Question

A hot metal plate is placed near to a cold metal plate. Infra-red radiation transfers thermal energy between the two plates.
Which choice of colour causes the temperature of the cold plate to increase most slowly?

(a)A
(b)B
(c)C
(d) D

Answer 1

In order to know which colour causes the temperature of the cold plate to increase most slowly, we need to use the concept of radiation of heat. We should know that white colour is a bad emitter of heat and black colour is a bad reflector. Hence, we can use this fact

Step solution There are some points to be noted:
-Shiny white is a very bad emitter of heat.
-Shiny white is a very good reflector.
So, this combination will keep the temperature of the cold plate at least.

Thus, the correct answer to this question is option (d).

Additional Information: Radiation is a method of heat transfer that does not rely upon any contact between the heat source and the heated object as is the case with conduction and convection. Heat can be transmitted through empty space by thermal radiation often called infrared radiation. This is a type of electromagnetic radiation. No mass is exchanged and no medium is required in the process of radiation. Examples of radiation is the heat from the sun, or heat released from the filament of a light bulb.

Note: While solving this question, one should be familiar with the concept of radiation of heat in metals. White color and black color possess opposite properties.