
c) 6 m
d) 30 m

View Answer

Answer: c [Reason:] Momentum of man = -Momentum of boy 60×0.4 = -30×v Velocity of the boy = -0.8m/s Relative velocity = 0.4+0.8 = 1.2m/s Distance between man and boy after 5s = 1.2×5 = 6 m