Convection

When you boil water in a pan, the heated water molecules near the bottom of the pan expand and become less dense. The colder and more dense molecules at the top start to sink, forcing the hotter and less dense ones to rise. When air is heated, it expands and becomes lighter. The colder and heavier air goes down and pushes the hotter and lighter air upward. This happens continuously while the water boils, resulting in a form of heat transfer called convection.

Radiation

When the sun shines, solar energy travels to Earth in the form of waves. The rays of light give heat to the surroundings. As the energy travels in space through waves, heat is transferred from the source to the receiver in a form of heat transfer called radiation.

Try bringing your hand near a lighted candle or bulb without touching it. You will find out that, although it is inches away from the flame, your hand will feel the heat from the candle or bulb. This is because the heat from the lighted source has radiated to your hand. This is the same form of heat transfer that takes place when the sun’s rays radiate to plants to provide them with the sunlight they need for photosynthesis. The sun is millions of kilometers away but its intense heat radiates to Earth and is utilized by the different living things on the planet.