Which of the following is an example of convection?

• A. Heat transfer by electromagnetic waves.
• B. Warm air rising.
• C. Currents in water caused by boiling.
• D. Heat transfer by direct contact.

Answer: (B)

Convection is heat transfer that happens because a fluid (like air or water) moves. When part of the fluid is heated, it becomes less dense and tends to rise, while cooler, denser fluid moves in to take its place. This creates a circulating flow that carries heat with it.

Warm air rising is a classic example of convection: the heated air near a heater becomes lighter and rises, and as it cools it sinks and the cycle continues. Currents in water caused by boiling are another demonstration of convection, since the hot water at the bottom rises and cooler water moves downward to replace it, setting up a moving loop that transports heat.

For contrast, heat transfer by electromagnetic waves is radiation, which does not require a medium to move the heat. Heat transfer by direct contact is conduction, where energy moves through touching substances or through a stationary fluid without bulk movement.