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Current Electricity Electric Potential Difference • Electric potential is the amount of energy per amount of charge • A large amount of potential energy at a place where large amounts of charge are present results in a large electric potential • A small amount of energy for a given amount of charge results in a small electric potential • The difference between two such points (one high potential and the other low) is called electric potential difference Batteries • In 15 seconds, list the many devices you have used this morning that required a battery. How many could you come up with? Light It Up Materials: 1 bulb, 2 alligator clips, 1 battery Task 1: Using the materials provided, find at least 3 ways the bulb can be lit Task 2: Diagram the 3 ways you were able to get the bulb to light Task 3: Diagram at least 3 ways in which you are not able to get the bulb to light Analysis: What causes the bulb to light? What is a Battery? • A mobile source of power called a voltaic cell • Italian physicist Alessandro Volta created the first battery by stacking alternating layers of zinc, brine-soaked cloth, and silver. • This arrangement was called a voltaic pile • The first device to have a lasting current • The first commercial battery was sold in the US in 1898 by the Eveready Battery Company (Energizer) • • • • • Anatomy of a battery Every battery has 2 terminals, positive and negative A cathode connects to the positive terminal An anode connects to the negative terminal Generally known as electrodes, the terminals are where chemical reactions occur The medium that allows the electric charge to flow between the cathode and anode is known as the electrolyte. Electron Flow • We call the flow of electrons electric current • The chemical reactions in the battery create free electrons and positive ions • It is the flow of electrons that cause a lamp to light • Electrons actually flow from the negative terminal to the positive terminal • Electrons flowing in this direction is known as electron flow Conventional Current • Originally the thought was that positive charges could move • Conventional current assumes that positive charges move from the positive terminal to the negative terminal • We now know this is not true, but the convention indicating the direction charges flow remains • http://www.youtube.com/watch?v=Y7Uqe6DyoRU • http://science.discovery.com/videos/deconstructed-how-carbatteries-work.html Circuits • The electrons flow when a path is present between the terminals • We call this closed loop an electric circuit • Electric energy is converted to other forms of energy including kinetic energy, light energy, or heat energy Diagramming Circuits • A schematic is a drawing of an electric circuit Standard symbols include Conducting Wire Fixed Resistor Switch Battery Voltmeter (measures potential difference) Ammeter (measures current) Electric connection Lamp (light) Example