1. Cells and Batteries

2. Electrons are involved in static charge – we know! How does this relate to electronic devices? Electric circuits! ▫ A closed path along which electrons that are powered by an energy source, can flow

3. Cells and Batteries Most batteries used today are similar to Alessandro Volta’s “Voltaic pile” Voltaic cells generate an electric current by chemical reactions between 2 different metals separated by a conducting solution Battery = a connection of 2 or more cells Clarification: a regular AA battery is technically a cell

4. Batteries A battery is essentially a can full of chemicals that produce electrons 2 terminals (electrodes): +ve and –ve ▫ Made of different metals ▫ Immersed in electrolyte (solution or paste) If you connect a wire between electrodes, electrons will flow (from -ve end to +ve) as fast as they can ▫ Wears out the battery quickly ▫ Dangerous ▫ Use a load

5. Batteries Inside battery, a chemical reaction produces ions ▫ Takes place at surface of electrode Electrons travel through connecting wire to positive electrode ▫ Attracted to +ve electrode The -ve metal disintegrates slowly ▫ Limits the life of a cell

6. Types of Cells DryWet Electrolyte is a paste Uses zinc and carbon Major advance came with alkaline cells  More expensive  Last longer Electrolyte is a liquid Most use sulfuric acid

7. Types of Cells Dry Wet

8. Types of Cells Primary – can be used only once Secondary – can be recharged many times ▫ Electric current is passed in opposite direction through cell  Reverses the chemical reactions, restoring cell to full capacity Fuel cell – generates electricity through chemical reactions of fuel that is stored outside the cell ▫ Eg. Hydrogen stored in a tank combined with Oxygen

9. For Homework: Read pg 511-513 Answer questions p. 513 #4, 5, 7