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Transcript
Physics 212 and 222 Current and Resistance TOC Current Batteries Basic Circuit Elements 1 Physics 212 and 222 Current and Resistance •Current is a measure of the movement of charge TOC 2 Physics 212 and 222 Current and Resistance TOC Current is defined as the amount of charge that passes through a surface in a given amount of time. Q I t The units of current are amps Q The direction of the current is opposite to the flow of electrons. It may be thought of as the flow of positive charge. 3 Current always flows from higher potential to lower potential. Physics 212 and 222 Current and Resistance TOC A battery uses chemical reactions to cause a potential difference between the terminals + - The maximum value of the potential difference of a battery is called its voltage In a circuit diagram we draw it like this V + 4 - Physics 212 and 222 Current and Resistance This is how an alkaline cell (AA battery) works. TOC Zn + 2 OH- —> ZnO + H2O + 2 e2 MnO2 + H2O + 2 e- —>Mn2O3 + 2 OH- Cathode (MnO2) Mn2O3 MnO2 MnO2 5 Anode (Zn) ZnO OH HOH O 2 - Zn Zn + 2MnO2 —> ZnO + Mn2O3 + 1.5 V Physics 212 and 222 Current and Resistance Current is defined as the amount of charge that passes through a surface in a given amount of time TOC Q I t The units of current are amps (A) The direction of current is opposite to the flow of electrons The current may be though of as the flow of positive charge Current always flows from higher potential to lower potential In other words, current flows from the positive terminal of the battery through the circuit to the negative terminal V In a circuit diagram we draw it like this 6 + I - Physics 212 and 222 Current and Resistance TOC The following circuit elements and their symbolic representation are the ones most commonly found in circuits. Name Battery Symbol - + V Resistor Capacitor Inductor V R Ω F C H L Switch S 7 Units Physics 212 and 222 Current and Resistance TOC Current Batteries Basic Circuit Elements 8