Five rods of same dimensions are arranged as shown in the figure. They have thermal conductivities k₁, k₂, k₃, k₄ and k₅ when points A and B are maintained at different temperatures. No heat flows through the central rod if

• k₁k₄ = k₂k₃

• k₁ = k₄ and k₂ = k₃

• $\frac{{\mathrm{k}}_1}{{\mathrm{k}}_4} = \frac{{\mathrm{k}}_2}{{\mathrm{k}}_3}$

• k₁k₂ = k₃k₄

82.

The charge following through a resistance R varies with time t as Q = at - bt², where a and b are positive constants. The total heat produced in R is,

• a³R/3b

• a³R/2b

• a³R/b

• a³R/b

Coefficient of linear expansion of brass and steel rods are  and . Lengths of brass and steel rods are l₁ and l₂ respectively. If (I₂ - I₁) is maintained same at all temperatures, which one of the following relations holds good?

The two ends of a metal rod are maintained at temperatures 100^o C and 110^o C. The rate of heat flow in the rod is found to be 4.0 J/s. If the ends are maintained at temperatures 200^o C and 210^o C, the rate of heat flow will be

• 44.0 J/s

• 16.8 J/s

• 8.0 J/s

• 8.0 J/s

One mole of an ideal diatomic gas undergoes a transition from A to B along a path AB as shown in the figure.


The change in internal energy of the gas during the transition is 

• 20 kJ

• -20 kJ

• 20 J

• 20 J

A slab of stone of area of 0.36 m² and thickness 0.1 m is exposed on the lower surface to steam at 100^oC. A block of ice at 0^o C rests on the upper surface of the slab. In one hour 4.8 kg of ice is melted. The thermal conductivity of slab is
(Given latent heat of fusion of ice = 3.36 x 10⁵ J Kg^-1)

• 1.24 J/m/s/^oC

• 1.29 J/m/s^oC

• 2.05 J/m/s^o C

• 2.05 J/m/s^o C

An ideal gas goes from state A to state B via three different processes as indicated in the p-V diagram.



If Q₁, Q₂, Q₃ indicate the heat absorbed by the gas along the three processes and ΔU₁, ΔU₂, ΔU₃ indicate the change in internal energy along the three processes respectively, then

• Q₁> Q₂> Q₃ and ΔU₁=ΔU₂= ΔU₃ 

• Q₃> Q₂> Q₁ and ΔU₁=ΔU₂= ΔU₃ 

• Q₁= Q₂= Q₃ and ΔU₁=ΔU₂= ΔU₃ 

• Q₁= Q₂= Q₃ and ΔU₁=ΔU₂= ΔU₃ 

If the radius of a star is  R and it acts as a black body, what would be the temperature of the star, in which the rate of energy production is Q?

• Q/4πR²σ

• (Q/4πR²σ)^-1/2

• (4πR²Q/σ)^1/4

• (4πR²Q/σ)^1/4

Liquid oxygen at 50  K is heated to 3000 K at a constant pressure of 1 atm. The rate of heating is constant. which one of the following graphs represents the variation of temperature with time?

The piece of iron is heated in a flame. If first becomes dull red then becomes reddish yellow and finally turns to white hot. The correct explanation for the above observation is possible by using,

• Stefan's law

• Wien's displacement law

• Kirchoff's law

• Kirchoff's law