Download presentation

Presentation is loading. Please wait.

Published byTomas Sherlock Modified over 2 years ago

1
ECE201 Lect-21 Ohm's Law (2.1); Kirchhoff's Laws (2.2) Dr. Holbert January 23, 2006

2
ECE201 Lect-22 Resistors A resistor is a circuit element that dissipates electrical energy (usually as heat) Real-world devices that are modeled by resistors: incandescent light bulbs, heating elements (stoves, heaters, etc.), long wires Resistance is measured in Ohms ( )

3
ECE201 Lect-23 Ohm’s Law v(t) = i(t) R- or -V = I R p(t) = i 2 (t) R = v 2 (t)/R[+ (absorbing)] The Rest of the Circuit Rv(t)v(t) i(t)i(t) + –

4
ECE201 Lect-24 Example: a 25W Bulb If the voltage across a 25W bulb is 120V, what is its resistance? R = V 2 /P = (120V) 2 /25W = 576 What is the current flowing through the 25W bulb? I = V/R = 120V/576 = 0.208 A

5
ECE201 Lect-25 Thought Question When I measured the resistance of a 25W bulb, I got a value of about 40 . What’s wrong here? Answer: The resistance of a wire increases as the temperature increases. For tungsten, the temperature coefficient of resistivity is 4.5x10 -3 / o K. A light bulb operates at about 5000 o F.

6
ECE201 Lect-26 Open Circuit What if R= ? i(t) = v(t)/R = 0 The Rest of the Circuit v(t)v(t) i(t)=0 + –

7
ECE201 Lect-27 Short Circuit What if R=0? v(t) = R i(t) = 0 The Rest of the Circuit v(t)=0 i(t)i(t) + –

8
ECE201 Lect-28 Class Example Learning Extension E2.1(a) Learning Extension E2.2(a)

9
ECE201 Lect-29 Kirchhoff’s Laws Kirchhoff’s Current Law (KCL) –sum of all currents entering a node is zero –sum of currents entering node is equal to sum of currents leaving node Kirchhoff’s Voltage Law (KVL) –sum of voltages around any loop in a circuit is zero

10
ECE201 Lect-210 KCL (Kirchhoff’s Current Law) The sum of currents entering the node is zero: Analogy: mass flow at pipe junction i 1 (t) i 2 (t)i 4 (t) i 5 (t) i 3 (t)

11
ECE201 Lect-211 Class Examples Learning Extension E2.3(b) Learning Extension E2.4 Learning Extension E2.5(a)

12
ECE201 Lect-212 KVL (Kirchhoff’s Voltage Law) The sum of voltages around a loop is zero: Analogy: pressure drop thru pipe loop v1(t)v1(t) + + – – v2(t)v2(t) v3(t)v3(t) +–+–

13
ECE201 Lect-213 KVL Polarity A loop is any closed path through a circuit in which no node is encountered more than once Voltage Polarity Convention –A voltage encountered + to - is positive –A voltage encountered - to + is negative

14
ECE201 Lect-214 Class Examples Learning Extension E2.6 –Use two different directions Learning Extension E2.7

15
ECE201 Lect-215 Electrical Analogies (Physical)

Similar presentations

OK

Lecture #2 OUTLINE Circuit element I-V characteristics Construction of a circuit model Kirchhoff’s laws – a closer look.

Lecture #2 OUTLINE Circuit element I-V characteristics Construction of a circuit model Kirchhoff’s laws – a closer look.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Download ppt on coordinate geometry for class 9th 2015 Ppt on nature and human mix Ppt on access modifiers in java Ppt on basics of object oriented programming Download ppt on zener diode Ppt on product specification Numeric display ppt on tv Ppt on video teleconferencing installation Ppt on e-commerce business models Ppt on strategic leadership