Electricity/Magnetism

Electricity is one of our most important forms of energy. It illuminates are nights, powers our factories and heats many of our homes. Like so many other very familiar and ubiquitous things around us, we sometimes fail to appreciate their origin and their relationship to other natural things. Electricity, like other forms of energy, obeys the basic physical principle that it cannot be created or destroyed only changed from one energy form to another. So what is it and how do we produce it?

First of all, electricity is the energy resulting from the movement of charged particles. These particles are the building blocks of the atoms of all things--rocks, air and are own bodies. Two of the three particles that constitute atoms, electrons and protons, have a property in addition to their mass called charge. It happens that the charge on these two particles is different, so scientists, for want of a better term, arbitrarily have called the charge on the electron negative and the one on the proton, positive. As you may remember from high school science, like charges (two negative or two positive) repel each other and unlike charges (a positive and a negative) attract each other.

Luckily, the total number of positive and negative charges in atoms are normally equal. Therefore, the effects cancel each other and things are electrically neutral, i.e. appear to have no charge.

If by some means electrons are dislodged from their atoms (relatively easy in metals that is why they are good conductors of electricity) and get them moving, an electric current results. Of course, it takes countless billions of electrons moving together to accomplish any real work. A battery, by chemical action, strips some electrons from atoms and delivers them to one terminal while atoms now with a net positive charge remain at the other terminal. If an external conducting path is provided, a current will flow. Electrons will move toward the positive terminal attempting to restore the electrical balance. An electric current continues to flow until the battery chemicals are depleted. Since the current produced by a battery always flows in one direction (negative to positive), it is called direct current (DC).

The lights in our homes and businesses are not powered from batteries, but rather from the alternating current (AC) power line. The electrons in our house wiring go no where but accomplish their work by simply oscillating back and forth 60 times a second. Alternating current is created by power plant generators using the principle of electromagnetism.

Around every magnet is a field of force. That’s what every science student has seen traced out by iron filings on a surface above a magnet. If a conductor (a wire or coil of wire) is moved across a magnetic field or a magnetic field is moved in relation to the conductor, an electric current will flow in the conductor. The electrons in the conductor ‘feel’ the magnetic force and are accelerated by it. The current only flows while either the conductor or magnetic field is moving and stops when either motion ceases.

An electric generator is a device that rotates a huge coil of wire through a powerful magnetic field to create an electric current. The coil is rotated by a turbine powered from falling water, the wind, or steam generated from water by burning coal, oil, or by the heat of a nuclear reactor. As the coil rotates, the conductor moves up through the magnetic field and then down through it with each rotation. The result is that the current changes direction with each rotation resulting in alternating current.

The word electromagnetism suggests the intimate relationship between electricity and magnetism. They are like the two sides of the same coin. While a magnetic field can create an electric current, an electric current also creates a magnetic field around the conductor. A magnetic field is frequently concentrated by winding the conductor into a coil around a iron core. This forms an electromagnet which is energized whenever current is applied to the coil. Such a device in a form called a solenoid, is used to convert an electric current into a mechanical action. Solenoids operate such things as water valves in wash machines, dishwashers, etc. Solenoids in devices called relays can also remotely operate switches that can turn things on and off like your furnace .