1 / 21

EE 221 Review 1

EE 221 Review 1. Basic components Electric circuits Voltage and current laws. Basics - SI base units. Basics - SI prefixes. Basics - Charge. Two types of charge positive: (proton) negative: (electron, -1.6 10 -19 C) Continuously transferring charge

lee-hewitt
Download Presentation

EE 221 Review 1

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. EE 221 Review 1 Basic components Electric circuits Voltage and current laws

  2. Basics - SI base units

  3. Basics - SI prefixes

  4. Basics - Charge • Two types of charge • positive: (proton) • negative: (electron, -1.6 10-19C) • Continuously transferring charge • total amount of charge never changed • neither created nor destroyed (conservation) • Defined in terms of ampere • Measured in coulomb (C) = As

  5. Representing current • numerical value (+ unit) (e.g., -13.5 A) • direction ( ) • unit is the ampere (A) • represented by I, i, i(t) Symbol for an independent current source Basics - Current • Charge in motion • transfer of energy • related to charge

  6. Basics - Current • Example (a,b) Incomplete, improper, and incorrect definitions of a current. (c) the correct definition of i1(t).

  7. A general two-terminal circuit element Basics - Voltage • General, simple circuit element • two terminals • cannot be decomposed further • completely characterized by itsvoltage-current relationship • Pushing charge • expenditure of energy • electrical voltage (potential difference) • voltage "across" the element

  8. A general two-terminal circuit element Symbols: (a) DC voltage source;(b) battery; (c) ac voltage source. Basics - Voltage • Voltage measures workrequired to move charge • Representing voltage • numerical value (+ unit) (e.g., -2.5 V) • direction (sense) ( + V - )(left terminal is V volts positive withrespect to the right terminal) • unit is volt (V = J / C) • represented by V, v, v(t)

  9. A general two-terminal circuit element Basics - Power • Power is the rate of energyexpenditure: Voltage * Current • Voltage defined in terms of energy • Current is rate at which charge moves • Representing power • numerical value (+ unit) (e.g., -5.6 W) • "direction" by Passive Sign Convention • PSC: Current entering element through positive terminal • unit is watt (W = V *A = J / C *A = J / (As) *A = J / s) • represented by P, p, p(t)

  10. Basics - Passive sign convention (PSC) • Is a choice we make (convention) • The current arrow is directedinto the "+" marked terminal • The power absorbed by the elementis given by the product p = v i • A negative value indicates that poweris actually generated • Or: The power generated by theelement is given by the product p = - v i A general two-terminal circuit element, p = vi represents the power absorbed

  11. Basics - Resistor • Resistance of conducting element • Ohm's law: v = R i • linear, directly proportional • Passive element • Power p = v i = i2 R = v2 / R • Representing resistance • numerical value (+ unit) (e.g., 3 ) • unit is ohm ( = V / A) • represented by R

  12. Circuits • Nodes • Branches • Paths • Loops (a) A circuit containing three nodes and five branches. (b) Node 1 is redrawn to look like two nodes; it is still one node.

  13. Circuits - KCL • Kirchhoff's current law • Conservation of charge The algebraic sum of the currents entering any node is zero. iA + iB - iC - iD = 0

  14. Circuits - KVL • Kirchhoff's voltage law • Conservation of energy The algebraic sum of the voltages around any closed path is zero. v1 = v2 - v3

  15. Circuits - Sources (a) Series connected voltage sources can be replaced by a single source. (b) Parallel current sources can be replaced by a single source.

  16. Circuits - Sources Examples of circuits with multiple sources, some of which are “illegal” as they violate Kirchhoff’s laws.

  17. (a) Series combination of N resistors. (b) Electrically equivalent circuit. Req = R1 + R2 + ... + RN V-I Laws: Resistors

  18. (a) Parallel combination of N resistors. (b) Electrically equivalent circuit. 1/Req = 1/R1 + 1/R2 + ... + 1/RN A special case worth remembering is V-I Laws: Resistors

  19. An illustration of voltage division. Voltage division Using KVL and Ohm's law to find v2. For a string of N series resistors ....

  20. An illustration of current division. Current division Using KCL and Ohm's law to find i2. For a parallel combination of N resistors the current through Rk equals ....

  21. Simplifying circuits (KVL) • What do we count as positive? • Direction of summation determines polarity 1st choice V1 = Va - Vb + Vc 2nd choice V2 = -Va + Vb - Vc

More Related