1. Ohm’s Law Physics 12

2. Conductors vs. Insulators In 1729 Stephen Gray observed the movement of electric charge on some materials while not on others As a result he classified materials as either: Conductors – objects that allow electric charge to move Conductors – objects that allow electric charge to move Insulator – objects that restrict the movement of electric charge Insulator – objects that restrict the movement of electric charge

3. Moving Beyond Electrostatics As a result of Gray’s discovery, scientists began to move beyond electrostatics and start to consider moving electric charges In 1800, Alessandro Volta added to this new branch of charge theory when he invented the electrochemical cell His cell was the first voltaic pile (or battery) and consisted of layers of silver, zinc and salt water soaked paper

4. Voltaic Cell One of the silver, zinc and salt water soaked discs became known as a voltaic cell A voltaic cell requires: Cathode (positive end) Cathode (positive end) Anode (negative end) Anode (negative end) Electrolyte (to allow the movement of charge) Electrolyte (to allow the movement of charge)

5. Electric Current Electric current describes the flow of charge carriers through a conductor If we were discussing the flow of water, it is likely we would consider a flow rate in litres per second; when it comes to charge, we consider charge per second (one ampere is equal to one coulomb per second)

6. Current vs. Electron Flow By convention, current is assumed to be the flow of positive particles (from cathode to anode) However, we now know that electrons are the charge carriers and have a negative charge (flow from anode to cathode) So the direction of current flow and electron flow are in opposite directions

7. Electric Circuits An electric circuit exists anytime a closed loop exists that involves a battery and some type of load Charge carriers will flow from the battery with high electric potential, give off their electric potential as they cross the load and then return to the battery to regain electric potential

8. Resistance In a way that is similar to friction opposing motion, electrical resistance opposes the flow of charge carriers Resistance is measured in ohms and is a function of the material that is conducting charge carriers This leads to Ohm’s Law

9. Practice Problems Voltage Page 692 Page 6921-3Current Page 696 Page 6964-11 Ohms Law Page 714 Page 71421-26