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Electricity and Magnetism It’s An Electric World There are many natural and manufactured objects that use electricity. Natural occurring electricity would be electricity such as lightning, electric eels, electric rays, electric catfish, static electricity, brain and nerve impulses. This electricity happens by itself in nature. The electricity used by humans which is manufactured would include electricity such as toasters, light bulbs, fans, cars, electric construction tools, clocks, school buzzers, and electromagnets for moving scrap metal. This is most commonly known as current electricity. Natural Electricity Static electricity is created whenever a material with loosely bonded electrons (hair, fur, nylon, silk) rubs against a non-conducting material that strongly attracts electrons (plastic, rubber) in a relatively dry environment. Moisture in the air (humidity) discharges static electricity as it is created. Lightning is caused by electrical discharge released from a thundercloud that has become electrically imbalanced. As thunderclouds churn, positive charges (protons) accumulate near the top of the cloud while negative charges (electrons) concentrate near the bottom. The separation of charges makes the cloud electrically imbalanced within itself, as well as in relation to the other clouds around it, or the ground. Lightning results when the electrical imbalance equalizes itself (negative charges jump to adjacent positively charged objects). The flash we see is caused by molecules of air that are heated by friction to the point of glowing. Heated air along the path of lightning expands and contracts quickly, creating sound waves (thunder). Plants use an electrical force (about 0.1 V) to obtain nutrients from the soil and draw them up into their root cells. Some plants use electricity to respond to touch (mimosa plant leaves close up when touched). The coiling of tendrils of climbing plants is also thought to be an electrical response. Electric eels and other electric fish have organs along the sides of their bodies that build up a charge that can be used for sensing their environment, protecting themselves against predators, and obtaining food. Electric eels can produce a charge up to 600 volts, which is enough to light up ten, 40 watt light bulbs. This voltage is strong enough to stun organisms as large as a horse or a human, causing them to stop breathing and therefore drown. Sharks and rays communicate using electric signals, which other fish can pick up in the water. The human body runs on electricity that is generated when different electrically charged particles move between cells and surrounding fluids in the body. Everything you do depends on tiny electrical impulses of about 0.1 V traveling through your body. Your brain operates on approximately 10 watts of electricity, the same amount required to light up a string of outdoor Christmas lights. Injuries heal faster because an electrical current begins to flow from a cut or wound which trigger cell division and makes nerves in the injured area grow faster. Your brain, nervous system, and muscles work because of electricity. Your nerves act like a telephone line transmitting tiny electrical impulses to and from your brain, however, the amount of electricity used to send these messages is not enough to light a tiny LED (light-emitting diode that generally uses less than 2V). Current Electricity A larger electrical current, such as the 120 V household current, will override your body's low voltage causing a disruption of message transmission. Thus a shock from an electrical appliance may cause the muscles and brain to stop functioning and cause death. Please remember not to attempt any investigation, at home or at school, using the electrical current provided by the wall outlets (plug ins) or any electrical devices that use the household power supply. There are dangers associated with current electricity and care should be taken to avoid short circuits. Short circuits may cause wires to heat up and can start fires. Safety Rules Electrons are always looking for the shortest, easiest pathway to the ground. Electricity will leave the wires or electrical device if it can find an easier path to follow. Our bodies are 70% water ( a good conductor of electricity) and so humans can become the shortest pathway to the ground if we come in contact with an electrical current and the ground ( or something touching the ground such as a tree or ladder) at the same time. Hot Stuff The electricity produced by a D-cell battery is totally safe and is not strong enough to harm anyone. You will feel heat generated when two terminals of the battery are connected. Without a load, (such as a light bulb), to provide resistance, electrons flow and create friction with the material in the wire, and so cause the wire to heat up. If you keep the wire connected to the battery without a load, you will drain the battery of its energy. In A Flash-Burning Steel Wool The electricity flowing through the battery and steel wool had no resistance (load) to pass through. The friction of the moving electrons was sufficient to heat up the steel wool and cause it to burn. Lights On! Will It Light? A bulb will light whenever the electric current produced by the battery can flow from the battery through the bulb and back to the battery. The flow of the electrons is from the negative (-) terminal to the circuit and back to the positive (+) Bulbs