Multiloop Circuits PH 203 Professor Lee Carkner Lecture 13
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 +
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
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
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
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
Next Time No class Friday or Monday No lab tomorrow (Thurs) Class next Tues + Wed Read Problems: Ch 27, P: 19, 20, 26, 46
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
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
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