6.1 Current Events in History p Galvani’s and Volta’s Experiments lead to cells and batteries. Luigi Galvani (1737 – 1798) discovered that two different metals made a frog’s muscle twitch. Galvani thought it was the frog’s muscle themselves was the source of electricity. Alessandro Volta (1745 – 1827) discovered that it was the two different metals that caused the frog muscles to twitch. He later on made the first practical “battery” by alternating stacking zinc and silver discs one on top of one another interspaced with moist salt saturated paper pads. This eventually lead to the first voltaic cell. This cell could produce a continuous flow of electric charges called a current. The ability to generate a current flow has lead to many of the worlds greatest discoveries and inventions!

6.1 Current Events in History Electromotive Force p. 221 The energy of a cell comes from the chemical reaction within the cell. The chemical reaction supplies the necessary energy to separate the charges allowing the charges to do work outside the cell. The work done on the charges gives the charges potential energy. The difference between the terminals of a cell is the amount of work done per coulomb of charged moved. Emf = 1.5 J/C = 1.5 V for a normal cell For a fully charged cell not supplying current the potential difference is called the electromotive force (emf) of the cell Different types of cells would have different types of emf’s.

6.1 Current Events in History Electric Current p. 22 When Electric charges flow we say a current exists. Electric current equals the amount of charge flowing past a point per unit time. I = Q t Units: 1 Ampere = 1 Coulomb/s (1 A= 1 C/s) Or 1 A = 6.24 x electrons/s Conventional current is the direction that positive charges flow in a circuit. Electron flow is the direction that electrons flow. Note: Electrons would flow in the opposite direction as conventional current!

6.1 Current Events in History Drift Velocity p It might seem that electrons move very quickly in a conducting wire, but that is not the case. In a conducting wire it is the “free electrons” that are being forced to move due to the electromotive force. The speed at which these free electrons travel is called their “drift speed”. To calculate the drift speed of a conductor we need to know the current in the wire, what the wire is made of, the length of wire that the electrons travel through, and the volume of the wire. The actual drift speed of electrons in a wire is around mm/s!

6.1 Current Events in History Representing Electric Circuits: p. 224 Circuits can be drawn by using common symbols These two images show the same circuit. List of common symbols that are used in creating circuit diagrams. Please note that you will find many more symbols for more complex circuits

6.1 Current Events in History How to read the scale on an Ammeter p. 226 Ammeters have more that one scale. Be sure to connect the ammeter correctly to your circuit so that you use the smallest scale without overloading your meter. Once the correct scale has been chosen you simply read that scale on your meter. For example on this meter connected as shown ( 0 – 100 mA scale) the current reading would be: 63.5 mA = A

6.1 Current Events in History Key Questions In this section, you should understand how to solve the following key questions. Page 225 – Quick Check #1 - 3 Page 226– Quick Check #2 Page 229– Review 6.1 #1,4,7, & 8