Circuits Chapter 23

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

Basic Symbols Used for Electric Circuit Drawings

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

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

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

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

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

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

Kirchhoff’s Junction Law

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

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.

Kirchhoff’s Laws Slide 23-11

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

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

Clicker Question The diagram below shows a segment of a circuit. What is the current in the 200 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

Answer The diagram below shows a segment of a circuit. What is the current in the 200 resistor? B. 1.0 A Answer: B Slide 23-14

Clicker Question The diagram below shows a circuit with two batteries and three resistors. What is the potential difference across the 200 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

Answer The diagram below shows a circuit with two batteries and three resistors. What is the potential difference across the 200 resistor? 2.0 V Answer: A Slide 23-16

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

Series Resistors Slide 23-17

Parallel Resistors Slide 23-18

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