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NEET UG PHYSICS MCQ: THERMAL PROPERTIES OF MATTER

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200 cal of heat is given, whose efficiency is 40 %, takes is heat from a source maintained at a temperature of 500 K. It is desired to have an engine of efficiency 60 % Then, the intake temperature for the same exhaust (sink). Temperature must be

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Correct option: A

Efficiency of carnot engine cannot be made larger than 50 %

Efficiency of carnot engine cannot be made larger than 50 % is the correct answer because if the efficiency is 40% with a source at 500K, then the sink temperature is 300K. With this sink temperature, an efficiency of 60% would require a source temperature of 750K. However, the problem states that 200 cal of heat is given, whose efficiency is 40 %, takes is heat from a source maintained at a temperature of 500 K. It is desired to have an engine of efficiency 60 % Then, the intake temperature for the same exhaust (sink). Temperature must be

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Four identical calorimeters painted in different colours, are heated to same temperature and then allowed to cool in vacuum. Which will cool fastest? An ice cube of dimensions

60 \mathrm{~cm} \times 50 \mathrm{~cm} \times 20 \mathrm{~cm}

is placed in an insulation box of wall thickness

1 \mathrm{~cm}

. The box keeping the ice cube at

0^{\circ} \mathrm{C}

of temperature is brought to a room of temperature

40^{\circ} \mathrm{C}

. The rate of melting of ice is approximately.

(Latent heat of fusion of ice is

3.4 \times 10^5 \mathrm{~J} \mathrm{~kg}^{-1}

and thermal conducting of insulation wall is

\left. {0.05{\text{W}}{{\text{m}}^{ - 1}}^\circ {{\text{C}}^{ - 1}}} \right)

A black body radiates heat energy at the rate of

2 \times 10^5 \mathrm{~J} / \mathrm{sm}^2

127^{\circ} \mathrm{C}

. The temp of black body at which rate becomes

32 \times 10^5 \mathrm{~J} / \mathrm{s}-\mathrm{m}^2

is: The amount of radiation emitted by a perfectly black body is proportional to Amount of heat required to raise the temperature of a body through 1K is called its If Poisson’s ratio

\sigma

+ \frac{1}{2}

for a material, then the material is