Question

State the mode or different modes of heat transfer in the following situations.
(a) A paper cup, full of hot soup lying on a table.
(b) Cooking vegetables in a pan.
(c) Melting of a chocolate bar in the school bag on a hot day.
(d) Cooking food in a microwave oven.

Answer 1

Hint: Heat transfer is characterized by thermodynamic systems as the heat flow across a system's boundary caused by the temperature difference between the body's surrounding and itself. Conduction, convection, and radiation are the three mechanisms of heat transfer. We can choose one of the three available modes of transfer for each case.

Complete answer:
We should understand that heat energy can travel from one region to another region in a number of ways. This motion of heat can be classified in three main ways:
-Heat transfer by conduction: Conduction is the movement of heat energy from substances which possess higher temperatures to other substances which possess comparatively lower temperatures.
-Heat transfer by convection: Convection is defined as the migration of the particles of a fluid again from higher to lower temperature areas.
-Heat transfer by radiation: The specific outcome due to spontaneous atoms and molecular motions in substances bring about thermal radiation or radiation due to heat.

The scenarios and their mode of heat transfer will be:
(a) Mode of heat transfer here is convection. This is because hot soup is a type of liquid and generally in fluids or liquids the mode of transfer of heat is convection. The molecules of the liquid will spread the heat over the cup and slowly move to the table and cool down the liquid soup.

(b) Mode of heat transfer here is conduction. This is because for cooking we require vegetables to experience the heat that comes from the pan. We place vegetables in a pan which is placed on some heat source so that cooking of vegetables takes place, so the pan transfers heat onto the vegetable through conduction.

(c) Mode of heat transfer here is conduction. This is because the chocolate when placed in the bag experiences the heat transferred from the bag. On a hot day the bag gets heated up when kept outside so the hot bag conducts heat onto the chocolate placed inside it.

(d) Mode of heat transfer here is radiation. This is because the microwave oven functions by giving off heat. This heat gets transferred onto any food placed in the microwave without having to come into direct contact with the heat source. The heat surrounding the food item placed inside the oven will heat the food so it is radiation.

Note: Keep in mind that almost all of the day to day activities require the transfer of heat and they can take any mode. But the mode of transfer of heat that can happen the quickest compared to others is the mode of radiation. It is due to its principle of movement that includes tiny particles that move continuously along with high speed. The other modes require an external factor such as temperature difference.