Elements of the Solar Cell
Solar cells operate by taking the sun’s radiant energy and converting it directly into electric current. The element selenium was the first substance from which these cells were made. The element silicon one of the most abundant element in earth converts a much higher % of suns rays in to electricity .
A solar cell consists of a very thin wafer of silicon over which a delicate meral grid is applied . the grid harvests electrons from silicon without shading it from sun. One cell by itself produces too little power for practical purpose , so many cells are usually connected in a series.
Construction
Although you can buy the cells in electronic stores , a discarded older model portable radio can provide raw materials for the construction of our own cell. The current produced will be very small , but you’ll ger a response from a galvanometer.
Open the radio and remove the selenium rectifier from inside. The rectifier from has a panel of six plates, each with a copper brown selenium wafer soldered at the ends. With a little cleaning and right connections , each plate can function as a cell.
Carefully cur the plates from the rectifier, and remove any paint with lacquer thinner on a soft cloth. Avoid rubbing too vigorously ,you don’t want to scratch the delicate selenium surface.Glue the plates , metal side down to sthe strip of cardboard. Space them evenly.
Cut the red wire unto six 2 inch pieces and the blue wire into six 4 inch pieces. Lay the pieces out in pairs. Cut the thin foil into small squares , just large enough to act as contact pads for the wire tips . Now with a tiny bit of solder connect one end of both red and blue wires to the contact pads , leaving the other ends free.
With small strips of tape, attach the contact pads of the blue wires to the selenium squares. Tape the contact pads of the red wires to the metal bases . Splice the six blue wires to the longer piece of the blue wire for the galvanometer . Splice the six red wires into a larger piece of red wire , functioning as a positive lead wire.
Shine a strong light on the panels . Watch the needle swing as it registers an electric current. With a strong light source and many more cells connected in series , you could even light a 6 volt flash light bulb or power a small motor.
Wind Turbines
Wind turbines are elegant application of the faradays principle.
In a wind farm each wind mill is an electric generator, since movement of a powerful magnet attached to the propeller creates electrical energy in a coil. A small electronic apparatus the diode keeps the current flowing through in a single direction.
Construction
Wrap about 200 turns of wire around one of the 3 inch nails for the coil .Leave 1 inch of space at the nail’s bottom to hammer it into the wood base. Remember to leave a few inches of free wire at the coils beginning and end for connections. Twist the wires ends together once or twice to prevent unraveling.
Hammer the large nail to the centre of the wooden base and hammer two smaller nails behind it so that the three nails form a triangle. Loop the free ends of coil wire once around each smaller nail and connect them with the diode at the base of this triangle of nails.
With glue attach the bar magnet to the head of the other 3 inch nail. Allow the glue to dry. Center the magnet on the nail head so that it spins cleanly when the nail – now a propeller shaft – revolves.
For the supports, measure ¾ inch from the bottoms of the brass strips , and bend each strip 90 degrees at that place . Hold one of the strips, with bend side down, against the wooden base to determine where to drill holes for the propeller shaft.
Make sure the end of the shaft with the attached magnet just clears the coils top.
If your magnet is a little longer than 1 inch , you may need longer strips for supports or need to build up existing supports with thin sheets of masonite .
Carefully drill holes in both supports, making sure the holes line up .Then screw the supports to the wooden base directly in front of the coil, with bent ends facing inward. Poke the shaft through the holes so that the magnet sits directly above the top of the coil. Wrap a little electrical tape around shaft on both sides of each hole so that both shaft and magnet stay in position. Finally attach the propeller to the end of the shaft. There should be a little hole in the back of the propeller. If it slips use tape for a spacer.
To test the turbine , connect the wires of the galvanometer to the small nails. Position an electric fan in front of the propeller and switch it on. Watch the compass needle jump as your turbine creates electricity from the wind.
