When thermal conductivity is said to be constant ?

The unit of thermal conductivity is:

In an 20 m deep lake, the bottom is at a constant temperature of 4^(@)C . The air temperature is constant at -10 ^(@)C . The thermal conductivity of ice in 4 times that water. Neglecting the expansion of water on freezing, the maximum thickness of ice will be

On which fcator does the thermal conductivity depend ?

Statement I: Two solid cylindrical rods of identical size and different thermal conductivity K_1 and K_2 are connected in series. Then the equivalent thermal conductivity of two rods system is less than that value of thermal conductivity of either rod. Statement II: For two cylindrical rods of identical size and different thermal conductivity K_1 and K_2 connected in series, the equivalent thermal conductivity K is given by (2)/(K)=(1)/(K_1)+(1)/(K_2)

The ends Q and R of two thin wires, PQ and RS, are soldered (joined) together. Initially each of the of wire has a length of 1m at 10^@C. Now the end P is maintained at 10^@C, while the ends S is heated and maintained at 400^@C. The system is thermally insultated from its surroundings. If the thermal conductivity of wire PQ is twice that of the wire RS and the coefficient of linear thermal expansion of PQ is 1.2xx10^-5K^-1, the change in length of the wire PQ is

Assertion : At same temperature among plastic body of pen and metal portion on cap, metal portion is cold. Reason : Thermal conductivity of metal is more than plastic.

A cylindrical block of length 0.4 m and area of cross-section 0.04 m^2 is placed coaxially on a thin metal disc of mass 0.4 kg and of the same cross - section. The upper face of the cylinder is maintained at a constant temperature of 400 K and the initial temperature of the disc is 300K . if the thermal conductivity of the material of the cylinder is 10 "watt"// m.K and the specific heat of the material of the disc is 600J//kg.K , how long will it take for the temperature of the disc to increase to 350 K ? Assume for purpose of calculation the thermal conductivity of the disc to be very high and the system to be thermally insulated except for the upper face of the cylinder.

A rod of length L with sides fully insulated is made of a material whose thermal conductivity K varies with temperature as K=(alpha)/(T) where alpha is constant. The ends of rod are at temperature T_(1) and T_(2)(T_(2)gtT_(1)) Find the rate of heat flow per unit area of rod .

Statement- 1 : High thermal conductivity of metals is due to presence of free electrons. Statement- 2 : Electrons at same temperature have very high average velocity than atoms.

Consider a compound slab consisting of two different materials having equal thicknesses and thermal conductivities K and 2K respectively. The equivalent thermal conductivity of the slab is . . . . . .. .