UPSC General Science : Heat and Thermodynamics Notes Part 1

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Today’s Topic: Heat and Thermodynamics

Q1. According to Kepler’s law of planetary motion, the square of planets is proportional to:

a) The cube of their mean distances from the sun.

b) The mean distance from the sun

c) The square of their distances from the sun.

d) None of the above.

Ans:     A

Explanation:    Kepler formulated that three basic laws of planetary motion:

1) Every planet moves in an elliptical orbits with the sun bring at one of its face.

2) The radius vector drawn from the sun to the planets sweep out equal areas in equal intervals of time.

3) The square of the time period of revolution of a planet around the sun proportional to the cube of semi major axis of the orbit.

Q2. Which one of the following is not property of Radiants heat:

a) Radiant heat does not obey the law of Reflection.

b) Radiant heat can be transmitted through vacuum.

c) Radiant heat transmitted in straight line.

d) None of these.

Ans:    A

Explanation:    The Radiant heat obey the laws of reflection using a thermopile, we can detect that the reflected heat radiation from a plane polished surface obey the law of a plane polished surface obey the law of Reflection (i.e. the angle of incidence is equal to the angle of Reflection. The incidence heat radiation, the reflect heat radiation and the normal to the polished surface at the point of incidence are in the same).

Q3. A rocket works on which one of the following:

a) Conservation of angular momentum

b) Conservation of mass

c) Conservation of energy

d) Conservation of linear momentum

Ans:    D

Explanation:    A rocket works on conservation of linear momentum. The operation of a rocket illustrates the conservation of linear momentum. Just before launching of linear momentum of rocket is zero. When rocket fired, it forces a jet of hot gasses with a velocity through nozzle. The jet of gases acquires a momentum downward. Hence, the rocket acquires a momentum of equal magnitude in opposite direction and then rocket moves upward.

Q4. Consider the following statements and select the correct code:

1) Ice is a bad conductor of heat.

2) The volume of water is minimum at 40C.

3) If the expansion of water had not been anomalous, the ponds and lakes would have frozen from top to bottom and all the animal living in water would have died.

a) All 1, 2 and 3 are correct

b) Only 2 and 3 are correct

c) 3 and 1 are correct

d) 1 and 2

Ans:     A

Explanation:    On being cooled, water contract upto 40°C. If it is further cooled, it begins to expand instead of contracting. In winter the water on the upper surface of the ponds and the lakes freezes, but below the frozen layer water remain at 40°C which has maximum density. The surface layer being lighter, float on it. The aquatic animals can live in water 40°C below the frozen layer.

Q5. Ball pen functions on which one of the following principle of physics:

a) Surface tension

b) Viscosity

c) Gravitational

d) None of these

Ans:     A

Explanation:    The ball pen functions on the principle of capillarity and surface tension. Rise of oil in the wicks of the oil lamps, rise of sap in plants, rise of ink in the narrow slit of the pen and soaking up of ink in the blotting paper are all example of capillarity.

Q6. The general rule is that when liquid solidifies its volume decreases and when solids liquefies, its volume increases. Which one of the following when converted into liquid decreases in volume:

a) Brass

b) Ice

c) Wrought Iron

d) All the above.

Ans:     D

Explanation:    When wrought iron, ice, brass etc. Are converted into liquid their volume decreases. Ice is seen to fleet of water. This mean that the volume of the given mass of ice is greater than the volume of some mass of water.

Q7. Which one of the following substances has the highest heat capacity:

a) Ice

b) Paraffin

c) Water

d) None of these.

Ans      C


Specific heat capacity of water           =          4200J/kg C,

Specific heat capacity of paraffin        =          220J/kg C,

Specific heat capacity of Ice                =          2108J/kg C,

Specific heat capacity of glycerine      =          2436J/kg C.

In the given option water has highest specific heat capacity.

Q8. Consider the following statements and select the correct code:

1) The high temperature of sun and stars are sufficient to bring about the fusion of hydrogen nuclei to form nuclear. Helium with tremendous release of energy.

2) Carbon acts as a catalyst for this reaction.

a) Only 2 is correct

b) Only 1 is correct

c) Both 1 and 2 are incorrect

d) Both 1 and 2 are correct

Ans:     D

Explanation:    For the hydrogen atom fuse together in the presence of carbon, which acts as a catalyst give one atom of helium with little loss mass of and release of energy.

Q9. Weightlessness experienced while orbiting the earth is a result of which of the following:

1) Acceleration

2) Zero gravity

3) Centre of gravity

4) No result.


a) 1 and 2

b) 2 and 3

c) Only 4

d) Only 1

Ans:     D

Explanation:    When a object / person in spaceship is orbiting the earth, the necessary centripetal acceleration provided by acceleration due to gravity (g).

Q10. Which one of the following would hold true, if a gymnast sitting on a rotating stool, with his/her arms outstretched, suddenly lower her/his arms:

a) Angular velocity remain constant

b) The angular momentum decreases.

c) The angular momentum increases

d) Moment of inter tie decreases.

Ans:     D

Explanation:    For the above condition the moment of inertia of gymnast decreases but the momentum of the body is remain constant. The angular velocity of the body is increases not remain constant.