Two Slabs A and B of Different Materials But Of The Same Thickness Are Joined As Shown In Fig. 8.8. The Thermal Conductivities Of A and B are k1and k2 respectively. The Thermal Conductivity Of The Composite Slab Will Be                                                                  

The equation of state of n moles of an ideal gas is PV = nRT, where R is a constant. The SI unit for R is

A thin copper wire of length L increases its length by 1% when heated from temperature T₁ to T₂. What is the percentage change in area when a thin copper plate having dimensions  is heated from T₁ toT₂?

In Fig., curves AB and CD represent the relation between pressure P and volume V of an ideal gas. One of the curves represents an isothermal expansion and the other represents an adiabatic expansion. Which curve represents an adiabatic expansion?

One mole of an ideal gas  at absolute temperature T₁ is adiabatically compressed from an initial pressure P₁ to a final pressure P₂. The resulting temperatureT₂ of the gas is given by

A certain mass of an ideal gas at pressure P₁ is adiabatically expanded from an initial volume V₁ to a final volume V₂. The resulting pressure P₂ of the gas is given by

A Carnot’s engine working between 27^oC and 127^oC takes up 800 J of heat from the reservoir in one cycle. What is the work done by the engine?

A Carnot’s engine whose sink is at a temperature of 300 K has an efficiency of 40%. By how much should the temperature of the source be increased so as to increase the efficiency to 60%?

The surface of the earth receives solar radiation at the rate of 1400 Wm ^{– 2}. The distance of the centre of the sun from the surface of the earth is  m and the radius of the sun is  m. Treating the sun as a back body, it follows from the above data that the surface temperature of the sun is about

What is the SI unit of the Boltzmann’s constant?

A composite slap consists of two slabs A and B of different materials but of the same thickness placed one on top of the other. The thermal conductivities of A and B are k₁ and k₂ respectively. A steady temperature difference of 12^oC is maintained across the composite slab. If k₁ = k₂/2, the temperature difference across slab A will be