Question

Heat current is maximum in which of the following (rods are of identical dimension)
A. Copper
B. Copper steel
C. Steel copper
D. Steel

Answer 1

Hint: Thermal conductivity is a measure of the capacity of a substance to conduct heat. Low thermal conductivity materials will transmit heat at a slower pace than high thermal conductivity materials. Metals that have high thermal conductivity are extremely effective at transferring heat, whereas insulating materials have low thermal conductivity. These high thermal conductivity materials are commonly utilized in heat sink applications, where low thermal conductivity materials are used as thermal insulation.

Complete step by step solution:
As we know the formula for the heat current, as,
\[\dfrac{{dQ}}{{dt}} \propto K\]
That is, the rate of change of heat is directly proportional to the thermal conductivity. As the thermal conductivity of copper is found to be maximum, then, the heat current will also be maximum in copper. The thermal resistance of copper is lesser than the thermal resistance of steel.

The thermal conductivities of typical materials range from 4-8 orders of magnitude. Pure metals have high thermal conductivity, whereas gases have low thermal conductivity. For example, copper has a heat conductivity of 10K times that of air under normal circumstances.

And also, the allotropes of carbon, namely graphite and diamond have the greatest thermal conductivities at room temperature. Therefore, the thermal resistance is minimum so heat current is maximum in copper.

Hence, option A is the correct answer.

Note:Lattice vibrations are the reasons for thermal conductivity in non-metals. The fluctuation in temperature (increase or decrease) does not significantly affect the mean free path of phonons, which means that the variation in thermal conductivities of non-metals is minimal.