Electrons flow in through the metal at the side-bottom of the bulb. Then the electrons flow up the wires in the support towers and through the filament (thin, curly wire), which glows. Electric energy is changed into light energy. Electricity flows out through the metal bump at the very bottom of the bulb. The air inside the glass bulb has been taken out at the factory and replaced with a gas (argon). This prevents the filament from burning out too quickly. The electric current can enter the bulb through either of the lead contacts. Electricity is conducted across the threaded base, to the lead contact, up the support, across the filament, down the other support, and out through the other lead contact back into the circuit. The direction of electrons’ flow can be opposite to the above, depending on which way the bulb is connected to the battery. The insulating ceramic disc separates the threaded base and lead contact on the bottom of the base preventing a short circuit. More Wires There is a method of shorthand that is used for electrical drawings. This method is useful in that it minimizes the time required to draw, and it is universal because it is understood by everyone who knows the symbols. Light Sockets and Battery Holders There are many ways to open and close circuits. Electrons prefer to travel through “the path of least resistance” rather than travel through the bulb. Please take care not to touch the wires together as a short circuit will be created and the bulb will go out. Open and Closed Circuits When we hear the word circuit, it brings to mind certain other words, such as “circle”, cycle, etc. It means that something is in an unbroken line. An open circuit is one which does NOT allow a complete path for the electricity to flow through. A closed circuit is one that does allow a complete path and causes the bulb to light. If the wires in your home were to touch each other, then the current traveling through the wires is able to produce enough heat to produce a fire. This is why it is very important not to use an appliance with a torn or frayed cord. Bare copper wire (that is, not coated with a plastic or rubber coating) might have a clear insulation sprayed onto it, and as a result will not conduct electricity. If you want to conduct electricity then you may want to sand the edges of the wire to remove the coating. Short Circuits Always be very careful when working with wires and batteries. The bare ends of the wires can become extremely hot if they touch. Shorted circuits will quickly drain a battery. There is heat generated in a short circuit, by the friction between electrons in the wire. A short circuit is when there is a "short cut" for electrons to avoid passing through the load (e.g. light bulb) After all experiments dealing with electricity, please disconnect wires from dry cells. Usually electricity will follow the easiest, shortest path back to its source. This is known as the "path of least resistance." If electricity is allowed to flow for more than a few minutes, the wires will begin to heat up. The "easier" path created (no load) allows too much current to flow, heating up the wires. You can apply this concept to the 120 V current used in homes and businesses, not to mention the appliance cords when they are frayed or cracked. THE HEAT GENERATED COULD CAUSE A FIRE!!!! Fuses prevent circuits from overheating and causing fires. A fuse prevents a fire by melting and breaking the circuit before the wires get too hot. Making a Switch A complete circuit is comprised of a power source, a switch to control the power flow, connectors through which the current can flow, and a load (e.g. light bulb, motor, heater, etc.) Two-way switches can turn a light on or off, either upstairs, or downstairs. This particular circuit requires two double-pole switches which will look like this: Add a Battery When the positive terminal of one battery is connected to the negative terminal of another battery, this is known as a series connection. Batteries connected in a series will cause the bulb to glow brighter and the current must flow through both batteries to the load and back. Any opening of a connection will cause the bulb to go out. In the series connection, the bulb will burn brighter, but will not last as long as in a parallel connection. If the positive terminal of a battery is connected to the positive terminal of another battery, and the negative terminal of the batteries are also connected to each other, this is a parallel connection. Batteries connected in parallel will not affect the brightness of the bulb and when one battery is taken out of its holder the bulb will continue to glow. In the parallel connection the bulb should burn for twice as long as a circuit containing just one battery. In the old days, Christmas lights were wired in series and if one light bulb went out, the lights on the entire string would go out. Lights are now wired in parallel which means that the current has more than one path to follow, so it one bulb goes out, the rest of the string will continue to burn. The same principle holds for batteries in series and parallel connections. In a series there is only one path for the current to follow. In parallel, the current has more than one path to follow. Illustrations: Series Wiring: Parallel Wiring: A Magnetic Experience Please be careful not to burn your skin during this activity because the wire will heat up as electricity flows through it. If no battery holder is