Answers to Review Questions: Ch # 11 Heat

Karachi Board ( BSEK)

Q.11.1How do you distinguish between temperature and heat?give examples.

Ans.Heat is the total kinetic energy of molecules of a body.But temperature is the average kinetic energy of the molecules of a body.If we dip a red hot iron ball in the sea ,heat will flow from the ball to water (from high to low temperature),although the amount of heat possessed by the ball is very small as compared to the grater amount of heat contained by the sea.

Q.11.2Why earth is not in the thermal equilibrium with the sun?

Ans.The earth is not in thermal equilibrium with the sun because while the earth is being warmed by the absorbed energy it is also loosing heat in various ways .Which includes conduction, convection and radiation.

Q.11.3 Is temperature is the macroscopic concept?

 Ans. Yes, temperature is the macroscopic quantity.

Q.11.4 It is observed that when………….. then rises.Explain

Ans.When mercury in glass thermometer is put in a flame ,the glass bulb expands. so the column of mercury descends. but no sooner the heat reaches the mercury in the bulb ,it expands; and the expansion is grater than the glass bulb. so now, the mercury rises in the column.

Q.11.5 Is it correct that unit for specific heat capacity is m²s^-2 C^-1

Ans.Yes it is correct .because c=ΔQ / mΔT

The SI unit of c = J/ kg C = N.m/kg C = kg m/ s² m/kg C

And which is equal to m²s^-2 C^-1

Q.11.6 What is standard temperature?

Ans.The standard temperature is ice point , i.e. 273 K

Q.11.7 When a block with a hole…….. make it small ?

Ans.Thermal expansion of homogeneous substances causes increase in all directions with the same linear thermal expansion co-efficient. This increase in all directions causes an effective magnification of an object. so the hole will expand outward.

Q.11.8 A thermometer ….. something else?

Ans. This thermometer will record the temperature of the surrounding.

Q.11.9 Will one kilogram……..explain.

Ans.Yes, one kilogram of hydrogen will contain more atoms than one kilogram of lead,because hydrogen atoms are much more lighter than lead atoms.

Q.11.10 The Pressure…….. Why ?

Ans.This is so because the hydrogen molecules are lighter than oxygen molecules.Molecular speed is inversely proportional to the molecular mass.Hence hydrogen will leak more quickly than oxygen.

Q.11.11 What are some factors that affect the efficiency of auto mobile engines.

Ans. It depends upon (i) Temperature of hot reservoir (ii) temperature of cold reservoir

(iii) Heat losses

Q.11.12 What happens ……. Of the room?

Ans. Heat is removed from the room by air conditioner but heat is released on the other side. Thus, the room cannot be cooled by running a air conditioner in the middle of the room.

Q.11.13 When a sealed….. of the coffee.

Ans.(a) The temperature of the coffee increases due to shaking

        (b) Th internal energy of coffee increases.