Question

A cold steel serving spoon is dipped in hot mushroom soup. It transfers heat to its other end by process of:
A. Convection
B. Conduction
C. Radiation
D. None

Answer 1

Hint: Note that for the heat transfer to take place, the spoon has to be kept in direct contact with the hot soup. This means that the heat transfer occurs due to a difference in temperature between the spoon and the soup. Here, the heat transfer is not due to any bulk movement of matter but due to vibrations and collisions intrinsically on the molecular scale.

Complete answer:
We know that when the cold steel spoon is dipped in hot mushroom soup there is some heat transfer between the soup and the spoon. We have to deduce the kind of heat transfer process that facilitates this heating up of the spoon.
We see that the heat transfer happens when the serving spoon comes in contact with the soup. This type of heat transfer that involves thermal energy being transmitted via direct contact is called conduction. It occurs as a result of diffusion of heat between the constituent molecules of the material of the serving spoon.
On a molecular scale, the temperature of the material basically measures how fast the molecules are moving and the heat measures the total amount of energy possessed by the material as a result of vibrations of the molecules. Conduction happens when one part of the material is heated and is transferred from regions of high energy to regions of low energy. The molecules in this part absorb thermal energy and vibrate faster and collide more often with their neighbouring molecules. These collisions cause the other molecules to move faster and collide with more molecules. In this way the thermal energy gets transmitted throughout the solid, much like the way energy passes along a set of toppling dominos.
Thus, the part of the spoon that is in contact with the spoon absorbs thermal energy and the molecules at this end of the spoon begin vibrating and colliding with the neighbouring molecules and this vibrational propagation of heat continues as long as the spoon is in contact with the soup and until the heat is distributed throughout the spoon.
Thus, the transfer of heat between the soup and the spoon is done by conduction.

Note:
Remember that conduction requires physical contact to occur and is a molecular/ atomic process, whereas convection is a bulk process where there is a bulk movement of fluid.
Conduction takes place due to a difference in the temperature between two objects whereas convection takes place due to difference in density.
The movement of clouds, or the working of heaters are all based on convection.
Radiation is the process by which heat transfer occurs through electromagnetic waves, and is the fastest form of heat transfer. This is the process that facilitates heat transfer from the Sun to the Earth, or why we are able to warm up in front of a wire even if the air is cold.