Convection

When water is kept in a very hot pan, the entire water heats up due to the process of convection. Convection is the mode of heat transfer that occurs through the movement or circulation of fluids (liquids or gases). In this case, the fluid is the water in the pan.

Explanation:

1. Conduction:
Conduction is the transfer of heat through direct contact between particles of a substance. When the pan is heated, the molecules at the bottom of the pan gain kinetic energy and start vibrating rapidly. These vibrating molecules transfer their energy to the adjacent molecules, causing a chain reaction throughout the pan. However, conduction alone cannot explain why the entire water heats up.

2. Radiation:
Radiation is the transfer of heat through electromagnetic waves. In this case, the hot pan radiates heat in the form of infrared radiation. However, radiation alone cannot explain why the entire water heats up.

3. Convection:
Convection is the primary mode of heat transfer responsible for heating up the entire water in the pan. When the pan is heated, the bottom layer of water in contact with the pan gets heated through conduction. As the water molecules gain kinetic energy, they become less dense and start rising. This creates a flow or circulation of water, known as a convection current. The hot water rises to the top, while the cooler water from the top moves down to replace it. This continuous circulation allows the heat to be distributed throughout the water, resulting in the entire water heating up.

Conclusion:

In conclusion, when water is kept in a very hot pan, the entire water heats up primarily due to convection. Conduction and radiation also play a role in the transfer of heat, but convection is the main mechanism responsible for the uniform heating of the water.