Question

Which is the fastest mode of heat transmission?

Answer 1

Hint: As per thermodynamics, heat transmission is the flow of thermal energy from a higher temperature to a lower temperature in the system. The temperature of two spots in the system is like a potential difference, and heat energy flows through this potential difference like vector flux. If we learn about all the modes, then we can find the required answer to this problem.

Complete solution:
In a given system, heat flows via these three following modes-
1) Conduction
2) Convection
3) Radiation
The process in which heat flows through solids, especially in metals, from a higher temperature spot to a lower temperature spot is known as Conduction. In Conduction, heat must flow through the media.
The process in which fluid particles move from a higher temperature spot to a lower temperature spot is known as Convection. In Convection, heat must flow through a media (Gas or Liquid). Boiling of water is a good example where we can observe Convection.
Radiation is the mode of heat transfer where no media is required to enable heat energy flow. Heat energy can propagate through any media or vacuum at the speed of light. Radiation can take place in any state of matter.

Hence, radiation is the fastest mode among these modes of heat transmission.

Note: Conduction is usually slower in gases than in liquids and solids. Convection is not possible in most of the solids. In the radiation process, heat energy propagates with electromagnetic waves. That is why heat energy travels at the speed of light, i.e., $3 \times {10^8}$ meters/second. Radiation is the process that helps heat energy exerted from the Sun to come to the Earth.