B. Conductors Homework Part II

100 points



16.3 Capacitance

Remember this: 

Potential Energy =DUc = 1/2CV2 = 1/2QV = 1/2Q2/C = Work = Area under a Voltage vs. Charge (Q) graph.  It has units of N/C, J, N*m

62-66, 69-71

71:  Power has units of Watts (N*m/sec).  Energy has units of Joules (N*m).  Therefore,  Power x time = Energy.  Energy can be either kinetic (KE) or potential (U).  We know a formula for U right?  U = 1/2CV2   (where V = voltage)


16.4  Dielectrics

72, 73, 76, 79, 80

73:  Remember that a dielectric increases the capacitance.  Since C = Q/V and V is a constant from the battery, as C increases, so must Q.

76:  K = C/Co

79:  K = C/Co.  Remember that C = Q/V and Q remains constant, but V changes from 12 Volts to 5 Volts)

80:  Uc = 1/2CV2 solve for C knowing the voltage and the Uc.  Then, find K by comparing C to Co.


16.5 Capacitors in Series and Parallel

81-87, 90, 91

85:  Utotal = 1/2CsV2 solve for Cs.  Since you are given the capacitance of one, you can figure out the other with 1/Cs = 1/C1 + 1/C2).

86:  They are all parallel.  This is easy!

90:  Realize that each capacitor holds a charge in ratio since the voltage is the same for each capacitor in parallel. 

91:  C1 and C2 are parallel.  C3 and C4 are parallel.  The total Cp for 1 and 2 is in series with the total Cp for 3 and 4.  So, find the charge (Q) on Cs1234.  Once you find the total charge (SQ) you can find the voltage on each plate and then the charges (Q) on each plate.

Answers to Even Problems:

62:  d

64:  decreases

66:  2.2 x 10-9 F

70:  a)  same     b)  doubles to 5.0 x 10-8J

72:  b

76:  3.0

80:  2.50

82:  a

84:  a)  0.24mF    b)  1.0mF

86:  1.2mF

90:  C1 = 0.60 mC     C2 = 1.2mC     C3 = 1.8 mC