Question

Take a round bottom flask. Fill it two-thirds with water. Place it on a tripod so that you can heat it by placing a candle below it. Wait till the water in the flask is still. Place a crystal of potassium permanganate at the bottom of the flask gently using a straw. Now, heat the water by placing the candle just below the crystal. You will observe that when water is heated,the water near the flame gets hot. Hot water rises up.The cold water from thes sides moves down towards the source of heat. This water also gets hot and rises and water from the sides moves down.This process continues till the whole water gets heated. State the mode of heat transfer

Answer 1

You might have observed that a frying pan becomes hot when kept on a flame. It is because the heat passes from the flame to the utensil. When the pan is removed from the fire, it slowly cools down. Why does it cool down? The heat is transferred from the pan to the surroundings. So you can understand that in both cases, the heat flows from a hotter object to a colder object. In fact, in all cases heat flows from a hotter object to a colder object.

Answer 2

The mode of heat transfer is Convection.

• Convection is the mode of heat transfer which generally takes place in liquid and gasses.
• In this case, in the convection mode of heat transfer, the molecules of the liquid which are in close contact with the candle, get more heat energy at a given time compared to the water molecules at the top.
• Then, the molecules with more heat energy transfer the heat energy to the molecules with less heat energy.
• In this process, convection happens here.