Question

A coin is dipped in the molten wax in a glass tube. When we heat the upper part of the glass tube, the wax around the coil will not melt because:
(A) Wax has a very high melting point
(B) Was is a good conductor of heat
(C) Glass is a good conductor of heat
(D) Wax or glass are bad conductors of heat

Answer 1

For the wax with the coin to melt, the temperature must also reach the melting point of the wax. The temperature will increase depending on how fast the heat at the top gets to the wax at the bottom.

Complete step by step answer:
When the coin is dropped in the glass tube, it drops to the bottom of the tube. The wax solidifies around the coin. Now, we are told that the upper part of the glass tube is being heated, and the wax around the coil (which is at the bottom part of the glass tube) will not melt. We are to identify the reason why this is so.
Generally, for the wax around the coin to melt, the heat applied to the upper part of the glass tube needs to be transferred to the lower part of the glass tube, then conducted to the wax around the coin through the wax closer to the class tube.
Hence, if the wax around the coin does not melt, it means either one of these things is not happening or it’s not happening fast enough. This rate of transfer of heat from one part of a body to another is the conductivity of the material. Hence, either the conductivity of glass is poor or the conductivity of wax is poor.
The correct option is, then, D.

Note
In actuality, both glass and wax are poor conductors of heat. Also, being a poor conductor of heat is not the entire requirement for the wax around the coin to not melt. The heat lost to the surrounding must occur faster than the conductivity. If there is no heat lost to the surrounding for an example, it may take long, but the wax will inevitably melt.