available, then the wire ends should be taped firmly to the end of the battery rather than holding them in place with bare fingers. Usually, an electromagnet is a coil of wire with an iron bar tucked inside. When an electric current flows through a wire, a magnetic field is produced around the wire. A magnetic field is associated with moving electrons so a flow of electrons, as in a current, will have a magnetic field associated with it. The greater the flow of electrons, the stronger the magnetic field that surrounds the wire. Therefore, adding cells in series, makes the electromagnet stronger. Increasing the number of coils of wire also concentrates the magnetic field, as does the iron rod around which the wire is coiled. Using the other non-magnetic metals or other substances does not affect the strength of the magnetic field. Reversing the direction of the coils on the nail cancels out the magnetic field. Electromagnets are used to pull switches off and on, particularly when we do not want to get near extremely powerful currents. Electromagnets turn automatic devices such as refrigerators, street lights, and electric hot water heaters on and off at the appropriate times. Illustration: The Coil and the Magnet Galvanometers are used to detect and measure electric currents. The needle can be placed on a dial that indicates the strength of the current. Converting magnetism into electricity is called magnetic induction. Michael Faraday first discovered this in the early 1800’s. All generators that produce electricity in vehicles and power plants work on this principle. A Field to Remember To check for magnetic fields, iron filings or a compass can be used. If you are using a compass, place the compass needle at various spots around the bar magnet, and record the direction of the compass needle. The same can be done around a single wire carrying a current or around an electromagnet. If a single wire is used, it could be passed through a piece of cardboard before it is connected to the battery. The compass then can be placed at spots around the vertical wire and the needle direction is written down. Magnetic force extends out from a magnetized object to one carrying a current forming what is called a magnetic field. This invisible force field can be made visible indirectly by the use of particles, such as iron filings. The rule is that the greater the number of magnetic field lines, the greater the strength of the magnetic field. On a bar magnet, the number of lines is generally most concentrated at the poles where the strength of the magnet is greatest. In a coil of wire making up an electromagnet, the magnetic field lines are most concentrated through the coil, and pass out at each end. Illustrations: Bar Magnet: Electromagnet Making an Ammeter An ammeter is device used to detect and measure the flow of electricity. There is electricity when there is evidence of magnetic fields around magnets and around current-carrying wires, by use of iron filings or by use of one or more compasses. All Conductors Don’t Drive Trains Materials that will complete a circuit are called conductors and materials that make it difficult for electricity to travel through are known as insulators. Certain atoms will hold onto their electrons very tightly (rubber and plastic). Other atoms allow their electrons to move freely from one atom to the next (most metals). Materials that hold their electrons tightly do not permit electricity to flow and are called insulators. Conductors are just the opposite with freely moving electrons allowing electricity to flow easily. Item such as nails, paper clips, scissors, keys, tacks, pins, dimes, nickels, foil, etc., conduct electricity. Metals are conductors of electricity. Materials such as plastic, glass, chalk, wood, styrofoam (nonmetals) do not conduct electricity. Most non-metals are non-conductors of electricity. Some common insulators are: rubber, glass, plastic. Rubber is used to make gloves for electricians. Plastic coatings insulate many wires. Good conductors include: copper, silver, and salt water. Most wiring is made of copper. Non-conductors, or insulators, help us to use electricity safely. Some examples of this are: insulation around a power cord, insulated handle on an electric teakettle. You must be very careful when using electricity around a conductor (e.g. using a radio in the bathroom). Some materials act as insulators in certain situations, but can conduct electricity when more batteries are used. For example, under low voltage circumstances, tungsten will act as an insulator and will not allow electrons to move through it. With higher voltage, more energy is available to push the electrons through the tungsten and it acts as a conductor. All materials will conduct an electric current to some extent at certain voltages or temperatures. An example of this is air, which is normally a good insulator. Air may conduct electric charges when the voltage is high enough (e.g. lightning). A vacuum seal is the only perfect insulator. Insulation in appliances and cords prevents shocks and short circuits. Liquid Conductors or Insulators If you add salt to water, and attach batteries to wires that are then dipped into the water, you will notice bubbles forming around the wires. The bubbles indicate, that even if there is not enough electric current to light a light bulb, there is enough current to cause a chemical reaction around the electrodes (wires). The electricity is splitting water