Making Movies
Before the invention of the motion picture camera, many odd devices brought still pictures to life, creating the illusion of motion.One such device, the zoetrope, meant “wheel of life”. Other devices where mutoscope or flip book, phenkistoscope and kinetoscope.
The principle of these devices are the same. Separate sequential images flash by at high speeds, fooling the brain into seeing one continuous image in motion. Each separate image persists in the brain for 1/16 of a second. Images flashing by at speeds greater than this blend into a single moving picture.
Mutoscope
We’ll construct the simplest device, the mutoscope. Draw a simple design on every page of a small stiff notepad, starting at the back. Make each design relate to the one before it. If you begin with a square and gradually round off the square’s corners and want to turn it into a circle, for instance, gradually round off the corners of the square’s corners in the next few drawings. If you want your square to revolve, tilt the square a little more in each drawing, allowing drawings to naturally flow into one another. This ensures smooth images when you flip.
When you finish your drawings, flip through the pad like a deck of cards, from back to front. Your design comes to life.
Electrostatic Airplane
You can make toys like airplane which operate on the principle of static electricity.
An electrostatic airplane consists of a thin piece of aluminum foil, cut into the shape of a small airplane, and an inflated balloon mounted at the tip of a 12 inch dowel.
Cut the foil airplane pattern and fold the plane along the dotted line. Then unfold it, but do not flatten it completely. Fold the tail flaps up along the dotted line. Attach a few squares of tape to the nose to improve the flight.
Inflate the balloon and stretch the neck over the tip of the dowel. Wrap tape around the end of the dowel to ensure a tight fit, as necessary.
Rub wool or fur against the balloon to give it a negative charge. Toss the airplane in the air and touch it with the balloon. Now both airplane and balloon have negative charges and will repel each other. Use the balloon to keep your airplane in the air by repulsion. If you find that the balloon on a dowel is too unwieldy, try substituting a plastic baseball bat or any other plastic rod or wand. Rub it vigorously with wool or fur as before.
Materials Required
Optical Illusions
Working together , the eye and brain provide information about our environment.
But both eye and brain can be fooled, creating optical illusions. This project demonstrates how eye and brain interpret motion together and what happens when the perception mechanism becomes fatigued.
Spinning Spiral
Measure the phonograph turntables diameter. Tie one end of the string a little more than half that diameter to a pencil. Using cellophane tape, attach the other end of the string to the middle of the poster board Draw a circle by pulling the pencil tight against the string and swinging it around. Before you detach the string from the poster board, mark the center of the circle. Cut out the circle, punch a hole through the center mark and place this paper “record” on the phonograph turntable.
Switch the record player to 45 rpm or medium speed. As the record spins, hold a felt tip marker close to the center and slowly drag it out to the edge. You will create a perfectly drawn spiral. To draw a spiral in the opposite direction , flip the record over.
This time, begin at the edge and slowly move the marker towards the center.
Place the turntable 1.8m away. Tape the cloud picture to the wall ,and clearly illuminate it. If possible, increase the phonograph speed to 78 rpm. Look down at the turntable and stare at the spinning spiral for about 30 seconds. For 45 rpm, stare at the spiral for about 1 minute.
Now quickly look up and stare at the cloud picture , The clouds appear to move. This effect persists for 20 s even if u look away and back again. Notice too that the clouds seem to move in a direction opposite to that of the spin of the spiral. If the spiral moves inward the clouds appear to drift towards you. If you flip the record over and reverse the spiral’s direction , the clouds appear to move away.
What’s happening:
Receptors in the eyes work with the brain to detect inward and outward motion. When you look at stationary objects, inward and outward receptors are in balance. But when you look at a spiraling pattern, the stimulation makes one set of receptors tired. As you stare at the cloud picture, resting receptors take over, and that’s ehy you see motion in the opposite direction.
This works best with objects with vague or complex outlines. That’s why cloud forms demonstrate this effect dramatically. But trees and rock formations work almost as well, and you could try substituting other pictures.