Ivan and Cassie, of Balclutha Primary School, asks :-

Why does light make heat?

Daniel Schumayer, a physicist at the University of Otago, responded.

Heat is a form of energy. There are many different forms of energy, e.g. if a body moves, it has energy due to its motion. If it moves faster, it has more energy.

Now, let us imagine that you go to the beach and walk into the ocean until it reaches your neck. You are standing and waiting for the waves. Since you are standing still, your energy is zero. As the waves are coming in to the shore, these waves will sway you back and forth. If they are strong enough and reach you regularly they may even make you lose your balance. Your motional state has changed as you started moving, therefore, you have gained energy from the wave and the wave has lost energy.

Light is also a wave and in some respects quite similar to the ocean wave. If it reaches an object, the light waves hit the atoms in the material, just like ocean waves hit you, and make the atoms move faster, thus giving them energy. At the same time the lightwaves lose energy. Since the atoms are now wiggling faster, they have more energy than beforehand. We may also say that the temperature of the object increases, because temperature measures how rapidly the atoms move inside the objects. The swifter the atoms, the higher the temperature. Interestingly, this process can and does happen in the opposite direction. Just think about a heating coil on a stove. If it is really hot it glows with a reddish colour.

There is an important fact we have to notice though. Light does not make heat out of nothing, but simply transfers a portion of its own energy to the material it collides with.

I hope this mystery about light is now enlightened and I hope that you keep asking such interesting questions. Nature is interesting!