Rowan Hall 238A

beard@rowan.edu

http://rowan.jkbeard.com

September 11, 2006

Networks I for M.E.ECE 09.201 - 2

James K. Beard, Ph.D.

Slide 2

Voltage The voltage across an element is the work

(energy) required to move a unit positive charge from the - terminal to the + terminal.

a b

ba

+ vab -

- vba + baab vv dq

dwv

Slide 3

Power Power is the time rate of expending energy. Power absorbed by an element is positive, Power delivered by an

element is negative.

a b

ba

+ vab -

- vba +

i

i

ivdt

dq

dq

dw

dt

dwp

Slide 4

Learning Check #6

If 6V (volts) is dissipated across a resistor in which the current is 2A (amperes) what is the power used in watts?

Slide 5

Passive Sign Convention (PSC) Positive current flows from positive

voltage to negative voltage.

a b

- vab +i

ba

+ vab -

i

Is the current in

this resistor positive

or negative?

Is the current in

this element positive

or negative?

Slide 6

Learning Check #7

PSC: positive current flows from positive voltage to negative voltage.

a b

- vab +i

ba

+ vab -

i

If i is positive, does

this conform with PSC?

If i is positive, does

this conform with PSC?

Slide 7

Passive Sign Convention (PSC)

Positive current flows from positive voltage to negative voltage.

a b

- vab +i

ba

+ vab -

i

Is the current in

this resistor positive

or negative?

Is the current in

this element positive

or negative?

Slide 8

Power and PSC

p = v • i Power is absorbed by an element adhering to the

passive sign convention (sink)

Power is supplied by an element not adhering to the passive sign convention (source)

a b

+ vab -i

a b

- vab +i

Slide 9

Power And PSC Example

What is the power absorbed or supplied by the element below, when i = 4A?

Power = 12V x 4A = 48 W Does not adhere to passive sign convention, so power is supplied.

a b

- vab = 12V +i

Slide 10

Power and PSC Quiz

What is the power absorbed or supplied by the element below, when i = -2A?

Power = -12V x -2A = 24 W Does adhere to passive sign convention,

so power is absorbed.

a b

- vab = 12V +i

Slide 11

Power and Energy

p = v • i power = voltage * current (units = watts)

power is the time rate of expending energy

energy = power * time (units = Joules [w-s])

Energy is the capacity to do work

t

pdtw0

Slide 12

Power and Energy

energy = force x distance

power = energy / time period (secs)

Slide 13

Power and Energy Example

A mass of 300 grams experiences a force of 200 newtons. Find the energy (or work expended) if the mass moves 15 cm. Also find the power if the move is completed in 10 milliseconds.

energy = force x distance (N • m) energy = 200 x .15 = 30J power = energy / second (J/sec=Watts) power = 30J/10-2 sec = 3000W = 3kW

Slide 14

Power and Energy Quiz

A Motorola StarTAC cellular phone uses a small 3.6V lithium ion battery with nominal stored energy of 200 joules. For how long will it power the phone if it draws a 3-mA current when in operation?

Slide 15

Quiz Solution

200 joules = 200 watt-secs 3.6 V x 3 mA = 1.08 x 10-2 watts 200 watt-secs / 1.08 x 10-2 watts =

18,519 seconds

18,519 seconds / 3600 sec/hr =

5.1 hours

Slide 16

Learning Check #8

Your iPod shuffle uses a small 3.7V polymer lithium battery with stored energy of 11,322 joules. How many hours will it play tunes if it draws 70.81mA current when in operation?

Slide 17

Voltmeters and Ammeters

DC current and voltage measurements are made with (analog or digital type) ammeters and voltmeters

Voltage measurements are made with red probe (+) at point a, and black probe (-) at point b

a b

+ vab -i

Slide 18

Voltmeters and Ammeters

Current measurements require breaking into the circuit so the ammeter is in series with the current flow (or an expensive inductive pickup)

Made with red probe (+) at point b, and black probe (-) at point c

a bc

+ vab -i

Slide 19

Ideal Meters

Ammeters – negligible voltage drop through it

Voltmeters – negligible current flows into it

Slide 20

Circuit Analysis and Design Analysis – concerned with the

methodological study of a circuit to determine direction and magnitude of one or more circuit variables (V, A) Problem statement Situation and assumptions Goal and requirements Plan act verify if correct, solved If not, plan act verify iterate as needed

Slide 21

Homework for next Tuesday

See next slide for Assignment #1 Show all work for any credit Dorf & Svoboda, pp. 16-18, pp. 44-45 Begin Lab HW Assignment 1

Slide 22

Assignment 1

Due Tuesday, September 19, 8:00 AMDorf & Svoboda, pp. 16-18

Problems 1.2-1, -4, -6 1.5-2, -3, -8 1.7-1

Dorf & Svoboda, pp. 44-45 Problems

2.2-1, -2, -4 2.4-1, -2, -3, -5

NOTE: Show ALL WORK for credit

Slide 23

Lab Homework Assignment 1

Due Monday, September 11, 12:15 PM Lab report due Monday, September 18, 12:15 PM Complete all four (4) MentorGraphics tutorials linked to

http://users.rowan.edu/~jansson/autumn06/Networks1/tutorial.html In the last tutorial (Accusim) you will generate a DC Power Report

for the circuit you build and saved in the Design Architect tutorial. Print out this DC Power Report and turn it in at the beginning of the

next lab meeting on September 11. Show that you personally have completed each step by the

appropriate number of “Snapshot” pictures added to your report. Complete the Matlab tutorial linked to the same page and include at

least three (3) screen snapshots to show that you completed the work.

Log on using your Elvis AccountFor assistance please see Mr. Al Capuano (capuano@rowan.edu)