MEDIUM
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Is steel is a good conductor of heat?

Important Questions on Thermal Properties of Matter

MEDIUM
A cylinder of radius R is surrounded by a cylindrical shell of inner radius R and outer radius 2R. The thermal conductivity of the material of the inner cylinder is K1 and that of the outer cylinder is K2. Assuming no loss of heat, the effective thermal conductivity of the system for heat flowing along the length of the cylinder is:
EASY
The two ends of a metal rod are maintained at temperatures 100 °C and 110 °C . The rate of heat flow in the rod is found to be 4.0 J s-1 . If the ends are maintained at temperatures 200 °C and 210 °C , the rate of heat flow will be:
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A metallic prong consists of 4 rods made of the same material, cross-section, and same lengths as shown.

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The three forked ends are kept at 100oC and the handle end is at 0oC. The temperature of the junction is

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Two materials having coefficients of thermal conductivity 3K and K and thickness d and 3d respectively, are joined to form a slab as shown in the figure. The temperatures of the outer surfaces are θ2 and θ1 respectively, θ2>θ1. The temperature at the interface is
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EASY
State whether the following statement is true or false:
“The constituent particles of a material change position during conduction of heat through it.”
HARD
Three rods of Copper, Brass and Steel are welded together to form a Y-shaped structure. Area of cross-section of each rod is 4 cm2. End of copper rod is maintained at 100°C. Where as ends of brass and steel are kept at 0°C. Lengths of the copper, brass and steel rods are 46, 13 and 12 cms respectively. The rods are thermally insulated from surroundings except at ends. Thermal conductivities of copper, brass and steel are 0.92, 0.26 and 0.12 CGS units respectively. Rate of heat flow through copper rod is :
MEDIUM
Solar energy is incident normally on the earth's surface at the rate of about 1.4 kW m-2 . The distance between the earth and the sun is 1.5×1011 m . Energy E and mass m are related by the Einstein equation, E=mc2 where c=3×108 m s-1 is the speed of light in free space. The decrease in the mass of the sun is
MEDIUM

Consider a ball of mass 100 g attached to one end of a spring k=800 N m-1 and immersed in 0.5 kg water. Assume the complete system is in thermal equilibrium. The spring is now stretched to 20 cm and the mass is released so that it vibrates up and down. Estimate the change in temperature of water before the vibrations stop.

(Specific heat of the material of the ball =400 J kg-1 K-1 and Specific heat of water =4200 J kg-1 K-1)

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As per the given figure, two plates A and B of thermal conductivity K and 2K are joined together to form a compound plate. The thickness of plates are 4.0 cm and 2.5 cm respectively and the area of cross-section is 120 cm2 for each plate. The equivalent thermal conductivity of the compound plate is 1+5αK, then the value of α will be _____ .

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EASY

If K1 and K2 are the thermal conductivities L1 and L2 are the lengths and A1 and A2 are the cross sectional areas of steel and copper rods respectively such that K2K1=9,A1A2=2,L1L2=2. Then, for the arrangement as shown in the figure. The value of temperature T of the steel - copper junction in the steady state will be

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MEDIUM

Three rods of identical cross-section and length are made of three different materials of thermal conductivity K1, K2 and K3, respectively. They are joined together at their ends to make a long rod (see figure). One end of the long rod is maintained at 100°C and the other at 0°C (see figure). If the joints of the rod are at 70°C and 20°C in steady and there is no loss of energy from the surface of the rod, the correct relationship between K1, K2 and K3 is :

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EASY
Cloudy nights are usually warmer than clear ones, because clouds 
HARD

Consider a pair of insulating blocks with thermal resistances R1, and R2 as shown in the figure. The temperature θ at the boundary between the two blocks is

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EASY

Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are K1 and K2. The thermal conductivity of the composite rod will be

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EASY
Three rods of identical cross-sectional area and made from the same metal, form the sides of an isosceles triangle ABC right angled at B as shown in figure. The point A and B are maintained at temperature T and 2T respectively, in the steady state. Now, assuming that only heat conduction takes place. The temperature of point C will be
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HARD
In steady state heat conduction, the equations that determine the heat current jr [heat flowing per unit time per unit area] and temperature Tr in space are exactly the same as those governing the electric field Er and electrostatic potential Vr with the equivalence given in the table below.
Heat flow Electrostatics
Tr Vr
jr Er
We exploit this equivalence to predict the rate Q of total heat flowing by conduction from the surfaces of spheres of varying radii, all maintained at the same temperature. If QRn, where R is the radius, then the value of n is
EASY

Statement A: Convection involves flow of matter within a fluid due to unequal temperatures of its parts.

Statement B: A hot bar placed under a running tap water loses heat due to effect of convection within water.

Statement.C: Heat transfer always involves temperature difference between two systems.

HARD

A thin piece of thermal conductor of constant thermal conductivity insulated on the lateral sides connects two reservoirs which are maintained at temperatures, T1 and, T2 as shown. Assuming that the system is in steady-state, which of the following plots best represents the dependence of the rate of change of entropy on the ratio of temperatures, T1T2

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MEDIUM

What is thermal conductivity? What is its SI unit?