The Effects of Electricity on Conductors
A conductor has atoms with loosely-bound electrons, allowing electricity to flow through the material. Most metals make good electrical conductors. Copper and silver are the best at normal temperatures. As electricity moves through most conductors, forces appear. The material resists the flow of electricity, limiting its movement. Electric currents produce other forces, such as magnetism, that stress a conductor under extreme conditions.
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Current
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A flow of electrons in a conductor is called a current. Electrons from a power source, such as a battery, "push" against the free electrons in the conductor. Like pushing forward against the last person in a crowded line, the movement ripples through the substance and passes out of the opposite end. Though the speed of any given electron in a material is low, on the order of hours per inch, the force of the push moves at the speed of light.
Resistance
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Limits exist to the amount of current a conductor can carry. As electrons move in a conductor, they bump against each other and the atoms in the substance, causing a type of friction called electrical resistance. All normal conductors have a certain amount of resistance to current flow. Resistance is a real property measured in units called ohms. Some materials, such as copper, have low resistance. Others, such as lead and carbon, have greater resistance.
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Heat
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As current encounters resistance in a conductor, the energy electrons lost through collisions becomes heat. Toasters, incandescent light bulbs and space heaters put this effect to good use. In most conductors, resistance increases as the temperature rises. In others, such as the silicon used to make transistors, resistance decreases with temperature. Excessive current through a conductor produces so much heat that it melts.
Stress
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All electrons carry a negative electric charge, and, since like charges repel, electricity flowing through a conductor accumulates near its surface and away from its center. Very high currents produce mechanical stresses in thin conductors and can cause them to stress and explode. Current generates a magnetic field around a conductor, which creates its own stress forces--especially if other magnetic fields are nearby.
Superconductors
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In many metals, at temperatures approaching minus 450 degrees Fahrenheit, resistance vanishes completely. Electrical current flows without loss of energy, and scientists call the materials superconductors. A magnetic resonance imaging machine uses a powerful superconducting magnet which, once energized with electricity, carries the same current for years without any additional power input.
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References
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