Q) Why does the filament of a light bulb light up, when an electrical current is passed through it ?
A) To explain this we must remember that an electrical current is a flow of electrons. As the electrons pass through the wire they collide with the atoms of the wire and some of the kinetic energy of the electrons is transfered to the atoms. This makes the atoms move slightly and gain kinetic energy, the atoms "heat up". As the atoms gain more and more energy the filament begins to glow white hot and light is produced. The amount of light produced depends on how much energy is delivered by the electrons. The larger the current the more electrons that are flowing and the more energy is delivered. The amount of energy that is delivered is called the Power and this is the amount of energy that is delivered every second. This process of heating by electrical current is called Ohmic Heating and is important in many aspects of the Solar Corona. It is possible that coronal loops may be heated by Ohmic Heating .