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8.1 - Electric Potential Energy and Voltage : (page 250) We store electrical charges inside “electrochemical cells”.(what a consumer would call a battery) They change chemical energy into electrical energy. How ? They keep oppositely charged substances separated inside them, creating a difference in energy between two places ( terminals ). (stretched spring or climbing stairs analogy) Why ? These cells are energy sources. Energy is the ability to do work. Potential energy is the energy stored inside an object. Electric potential energy is the energy stored inside these things because of separated charges, and they have the ability to do work when hooked up to a path (“circuit”) and electrons can flow around this path. (electrical kinetic energy)http://www.explainthatstuff.com/how-lithium-ion-batteries-work.html How Stored Energy is Measured : The amount of energy it takes to make one coulomb of stored charge is called the “potential difference” or “voltage” ( after the Italian physicist Alessandro Volta). It is a measure of how much energy the cell can put out. A battery’s potential energy depends on 2 things.... how much voltage the battery has ( the difference in potential energy between 2 parts....how different they are in terms of giving up electrons the amount of separated charge ( how many electrons we have separated) Voltage of a cell is measured using a “voltmeter”. or Different cells might be marked as having the same voltage...but the one that has the largest separated charges and more coulombs of force has more potential energy in it. Types of Cells and How They Work : (253) http://michaelbluejay.com/batteries/ C - Zn : Lithium : http://electronics.howstuffworks.com/lithium-ion-battery1.htm Batteries..... Each has two “terminals” or “electrodes” made of 2 different metals ( sometimes a metal and carbon/graphite )...A negative (anode) terminal (where electrons are concentrated) and a positive (cathode) terminal (where there are fewer electrons). There will also be an “electrolyte”, or substance that conducts electricity between the two electrodes. This is a paste or gel on a “dry cell”, and it is a liquid in a “wet cell”. One electrode reacts with the electrolyte to give up atoms, leaving some E behind (-), the other electrode gives up electrons ( +) and a difference (voltage) is created. Modern Battery Chemistry Modern batteries use a variety of chemicals to power their reactions. Typical battery chemistries include: Zinc-carbon battery - Also known as a standard carbon battery, zinc-carbon chemistry is used in all inexpensive AA, C and D dry-cell batteries. The electrodes are zinc and carbon, with an acidic paste between them that serves as the electrolyte. Alkaline battery - Alkaline chemistry is used in common Duracell and Energizer batteries, the electrodes are zinc and manganese-oxide, with an alkaline electrolyte. Lithium-iodide battery - Lithium-iodide chemistry is used in pacemakers and hearing aides because of their long life. Lead-acid battery - Lead-acid chemistry is used in automobiles, the electrodes are made of lead and lead-oxide with a strong acidic electrolyte (rechargeable). Nickel-cadmium battery - The electrodes are nickel-hydroxide and cadmium, with potassiumhydroxide as the electrolyte (rechargeable). Nickel-metal hydride battery - This battery is rapidly replacing nickel-cadmium because it does not suffer from the memory effect that nickel-cadmiums do (rechargeable). Lithium-ion battery - With a very good power-to-weight ratio, this is often found in high-end laptop computers and cell phones (rechargeable). Zinc-air battery - This battery is lightweight and rechargeable. Zinc-mercury oxide battery - This is often used in hearing-aids. Silver-zinc battery - This is used in aeronautical applications because the power-to-weight ratio is good. Reading Check Questions 1-9, page 255 “Many Sources of Electrical Energy”, page 254 Electric eel and electrogenic cells , page 258 Science uses the term “battery” to refer to a number of these cells connected together. The voltage ( electric potential) of a “battery” is the total of all individual cells added together. Ex. Combining six 1.5 volt “cells” together makes a 9 volt “battery” 8.2 - Electric Current : (page 260) “Current electricity” is the flow of charged particles around a path ( “circuit”). Current is measured in “amperes” (A). One amp = 1 coulomb of electrons passing a point on the path per second. Aperes can be measured using an “ammeter”. Or Circuits : When the two terminals are connected by one shared conductor, electrons can flow through a completed “closed” or unbroken path to make something work or move (the “electrical load”). Loads could be sound devices, light, motors, or heat generating devices. They cause a drop in voltage returning to the cell, since some of the potential energy is transformed into heat, light, sound or movement. All circuits include... An energy source A conducting path A control switch - An electric load - Water slide analogy - page 261 (Cells, batteries, or devices from page 254) ( wire ) (opens or closes the path to control electron movement) (Devices converting current electricity into light, sound, heat, or some other form) Simple circuits can be sketched using a standard set of symbols ( page 262 ) and rules. These “circuit diagrams” are square or rectangular drawings that show what all parts of a circuit are, and how they are connected. Reading check questions - page 262 Drawing circuits, page 263