1. Circuits
Chapter 23

2. Circuit Elements and Design
Circuit Diagram – a logical picture of what is connected to what in a circuit
Replace pictures of the circuit elements with symbols

3. Basic Symbols Used for Electric Circuit Drawings

4. Circuit Diagrams
The longer line at one end of the battery symbol represents the positive terminal
The emf is shown beside the battery
Capacitance and resistance are shown beside the symbols
Wires are shown as straight line connections between circuit elements
Higher potentials are put toward the top of the diagram

5. Reading Quiz Which terminal of the battery has a higher potential?
the top terminal
the bottom terminal
Answer: A
Slide 23-4

6. Answer Which terminal of the battery has a higher potential?
the top terminal
Answer: A
Slide 23-5

7. Checking Understanding
The following circuit has a battery, two capacitors and a resistor.
Which of the following circuit diagrams is the best representation of the above circuit?
Answer: A
Slide 23-9

8. Answer
The following circuit has a battery, two capacitors and a resistor.
Which of the following circuit diagrams is the best representation of the above circuit?
Answer: A
Slide 23-10

9. Kirchhoff’s Laws Analyzing a circuit Find:
The potential difference across each circuit component
The current through each circuit component

10. Kirchhoff’s Junction Law

11. Kichhoff’s Loop Law
To apply the loop we must identify which potential differences are negative and which are positive.
Kirchhoff’s Loop law can only be true if at least one of the potential differences ΔVi is negative

12. Kichhoff’s Loop Law
The net change in the electric potential around any loop or closed path must be zero
If we add all the potential differences around the loop formed by the circuit, the sum of these potential difference must be zero.

13. Kirchhoff’s Laws
Slide 23-11

15. ΔVbat can be – or +
ΔVR is always – because potential across a resistor always decreases along the direction of the current
Voltage “drop” across the resistor
Ohm’s law only considered magnitude of current

16. ΣVi = 0 = ΔVbat + ΔVR
ΔVbat = +ε
ΔVR = -IR
ε – IR = 0
I = ε/R

17. Clicker Question
The diagram below shows a segment of a circuit. What is the current in the resistor?
0.5 A
1.0 A
1.5 A
2.0 A
There is not enough information to decide.
Answer: B
Slide 23-13

18. Answer
The diagram below shows a segment of a circuit. What is the current in the resistor?
B. 1.0 A
Answer: B
Slide 23-14

19. Clicker Question
The diagram below shows a circuit with two batteries and three resistors. What is the potential difference across the resistor?
2.0 V
3.0 V
4.5 V
7.5 V
There is not enough information to decide.
Answer: A
Slide 23-15

20. Answer
The diagram below shows a circuit with two batteries and three resistors. What is the potential difference across the resistor?
2.0 V
Answer: A
Slide 23-16

21. Series and Parallel Resistors
Two bulbs are connected in series if they are connected directly to each other with no junctions in between.
If two bulbs are connected at both ends in a circuit they are in parallel
We use equivalent resistance (the resistance of a single resistor which would replace more than one series or parallel resistors in a circuit) to solve circuit problems

22. Series Resistors
Slide 23-17

23. Parallel Resistors
Slide 23-18

24. What is the current out of the battery?
There is a current of 1.0 A in the circuit below. What is the resistance of the unknown circuit element?
What is the current out of the battery?
Slide 23-19