Brent Anderson, age 17, of Phoenix, Arizona, for his question:
How can waterfalls be used to make electricity?
Every day we see electric power at work warming our ovens cooking our food and lighting our glowing lamps. Like fire, it gives us heat and light and the great enemy of fire, of course, is water. It seems odd that water, the fire douser, can be used to provide electricity, the giver of heat and light.
Water is a substance with many useful features and without the Earth's abundant supplies of it life as we know it would be impossible. It is needed to dilute, liquefy and dissolve the chemicals in living plant and animal cells and, of course, it is used to put out fires. Neither of these qualities of water, however, is needed to make electric power. This job depends upon the weight of falling water, and the weight of almost any other tumbling liquid might be used just as well.
It so happens that water is very plentiful and nature has arranged for lots of it to tumble over cascading cataracts and waterfalls. This falling water has weight and strength enough to move objects in its way. A pushing power of this kind is needed to turn the turbines that generate electricity, and a free falling waterfall is just the giant for the job.
Electricity is generated when copper is turned around and around so that it cuts the invisible lines of force surrounding a magnet. A looped circuit of copper wire to and from the generator carries the current to be tapped and used over a wide area. In some generators, a mighty magnet is whirled around and around masses of copper coils, in others the copper is twirled around the magnet. In both cases, the copper cuts through the lines of magnetic force and in both cases a constant pushing power is needed to keep the big wheels turning.
In olden days, a water wheel was used to turn the stones for grinding the millets wheat. The wheel was rimmed with tipping buckets placed to catch the waters of a tumbling stream. This extra weight started the wheel rolling and as other buckets got their turn under the water. The first buckets tipped and emptied around and around, again and again. In much the same way, a waterfall turns the great wheels linked to the twirling parts of an electric generator. And the force of falling water is used to generate electric power.
We do not know why electricity is generated when copper cuts through a magnetic field. But we know how to put this secret of nature to good use. The current must have a circuit, a loop of wires running from and back again to the generator. This is why a length of electric wiring is made from two strands of sheathed copper. Each strand is one side of a long, long loop stretching way back to where its two ends are connected to a generator.