1. Capacitors Physics 102: Lecture 04

2. Recall from last lecture….. Electric Fields, Electric Potential

17. A parallel plate capacitor given a charge q. The plates are then pulled a small distance further apart. What happens to the charge q on each plate of the capacitor? ACT: Parallel Plates 1) Increases 2) Constant 3) Decreases Remember charge is real/physical. There is no place for the charges to go. +q -q + + + + - - - - d pull pull

18. A parallel plate capacitor given a charge q. The plates are then pulled a small distance further apart. Which of the following apply to the situation after the plates have been moved? 1)The capacitance increases True False 2)The electric field increases True False 3)The voltage between the plates increases True False Preflight 4.1 +q -q + + + + - - - - d pull pull

19. A parallel plate capacitor given a charge q. The plates are then pulled a small distance further apart. Which of the following apply to the situation after the plates have been moved? ACT/Preflight 4.1 The energy stored in the capacitor A) increases B) constant C) decreases +q -q + + + + - - - - d pull pull

21. Two identical parallel plate capacitors are shown in end-view in A) of the figure. Each has a capacitance of C. A ) B ) If the two are joined as in (B) of the figure, forming a single capacitor, what is the final capacitance? 1) 2C 2) C 3) C/2 ACT/Preflight 4.2

33. A circuit consists of three initially uncharged capacitors C 1 , C 2 , and C 3 , which are then connected to a battery of emf  . The capacitors obtain charges q 1 , q 2 ,q 3 , and have voltages across their plates V 1 , V 2 , and V 3 . 1) q 1 = q 2 Not necessarily C 1 and C 2 are NOT in series. 2) q 2 = q 3 Yes! C 2 and C 3 are in series. ACT/Preflight 4.4: Which is true? C 2 C 3 C 1 E + - -q 2 +q 1 -q 1 +q 3 -q 3 +q 2 V 1 V 2 V 3

34. 1) V 2 = V 3 Not necessarily, only if C 1 = C 2 2) E = V 1 Yes! Both ends are connected by wires A circuit consists of three initially uncharged capacitors C 1 , C 2 , and C 3 , which are then connected to a battery of emf  . The capacitors obtain charges q 1 , q 2 ,q 3 , and have voltages across their plates V 1 , V 2 , and V 3 . ACT/Preflight 4.4: Which is true? C 2 C 3 C 1 E + - -q 2 +q 1 -q 1 +q 3 -q 3 +q 2 V 1 V 2 V 3 10V 0V 7V??

35. 1) V 1 < V 2 Nope, V 1 > V 2 . (E.g. V 1 = 10-0, V 2 =10-7) 2) C eq > C 1 Yes! C 1 is in parallel with C 23 A circuit consists of three initially uncharged capacitors C 1 , C 2 , and C 3 , which are then connected to a battery of emf  . The capacitors obtain charges q 1 , q 2 ,q 3 , and have voltages across their plates V 1 , V 2 , and V 3 . ACT/Preflight 4.4: Which is true? C 2 C 3 C 1 E + - -q 2 +q 1 -q 1 +q 3 -q 3 +q 2 V 1 V 2 V 3 10V 0V 7V??