Thermal Propert...

A and B are two points on a uniform metal ring whose centre is O. The angle AOB = $$\theta$$. A angle B are maintained at two different constant temperatures. When $$\theta = 180^o$$, the rate of total heat flow from A to B is $$1.2 W$$. When $$\theta = 90^o$$ then this rate will be

With cold wind keeping the surface at $$20^oC$$ a layer of ice on a pond grows in thickness from 20 mm to 21 mm in 10 min. Later with the surface at the same temperature it will grow from 40 mm to 42 mm in approximately

A refrigerator is thermally equivalent to a box of cork board 90$$\mathrm { mm }$$ thick and $$\mathrm { m } ^ { 2 }$$ in inner surface area, the thermal conductivity of cork being 0.05$$\mathrm { W } / \mathrm { mK }$$ . The motor of the refrigerator runs 15$$\%$$ of the time while the door closed. The inside wall of the door, when it is closed,is kept, on an average, $$22 ^ { \circ } \mathrm { C }$$ below the temperature of the outside wall. The rate at which heat is taken from the interior wall while the motor is running is

The thermal radiation from a hot body travels with a speed of

A body cools from $$62^{\circ}$$   C  to   $$50^{\circ}$$C  in 10 minutes and then to $$42^{\circ}$$ C in next 10 minutes.  The temperature of surrounding is : 

Water standing in the open at $$32^0C$$ evaporates because of the escape of some of the surface molecules. The heat of vaporization ($$540 cal/g$$) is approximately equal to $$\epsilon$$n, where $$\epsilon$$ is the average energy of the escaping molecules and n is the number of molecules per gram. The value of $$\epsilon$$ is close to

A 20gm bullet whose specific heat is 5000 J/ (kg- $$^o C$$) and moving at 2000 m/s plunges into a 1.0 kg block of wax whose specific heat is 3000 J/(kg- $$^o C$$). Both bullet and wax are $$25^o C$$ and assume that (i) the bullet comes to rest in the wax and (ii) all its kinetic energy goes into heating the wax.  Thermal temperature of the wax in $$^o C$$ is close to

On a hypothetical scale  $$A$$  the ice point is  $$42 ^ { \circ }$$  and the steam points is  $$182 ^ { \circ }$$  For another scale   $$B,$$  the ice point is  $$- 10 ^ { \circ }$$  and steam point is  $$90 ^ { \circ } $$  If  $$B$$  reads  $$60 ^ { \circ } ,$$  the reading of  $$A$$  is,

Two spheres of the same material havethe same radius but one is hollow while the other is solid. Both spheres are heated to same temperature. Then

Two identical rods of a metal are welded as shown in figure (a). A certain amount of heat flows through them in 12 min. If the rods are welded as shown in figure (b) then the same amount of heat will flow in