molecules into oxygen and hydrogen. Using electricity around water, or handling devices with wet hands, is dangerous. Also, the human body is 70% water (and salt), so if you touch electricity, it will flow through you. You could be badly hurt. Liquids that contain a noticeable acid, base, or salt are good conductors of electricity. Liquids with only trace amounts of acids, bases, or salts are poor conductors, but may conduct electricity if the voltage is high enough. Resistance Wires Bare copper wire (not coated with plastic coating) may have a clear insulation sprayed on it and as a result it will not conduct electricity. Sanding the ends of the wire with sandpaper will remove the clear insulation. Nichrome wire does not conduct electricity like copper wire. The nichrome is a resistor. A resistor is something that slows down the flow of electrons and so makes them lose energy (heat and light). Some devices in homes that use resistance wire are: dimmers, switches, toasters, stoves, irons, and bulbs. The current passes through a great length of resistance wire, and so causes the electrons to “fade out” ” losing their heat or energy. Turn It Up! The nichrome wire does not allow electrons to pass through it as freely as the copper wire does. The greater the length of nichrome wire the current is forced to ass through, the greater the "resistance"; fewer insufficient electrons pass through to light the bulb. A Pencil Resistor Graphite, as used in the centre of a pencil, does not conduct electricity as well as metal in wire. Electrons will flow into the graphite, but will have a difficult time moving through it; thereby losing some of its energy. There is less voltage left to light the bulb, which makes it glow dim. The longer the graphite path, the lower the voltage. Eventually, the voltage will be too low to light the bulb at all. Applications of this concept are found in volume controls and dimmer switches. Testing the System There are many variables that affect the way an electrical device behaves when connected in a circuit. Some of these are: a) the number of batteries b) voltage of the batteries c) number of bulbs d) type of bulb e) the material from which wires are made f) length of wires g) thickness/thinness of wires Measuring Electricity Usage Learning how to read a household electrical meter helps you to understand your electricity bill. The unit of measure used is the kilowatt-hour (kW). Different devices have different wattages because the wattage is related to the job the device does. To produce enough heat to cook food, a stove must convert a lot of electrical energy into heat energy (notice that all heating and cooling devices have a large wattage). Therefore, it requires a large power supply (it has a high wattage). A clock on the other hand, only needs enough electrical energy to allow its tiny motor to move the hands of the clock. A device draws power based on the amount of energy it needs to work. An interesting fact: The Grand Coulee Hydroelectric Power Plant, located on the Columbia River in the United States, produces 6 million ( 6 000 000) kilowatts of electric power each second. Calculation of Electricity Consumed To calculate the amount of electricity consumed by an appliance, multiply the amount of electricity it demands by the length of time it operates. e.g. If the light bulb in your bedroom demands 100 watts and it is on for 10 hours, it consumes: 100 watts x 10 hours = 1000 watt-hours of electricity=1 kilowatthour (kWh) If you were measuring the distance between Edmonton and Calgary, you would not use millimetres. The larger kilometre unit is more appropriate. Since the watt is a very small unit of measure, it is necessary to convert it to the much larger unit of the kilowatt. A kilowatt is 1000 watts. To convert the wattage of your devices into kilowatts, you divide the number of watts the device uses by 1000. That is you move the decimal three spaces to the left. The total amount of energy used over a period of time by all the electrical devices in your home can be measured by using a household energy meter. To read a household meter, it is important to understand how the dials rotate. The pointer on the first dial rotates clockwise; the second pointer rotates counterclockwise, the third turns clockwise, and so on. As the right dial turns a full revolution, it pushes the next dial causing it to turn. The dial on the right must rotate 10 times before the dial on the left rotates once. This is true of each dial in the sequence. To take a meter reading, copy the numbers indicated by the pointers from right to left because the dial readings change from right to left. You want to stay head of any number changes. If the pointer is between two numbers, copy the lower number. If the number is between 0 and 9, record the 9. Be sure to record all zeros to hold their place value. How Efficient Are You? There is a need to conserve energy to save non-renewable resources and money, and decrease pollution. It is also very important to see that you, by yourself, can make a difference through your own behaviour and through your influence on the behaviour of others. Make a list of things you can do to help save energy: 1. 2. 3. 4. Turn off electrical devices when they are not in use. Use natural sunlight as a source of energy. Shop and compare when purchasing electrical equipment. Use fluorescent lighting instead of incandescent lights, as they can save up to 75 % of lighting costs. It’s Up to You!