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Transcript
MODULE 3: Basic Circuits - Resistance SUMMER CHALLENGE Electrical Engineering: Smart Lighting Michael Rahaim, PhD Candidate Multimedia Communications Lab Boston University [email protected] Module 3: Basic Circuits 07/08/2015 Overview Boston Circuits Review University Slideshow Title Goes Here Resistance and Resistors Ohms Law Breadboards Capacitance Experiments Resistive Circuit Voltage Divider RC Circuit 2 Module 3: Basic Circuits 07/08/2015 Recap - What is a Circuit? Boston InUniversity a circuit, how are the start and end related? Slideshow Title Goes Here They’re the same! What happens if there isn’t a continuous path? Open Circuit – No flow of charge (or electrons) What happens when a conduit connects two points? Charge (and electrons) can flow between the points Short Circuit – Directly connecting two points of different voltage Switch Device that can open or close a circuit 3 Module 3: Basic Circuits 07/08/2015 Resistance Boston AsUniversity charge flows from high to low V, energy is released Slideshow Title Goes Here Where does it go?? As electrons flow, they encounter resistance Friction from electrons moving against the resistance generates heat Resistance is a function of material, length, and cross-sectional area Resistance is measured in Ohms [Ω] Wires have resistance, but it is minimal and a direct connection between different voltage levels is a short The filament in an incandescent light introduces resistance The heat energy causes the filament to “glow” white-hot and produce light Incandescent Light 4 Module 3: Basic Circuits 07/08/2015 Resistors Boston University Slideshow Title Goes Here ?? ?? ?? 5 Module 3: Basic Circuits 07/08/2015 ?? Law Ohms German professor who published a book in 1827 Boston University Slideshow Title Goes Here that includes what is now known as Ohm's law 𝑉 = 𝐼𝑅 Ohm's Law: Voltage across a resistor is directly proportional to the current flowing through it. + 𝑉 = 𝐼𝑅 - i𝐼 v R - + The proportionality constant is the resistance! 𝑉 𝐼= 𝑅 Georg Simon Ohm (1789 – 1854) 𝑉 𝑅= 𝐼 What happens in the case of an open circuit (i.e., 𝑅 ≈ ∞)? What happens in the case of a short circuit (i.e., 𝑅 ≈ 0)? 6 Module 3: Basic Circuits 07/08/2015 Series vs Parallel V0 V1 V2 IR1 IR2 I R1 R2 Boston Series Resistance University Slideshow Title Goes Here I IRs + + A Rs V Rs R1 R2 V2 R2 V0 I V1 R1 - Parallel Resistance I I I V V V 1 1 V 1 2 R1 R2 R R I Rp 2 1 I I1 V R1 I2 R2 V Rp 1 1 1 Rp R1 R2 Rp R1 R2 R1 R2 7 Module 3: Basic Circuits 07/08/2015 Breadboards Why do we use breadboards? Boston University Slideshow Title Goes Here Temporary Circuits Prototyping No Soldering 8 Module 3: Basic Circuits 07/08/2015 Anatomy of a Breadboard Boston University Slideshow Title Goes Here 9 Module 3: Basic Circuits 07/08/2015 Boston University Slideshow Title Goes Here POSITIVE NEGATIVE RESISTOR LED 10 Module 3: Basic Circuits 07/08/2015 SHORT EXERCISE 1. Copy the schematic. 2. Label where each of the numbers are. Boston University Slideshow Title Goes Here 1 8 7 6 2 3 4 5 11 Module 3: Basic Circuits 07/08/2015 Voltage Divider Circuit I Boston University Slideshow Title Goes Here R1 V1 R2 V2 V0 V0 I Rs R1 R2 A V0 R1 Also V1 V0 R1 R2 V0 V2 IR2 R2 R1 R2 R2 V2 V0 R1 R2 12 Module 3: Basic Circuits 07/08/2015 Experiment I Boston Voltage Divider University Slideshow Title Goes Here Resistive Circuits 13 Module 3: Basic Circuits 07/08/2015 Capacitance Boston A University capacitor has capacity to store energy in the form of Slideshow Title Goes Here electrical charge producing a voltage across plates Storage of energy leads to time dependency This was NOT the case in purely resistive circuits. Capacitance is measured in Farads [𝐹] 𝑖 = Instantaneous Current d𝑣 𝑖=𝐶 d𝑣 = Instantaneous rate of d𝑡 d𝑡 voltage change Capacitors are sometimes polarized 𝜀𝐴 𝐶= 𝑑 𝜀 = Permittivity of dielectric 𝐴 = Area of plate overlap 𝑑 = distance between plates NOTE: Directly connecting a capacitor to a voltage supply isn’t practical 14 Module 3: Basic Circuits 07/08/2015 RC Circuits Boston RC circuits consist of a resistor and capacitor in series University Slideshow Title Goes Here How do capacitors react to a sudden change in voltage? 𝜏 ≡ 𝑅𝐶 𝑉𝑐 = 𝑉𝑠 1 − 𝑒 −𝑡 𝜏 15 Module 3: Basic Circuits 07/08/2015 RC Circuits Boston Charge University Slideshow Title Goes Here Discharge 16 Module 3: Basic Circuits 07/08/2015 Experiment II Boston Resistor – Capacitor (RC) Circuits University Slideshow Title Goes Here 17 Module 3: Basic Circuits 07/08/2015 Recap Boston What did you University Slideshow Title Goes Here today? 18