Summary

• Ohm's Law
• Electric power
• Series and parallel circuits

• Quiz bonus Ch. 20
  
  
  
• Circuit applet



• Kirchhoff's rules
1. Junction rule: conservation of current
2. Loop rule: ΔV_loop = 0

Example #1



• Kirchhoff's rules video




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End of material on Exam I

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• Exam I
• Bring a calculator (no mobile devices allowed) and your prepared 8-½×11 reference sheet
• 3 free-response questions, some with multiple parts (50 pts)
• 7 true/false questions (14 pts)
• 9 multiple-choice questions (36 pts). Three of these require a calculation.



• Lecture learning outcomes
  A student who masters the topics in this lecture will be able to:
• explain Kirchhoff's junction rule in terms of conservation of charge
• explain Kirchhoff's loop rule in terms of conservation of energy
• use Kirchhoff's rules to characterize an electric circuit with multiple loops




• Practice:
  Try these additional examples
Example #2

Example #3



• Prepare:
  Read textbook sections 21-6 and 21-7 before the next lecture

gc6 17.q8
If V = 0 at a point in space, must E = 0 there? ____
If E = 0 at a point in space, must V = 0 there? ____
A. yes . . . yes
B. yes . . . no
C. no . . . yes
D. no . . . no
Answer















sj6 28.18
If the ammeter reads 2.00 A, what is the unknown battery voltage ℰ in Fig. P28.18?
A. 15.2 V
B. 12.6 V
C. 6.50 V
D. 3.33 V

applet

Answer















Walker5e EYU 21.5
Which of the following is the correct statement of Kirchhoff's loop rule for loop 1?



Answer















Walker5e 21.56c
If point A in the figure is grounded (V = 0), what is the electric potential at point D?
A. 0 V
B. −13.42 V
C. +1.58 V
D. +5.53 V
Answer























 



D. no . . . no
There is no general relationship between the value of V and the value of E. Instead, the magnitude of E is equal to the rate at which V decreases over a short distance. Consider the point midway between two positive charges. E is 0 there, but V is high. Or, consider the point midway between two negative charges (not shown below). E is also 0 there, but V is low, because it is negative. Finally, consider the point midway between positive and negative charges of equal magnitude. There E is not 0, because it points toward the negative charge, but V is zero.





















 



B. 12.6 V





















 


Starting in the lower left corner of loop 1 and going clockwise (as indicated by the purple arrow), we go uphill through the battery, downhill with I₃ through the 200-Ω resistor, and downhill with I₁ through the 300-Ω resistor.




















 

C. +1.58 V