1/30/20 Class Concepts • Understanding circuit topology • Identifying nodes, branches & loops in circuits Circuit Topology & • Open & Short circuits Kirchhoff’s Laws • Implied resistance for the branch • V across & I through for the branch • Kirchhoff à Conservation laws EGR 220, Chapter 2 • Current law, KCL (conservation of charge) Jan 30, 2020 • Voltage law, KVL (conservation of energy) 2 Recap: Electricity Concepts Recap: Electricity Concepts • Define in words and with an equation/expression • Define in words and with an equation/expression • Current • Current • Symbol and unit: • Symbol and unit: • • • Resistance • Resistance • Symbol and unit: • Symbol and unit: • • • Voltage • Symbol and unit: • • Power • Symbol and unit: • How is power related to energy? 4 5 1
1/30/20 New Concepts: Defining a Circuit Open & Short Circuits • What elements can be in a circuit? • Energy source – independent and dependent Tasks: • Energy dissipating element • Draw an example of each type of branch • Energy storage elements • Relate each to Ohm’s Law (V = IR) • A “load” • What are V and I in each example? • Give examples of each element Ø (0? <0? >0? ∞ ?) 6 7 * Open & Short Circuits * Open & Short • If there is no current, can there be a voltage drop? Circuits • Examples? Find • If there is no voltage drop, can there be current? • Examples? V & I for resistors • Power Sources • What is the difference between a current source and a R 1 & R 2 voltage source? 8 9 2
1/30/20 New Concepts & Laws Discuss: Nodes & Branches • A branch represents a single element such as a • Node, Branch & Loop voltage source or a resistor. • Series resistors • A node is the point of connection between two or • Series elements; series branches more branches. • Shared: nodes? current? voltage? • Parallel resistors • Parallel elements; parallel branches • Shared: nodes? current? voltage? • KVL: Kirchhoff’s voltage law • KCL: Kirchhoff’s current law 10 11 Identify nodes, branches & loops Identify nodes, branches & loops; series and || elements • How many of each and where are they? • Which elements are in parallel and which are in series? 12 13 3
1/30/20 Nodes, Branches, Loops, Series and Nodes, Branches, Loops, Series & Parallel Parallel 14 15 Kirchhoff’s Current Law, KCL • Current flowing in = current flowing out. Kirchhoff’s Current and • Principle of conservation of ____________? Voltage Laws: • The math expression is: KVL & KCL 16 17 4
1/30/20 Kirchhoff’s Current Law Kirchhoff’s Current Law • Find i 1 , i 2 and i 3 • Label nodes • Write KCL eqn’s • Solve • We will use Ohm’s law when there are resistors in the circuit diagram 18 19 Kirchhoff’s Voltage Law, KVL Kirchhoff’s Voltage Law, KVL For EVERY loop: ΣV loop = 0 Ø Draw and label an electrical circuit that is consistent with the graph shown below. 5
1/30/20 Kirchhoff’s Voltage Law, KVL • The conservation of _________ • Combine Ohm’s law with KVL to solve for ________? R 1 + R 2 v 2 – Kirchhoff’s Voltage Law New Terminology • Apply KVL • Node • Label voltages • Write KVL eqn’s • Branch • We will solve later with mesh analysis • Loop • Series • Parallel 24 25 6
1/30/20 Office & Tutor Hours New Analysis Tools • Office Hours • Ohm’s law • Monday: 10:15 – 11:45 • KVL: Kirchhoff’s voltage law • Tuesday: 1:30 – 2:30 • KCL: Kirchhoff’s current law • Master Tutor • Current divider • Sunday – Thursday evenings there will always be 3 or so master tutors in the Playground • Voltage divider • https://www.smith.edu/qlc/tutoring.html?colEGR=open#PanelEGR • Equivalent resistance • Tani Somolu point person for EGR 220 26 27 Summary • New Concepts • Kirchhoff’s current and voltage laws • Series and parallel combinations Questions? • Open and short circuits • Nodes, branches and loops • Labs • Pre-lab due before lab • One per team for ‘design your own lab’ days • Lab memo completed with partner, one memo per team 7
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