Модуль 2 - Времена группы Continuous и Perfect Active Voice (1096806), страница 8
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When current flows through the coiled circuit, another magneticfield is produced. The north pole of the fixed magnet attracts the south pole of the coiled wire. Thetwo north poles push away, or repulse, each other. The motor is set up in a way that attraction andrepulsion spins the center section with the coiled wire.2.Stored Energy and BatteriesEnergy cannot be in a battery. When connected in a circuit, a battery can produce electricity.If you look at a battery, it will have two ends &emdash; a positive terminal and a negative terminal.If you connect the two terminals with wire, a circuit is formed.
Electrons will flow through the wireand a current of electricity is produced.Inside the battery, a reaction between the chemicals takes place. But reaction takes place only if thereis a flow of electrons. Batteries can be stored for a long time and still work because the chemicalprocess doesn't start until the electrons flow from the negative to the positive terminals through acircuit.How the Chemical Reaction Takes Place in a BatteryA very simple modern battery is the zinc-carbon battery, called the carbon battery for short.32This battery contains acidic material within and a rod of zinc down the center.
Here's where knowinga little bit of chemistry helps.When zinc is inserted into an acid, the acid begins to eat away at the zinc, releasing hydrogen gas andheat energy. The acid molecules break up into its components: usually hydrogen and other atoms.The process releases electrons from the Zinc atoms that combine with hydrogen ions in the acid tocreate the hydrogen gas.If a rod of carbon is inserted into the acid, the acid does nothing to it.But if you connect the carbon rod to the zinc rod with a wire, creating a circuit, electrons will beginto flow through the wire and combine with hydrogen on the carbon rod.
This still releases a little bitof hydrogen gas but it makes less heat. Some of that heat energy is the energy that is flowing throughthe circuit.The energy in that circuit can now light a light bulb in a flashlight or turn a small motor. Dependingon the size of the battery, it can even start an automobile.Eventually, the zinc rod is completely dissolved by the acid in the battery, and the battery can nolonger be used.For a "great" on-line page about batteries, visit the Energizer Learning Center.SidebarAs we read in Chapter 1, Alessandro Volta created the first battery (alsosee our "Super Scientists" page).Volta called his battery the Voltaic Pile.
He stacked alternating layers ofzinc, cardboard soaked in salt water and silver. It looked like this:If you attach a wire to the top and bottom of the pile, you create an electriccurrent because of the flow of electrons. Adding another layer will increasethe amount of electricity produced by the pile.Different Types of BatteriesDifferent types of batteries use different types of chemicals and chemicalreactions. Some of the more common types of batteries are:••••••Alkaline battery – Used in Duracell® and Energizer® and otheralkaline batteries. The electrodes are zinc and manganese-oxide.
Theelectrolyte is an alkaline paste.Lead-acid battery – These are used in automobiles. The electrodes are made of lead and leadoxide with a strong acid as the electrolyte.Lithium battery – These batteries are used in cameras for the flash bulb. They are made withlithium, lithium-iodide and lead-iodide. They can supply surges of electricity for the flash.Lithium-ion battery – These batteries are found in laptop computers, cell phones and other highuse portable equipment.Nickel-cadmium or NiCad battery – The electrodes are nickel-hydroxide and cadmium. Theelectrolyte is potassium-hydroxide.Zinc-carbon battery or standard carbon battery – Zinc and carbon are used in all regular orstandard AA, C and D dry-cell batteries.
The electrodes are made of zinc and carbon, with apaste of acidic materials between them serving as the electrolyte.Food – Another Method of Storing Energy33Batteries store energy in a chemical process, but there are other ways of storing energy. Consider the"food chain" on our planet.Plants, like grass in a meadow, convert the sun's energy through photosynthesis into stored chemicalenergy. This energy is stored in the plant cells is used by the plant to grow, repair itself andreproduce itself.Cows and other animals eat the energy stored in the grass or grain and convert that energy into storedenergy in their bodies.
When we eat meat and other animal products, we in turn, store that energy inour own bodies. We use the stored energy to walk, run, ride a bike or even read a page on theInternet.3. Turbines, Generators and Power PlantsAs we learned earlier, electricity flows through wires to light our lamps, run TVs, computers and allother electrical appliances. But where does the electricity come from?In this chapter, we'll learn how electricity is generated in a power plant.
In the next few chapters,we'll learn about the various resources that are used to make the heat to produce electricity. Thenwe'll learn how the electricity gets from the power plant to homes, school and businesses.Pic. 1Pic. 2Thermal power plants have big boilers that burn a fuel to make heat.
A boiler is like a teapot on astove. When the water boils, the steam comes through a tiny hole on the top of the spout. The movingsteam makes a whistle that tells you the water has boiled. In a power plant, the water is brought to aboil inside the boiler, and the steam is then piped to the turbine through very thick pipes.In most boilers, wood, coal, oil or natural gas is burned in a firebox to make heat. Running through thefire box and above that hot fire are a series of pipes with water running through them. The heat energyis conducted into the metal pipes, heating the water in the pipes until it boils into steam.
Water boilsinto steam at 212 degrees Fahrenheit or 100 degrees Celsius.The first picture is of a small power plant located at Michigan State University. The black area to theleft of the power plant is coal, the energy source that is burned to heat the water in the boilers of thisplant.In the second picture, you'll see the turbine and generator at MSU's power plant. The big pipe on theleft side is the steam inlet. On the right side of the turbine is where the steam comes out. The steam isfed under high pressure to the turbine. The turbine spins and its shaft is connected to a turbogeneratorthat changes the mechanical spinning energy into electricity.34Pic.
3The third picture on the left is of the turbine fan before it is placed inside the turbine housing. Youcan see a close-up of the turbine blades on the fourth picture. The turbine has many hundreds ofblades that are turned at an angle like the blades of a fan. When the steam hits the blades they spinthe turbine's shaft that is attached to the bottom of the blades.After the steam goes through the turbine, it usually goes to a cooling tower outside the where thesteam cools off. It cools off and becomes water again. When the hot pipes come into contact withcool air, some water vapor in the air is heated and steam is given off above the cooling towers. That'swhy you see huge white clouds sometimes being given off by the cooling towers. It's not smoke, butis water vapor or steam.
This is not the same steam that is used inside the turbine. The cooled waterthen goes back into the boiler where it is heated again and the process repeats over and over.Most power plants in California use cleaner-burning natural gas to produce electricity. Others use oilor coal to heat the water. Nuclear power plants use nuclear energy to heat water to make electricity.Still others, called geothermal power plants, use steam or hot water found naturally below the earth'ssurface without burning a fuel. We'll learn about those energy sources in the next few chapters.How the Generator WorksThe turbine is attached by a shaft to the turbogenerator. The generatorhas a long, coiled wire on its shaft surrounded by a giant magnet. Youcan see the inside of the generator coil with all its wires in the pictureon the right.The shaft that comes out of the turbine is connected to the generator.When the turbine turns, the shaft and rotor is turned.
As the shaftinside the generator turns, an electric current is produced in the wire.The electric generator is converting mechanical, moving energy intoelectrical energy.The generator is based on the principle of "electromagnetic induction"discovered in 1831 by Michael Faraday, a British scientist. Faradaydiscovered that if an electric conductor, like a copper wire, is moved35through a magnetic field, electric current will flow (or "be induced") in the conductor. So themechanical energy of the moving wire is converted into the electric energy of the current that flowsin the wire.The electricity produced by the generator then flows through huge transmission wires that link thepower plants to our homes, school and businesses.All power plants have turbines and generators.
Some turbines are turned by wind, some by water,some by steam.363738.
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