- 110 Views
- Uploaded on

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

**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.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

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

- 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

Basics - Current

- 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)

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

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

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.

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

Circuits - KVL

- Kirchhoff's voltage law
- Conservation of energy

The algebraic sum of the voltages

around any closed path is zero.

v1 = v2 - v3

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.

Circuits - Sources

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: ResistorsAn illustration of voltage division.

Voltage divisionUsing KVL and Ohm's law to find v2.

For a string of N series resistors ....

current division.

Current divisionUsing KCL and Ohm's law to find i2.

For a parallel combination of N resistors

the current through Rk equals ....

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

Download Presentation

Connecting to Server..