Electricity for the 4-H Scientist.
by Eric B. Wilson.
LESSON NO. B-l
Credit Points 3
GETTING ACQUAINTED WITH ELECTRICITY
Electricity serves you best when you understand how it works and use it properly. As a 4-H member, you should know about electricity and help to show others the way to obtain its tremendous work-saving benefits as well as how to use it with safety.
A good way to think of electricity is to compare it with water. It acts a lot like water. However it is made of tiny parts of atoms called electrons. When there are more than the normal number of electrons in anything, it is said to be negatively charged; when there is a shortage of electrons, it is positively charged. As water flows downhill, "seeking it"s level," electrons flow from negative to positive, seeking to "balance" the charge.
Electrical Conductors
Even if you"re never going to repair a lamp or make a chick brooder, you should know about conductors and insulators. This is because you happen to be a fairly good conductor of electricity. Electricity will pa.s.s easily through you to other conductors--the ground, for instance. When this happens you may get a shock, burn, or serious injury. But it doesn"t ever have to happen, if you learn to understand your friend, electricity.
Silver, copper, iron, aluminum and many other metals are very good conductors. Water, acids, and salts are too. Electricity pa.s.ses over or through them very easily. Like water pipes, the larger the conductor, the more electricity it can carry. When conductors are too small for the amount of electrons trying to move over them, they get hot, melt, may start fires. That"s why wire size is important.
Electrical Insulators
Insulators are the opposite of conductors. Electricity has trouble pa.s.sing through some materials. Rubber, most plastics, dry wood, oils and gla.s.s are some of the good insulators. It"s the amount and kind of insulation that counts. If it has enough force, electricity can pa.s.s through just about anything--even jump gaps!
Electricity, like water, flows along the easiest paths. It is always trying to get to the ground. The earth attracts it. It stays on the wires unless a person, a wet branch, or some other conductor gives it a path to the ground. Do not touch any wire which might be carrying electricity.
Play It Safe
If you should touch a "hot" wire accidentally and are standing on a dry piece of wood, the conducting pathway to the ground is not good and the electricity may keep running along its wire. But do not touch some other conductor with another part of your body. This would complete a circuit through your body and would be very dangerous. Always make sure there is plenty of good insulation material or plenty of distance between you and anything which might be carrying electricity.
Remember, too, insulation is of little use when it is wet. Dew, mist, rain, condensation, a damp floor can change the whole picture. If you understand electricity and how it acts, you"ll be safe enough, because you won"t take chances or expose yourself to injury.
Electrical Terms
_Alternating Current_--Usually referred to as "AC," alternating current is current which reverses its direction of flow at regular intervals, 60 times a second.
_Direct Current_--"DC" current flows only in one direction. Battery current is DC.
_Ampere_--Amperes are units by which the rate of flow of electrical current (electrons) is measured. An ampere is 6.3 billion electrons pa.s.sing one point in a circuit, in one second. This compares with the way the flow of water is measured in gallons per second.
_Volts_--A volt is a unit to measure the tendency of electrons to move when they are shoved. Voltage is the amount of "push" behind the electrons. It"s like water pressure in a pipe. Home power lines carry 115 volts (110 to 120 volts). For appliances such as electric stoves, washers and driers, a second 115-volt line should be added, giving 230 volts (220 to 240 volts).
_Watts_--Watts equal volts times amperes. Light bulbs, electric irons and other appliances are usually marked with the voltage they require and the number of watts.
_Kilowatts_--Your electric bill usually reads in kilowatt hours. A kilowatt is 1000 watts. A kilowatt hour equals 1000 watts used for 1 hour. One kilowatt equals about 1-1/3 horsepower. A kilowatt is usually indicated by "kw" and a kilowatt hour by "kwh."
_Circuits_--A closed circuit is one in which the electricity is flowing, lighting a light, running a motor, or some other appliance. The circuit runs all the way from the place the electricity is being generated to your home, through the appliance or light bulb, and back to the generator.
Circuits are opened and closed by switches. When the circuit is opened, the electricity stops at the switch. Before working on a switch, socket, fuse, or any part of the wiring be sure to open the main switch. The main switch is usually at the fuse box or near it. Appliances should be disconnected when you work on them. Everyone in the family should know where the main switch is so it can be pulled in case of accidents, fire, flood, or windstorm damage.
_Fuses and Circuit Breakers_--These are the safety valves of your electrical system. The different electrical circuits in your home are meant to carry only certain amounts of electricity. Some carry only 15 amps, others can carry 20 or more. They are marked to show capacity.
When a fuse burns out or a circuit breaker opens, look for an overload of lights and appliances on the circuit before you try to replace the fuse or close the circuit breaker. Without these safeguards, the overloaded electric line will heat up and may start a fire. Even if no fire starts, electricity will be wasted and the homeowner will be paying for electricity that"s doing no good.
Remember: If you ever have to replace a fuse, pull the main switch first. Keep a flashlight handy in your house. It seems that fuses usually blow at night, and it doesn"t pay to stumble or fumble around electric wires in the dark.
WHAT TO DO: Make A Circuit Board
So that you can show others how electricity travels from here to there, and how it behaves under different conditions, make an electric circuit board.
_Materials Needed:_
Piece of 3/4" board about 4" x 6"
l-l/2-volt No. 6 dry cell battery Two pieces of bell wire, each 24" long, one black, one white Two 10-penny box nails (3") Three 3-penny box nails (1") Two small screws or carpet tacks Two 2-inch rubber bands Two miniature sockets with solder terminals Two l-l/2-volt flashlight bulbs
_Tools Needed:_ Ruler, pencils, hammer, pliers or vise.
_Making the Board:_
1. Lay out the board with a pencil and ruler as indicated in Figure 1.
2. Bend the three-inch nail as shown in Figure 2, using pliers, vise and hammer.
3. Pound the one-inch nails into the board for a half-inch at points A, C, and D. Use the three-inch nail to make a hole a half-inch deep at B.
Put the crank nail in this hole and pound in a little farther. Attach the lamp socket brackets at E and F. Stretch the rubber band as in Figure 3.
4. Lay out the electricity path, the circuit (Figure 3). Use the black wire for the positive side of the circuit (the center pole of battery).
Twist it around the switch crank B, and the center pole of battery. Run another piece to the outside terminal of bulb socket at E. Run white piece to negative pole of battery from the other terminal at E.
[Ill.u.s.tration: Figure 1 (Circuit Board)]
[Ill.u.s.tration: Figure 2 (Switch)]
5. Close the switch. The rubber band should hold the switch nail tightly against nail at C. Does the bulb light? __________ If it doesn"t, check the connections.
Now you have a circuit--a closed circuit when the electricity runs all the way from the positive pole to the negative pole. The black wire is the hot side, the live wire, because it carries the full load of the battery up to the bulb.
Remember, battery current is direct current, DC. In the case of alternating current, AC, such as most homes and buildings use, the electricity flows in first one direction and then the other.