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Energy and power

Another way for energy to be transformed is for it to move from one place to another without being converted to another form. This can occur with heat via conduction, radiation and convection.

Conduction

Superconductor
Metals lose electrical resistance at very low temperatures. This results in strange behaviour. In this image, a magnet is being levitated by its own induced electrical field in the very cold metal beneath it.

You are familiar with conduction. It is what we feel when we pick up something hot. We know that when we heat one end of a metal bar, after a little while, the other end will also warm up. Another term for heat is thermal energy. It is caused by the vibration of atoms or molecules. The more they vibrate the more thermal energy they have. If a material has no thermal energy at all, it would be at zero Kelvin (-273 °C). At this temperature, material takes on very strange properties. For example, metal loses all resistance to electrical flow, and becomes what is known as a ‘super conductor’.

Every material has its own unique conduction properties. A thermal insulator, such as the material inside the walls of a thermos flask, has very low thermal conduction, and metals very high.

Radiation

The Sun generates heat from a thermonuclear process in which hydrogen is converted to helium. This heat is essential for life on Earth and is carried across the 400 million km of mostly empty space that separates us from the Sun by solar radiation. Solar radiation is absorbed by the atmosphere, the sea, the ground, and by plants, and is energy that results in all the weather we have, as well as the life cycle.

Solar radiation
Solar radiation carries the radiative energy of the Sun to Earth across space.

When the ground is heated by the sun, we can feel the heat. What we are feeling is infrared radiation. This is radiation that has a different frequency to visible light, so we cannot see it. Radio waves, visible light, microwaves and gamma rays from atomic explosions are all examples of electromagnetic radiation.

Convection

Heat can be transferred by movement of the material it is in. Because hot water is less dense than cold, it will move to the top. You can see this when you heat water in a pan. This causes the cold water to be pushed down to the bottom, where it is heated in turn, and rises, to push colder water down. When only one part of a body of water is heated, there will be a circulation of water, which distributes the heat around all the water. This is called convection.

Convection
Without convection currents, heat would not transfer in the Earth's mantel and oceans.

Content © Andrew Bone. All rights reserved. Created : September 23, 2013 Last updated :February 14, 2016

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