1. Multiloop Circuits PH 203 Professor Lee Carkner Lecture 13

2. Potential  Every circuit element has a potential associated with it   For a battery: V =    The potential can be positive or negative   Through the battery from negative to positive is + 

3. Batteries and Direction   Two batteries connected in opposite directions will subtract their voltages   In some cases you can’t tell by inspection which add and which subtract  Use Kirchhoff’s rules

4. Grounding  Sometimes we will connect part of the circuit to the earth or some other object that can absorb a nearly infinite amount of charge  Called grounding   Can use to define zero point of potential system

5. Potential Between Points   The potential difference V B – V A is the sum of the potential differences of all of the elements along the path, A to B   V B -V A is V f -V i   e.g., forward through battery is positive, backwards through battery is negative, etc.  Can use to find the potential at one point in circuit, if you know the potential at some other point

6. Energy and Batteries   Resistors have P = i 2 R = V 2 /R that is removed from the circuit   The sum of all power removed by resistors must be equal to all power added by batteries 

7. Next Time  No class Friday or Monday  No lab tomorrow (Thurs)  Class next Tues + Wed  Read 27.8-27.9  Problems: Ch 27, P: 19, 20, 26, 46

8. Three light bulbs with resistance R 1 = 1 , R 2 = 2  and R 3 = 3  are connected in series to a battery. Which has the largest potential drop across it? A)R 1 B)R 2 C)R 3 D)All have the same potential drop E)It depends on the voltage of the battery

9. Three light bulbs with resistance R 1 = 1 , R 2 = 2  and R 3 = 3  are connected in parallel to a battery. Which has the largest current through it? A)R 1 B)R 2 C)R 3 D)All have the same current E)It depends on the voltage of the battery

10. A string of Christmas trees lights are connected in series. If one light is removed and replaced with a normal wire, A)The other lights get dimmer B)The other lights get brighter C)The other lights don’t change D)It depends on the current in the wire E)It depends on the voltage across the wire