1 / 21

# EE 221 Review 1 - PowerPoint PPT Presentation

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

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

## PowerPoint Slideshow about ' EE 221 Review 1' - lee-hewitt

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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

### EE 221 Review 1

Basic components

Electric circuits

Voltage and current laws

• 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

• 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

• Example

(a,b) Incomplete, improper, and incorrect definitions of a current. (c) the correct definition of i1(t).

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

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)

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)

• 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

• 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

• 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.

• Kirchhoff's current law

• Conservation of charge

The algebraic sum of the currents

entering any node is zero.

iA + iB - iC - iD = 0

• Kirchhoff's voltage law

• Conservation of energy

The algebraic sum of the voltages

around any closed path is zero.

v1 = v2 - v3

(a) Series connected voltage sources can be replaced by a single source.

(b) Parallel current sources can be replaced by a single source.

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

(a) Series combination of N resistors.

(b) Electrically equivalent circuit.

Req = R1 + R2 + ... + RN

V-I Laws: Resistors

(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

Voltage division

Using KVL and Ohm's law to find v2.

For a string of N series resistors ....

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 ....

• What do we count as positive?

• Direction of summation determines polarity

1st choice

V1 = Va - Vb + Vc

2nd choice

V2 = -Va + Vb - Vc