1 / 23

Ohm's Law (2.1) Kirchhoff's Laws (2.2)

Ohm's Law (2.1) Kirchhoff's Laws (2.2). Prof. Phillips January 24, 2003. Resistors. A resistor is a circuit element that dissipates electrical energy (usually as heat)

tashya-stevenson
Download Presentation

Ohm's Law (2.1) Kirchhoff's Laws (2.2)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ohm's Law (2.1)Kirchhoff's Laws (2.2) Prof. Phillips January 24, 2003 lecture2

  2. 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 (W) lecture2

  3. i(t) + The Rest of the Circuit R v(t) – Ohm’s Law • v(t) = i(t) R - or - V = I R • p(t) = i(t)v(t) = i2(t) R = v2(t)/R • Always dissipating or absorbing power (p>0) lecture2

  4. Example: a 25W Bulb • If the voltage across a 25W bulb is 120V, what is its resistance? R = V2/P = (120V)2/25W = 576  • What is the current flowing through the 25W bulb? I = V/R = 120V/576  = 0.208 A = 208 mA lecture2

  5. Thought Question • When I measured the resistance of a 25W bulb, I got a value of about 40W. 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/oK. A light bulb operates at about 5000oF. lecture2

  6. i(t)=0 + The Rest of the Circuit v(t) – Open Circuit • What if R=? • i(t) = v(t)/R = 0 lecture2

  7. i(t) + The Rest of the Circuit v(t)=0 – Short Circuit • What if R=0? • v(t) = i(t) R = 0 lecture2

  8. Class Example lecture2

  9. 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 voltage (drops) around any loop in a circuit is zero lecture2

  10. KCL (Kirchhoff’s Current Law) i1(t) i5(t) The sum of currents entering the node is zero: Analogy: mass flow at pipe junction i2(t) i4(t) i3(t) lecture2

  11. Class Examples lecture2

  12. KVL (Kirchhoff’s Voltage Law) + – • The sum of voltages around a loop is zero: • Analogy: pressure drop thru pipe loop + v2(t) + – v1(t) v3(t) – lecture2

  13. 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 lecture2

  14. Class Examples lecture2

  15. Electrical Analogies (Physical) lecture2

  16. EE Subdisciplines • Communication/Signal Processing • Controls • Electronic Circuits • Electromagnetics • Power • Solid State lecture2

  17. Power • Generation of electrical energy • Storage of electrical energy • Distribution of electrical energy • Rotating machinery-generators, motors lecture2

  18. Electromagnetics • Propagation of electromagnetic energy • Antennas • Very high frequency signals • Fiber optics lecture2

  19. Communications/Signal Proc. • Transmission of information electrically and optically • Modification of signals • enhancement • compression • noise reduction • filtering lecture2

  20. Controls • Changing system inputs to obtain desired outputs • Feedback • Stability lecture2

  21. Solid State • Devices • Transistors • Diodes (LEDs, Laser diodes) • Photodetectors • Miniaturization of electrical devices • Integration of many devices on a single chip lecture2

  22. Digital • Digital (ones and zeros) signals and hardware • Computer architectures • Embedded computer systems • Microprocessors • Microcontrollers • DSP chips lecture2

  23. Personal Systems Scaling lecture2

More Related