Question

On a cold morning, a metal surface in touching is felt colder than a wooden surface, because the metal has:
A. low thermal conductivity
B. high thermal conductivity
C. high specific heat
D. low specific heat

Answer 1

Hint:The temperature experienced by a human body is nothing but the rate of heat transfer that takes place due to contact with other bodies. The mechanism of heat transfer through a solid is called Conduction. It is a process in which heat is transferred from one particle to another without dislocation of the particle from their equilibrium position. In this process transfer can be represented on an atomic scale as an exchange of kinetic energy between microscopic particles. A property of material called the thermal conductivity of the material plays an eminent role in it.

Complete answer:
 Metal surface feels colder in touching because it has a higher Thermal conductivity.
Explanation: Heat transfer in conduction is governed by following equation
$Q = - KA\dfrac{{dT}}{{dx}}$
\[K = \] Thermal conductivity of material,
$A = $ Cross-sectional area,
$\dfrac{{dT}}{{dx}} = $ Temperature gradient.

From the equation one can see that higher the value of thermal conductivity, higher will be the value of heat transfer, since metals have a higher value of thermal conductivity as compared to that of wood (practically an insulator), the rate of heat transfer through metal is higher. So to maintain a steady state, heat from our body passes through a conductor at a faster rate and hence we experience a metal surface to be colder at the same environmental temperature compared to a wooden surface.

Thus we can say that the metal surface feels colder in touch because it has a higher thermal conductivity.

Therefore option B is the correct answer.

Note:In the problem we have specific heat as an option which could create confusion, one must remember that the specific heat does not tell the rate of heat transfer through a body, but it is the amount of heat required to increase temperature of a unit mass system by unit Kelvin.