lecture 2 ees512 by karthi

8/14/2019 Lecture 2 EES512 by Karthi

1/15

EES 512 Electric Circuits Fall 2009

Sections - 5, 6, 7, 8

Instructor: Dr. Karthi Umapathy

[email protected]

1EES 512, Fall 2009, KU


2/15

Charge

Current

Voltage or Potential Difference

Power and Energy

Efficiency

Resistance

Conductance

Ohms Law

Previous Lecture


3/15

Measuring Current (through R) and Voltage (across R)

readingammeter

readingvoltmeter

I

VR ==


4/15

Power in a Resistance

External energy source ProvidesWork Overcome Resistance

The work collision mechanism other forms of energy (heat, light)

Resistors can be used for one of the following:

To limit or control the current flow

Energy conversions heat or light or mechanical energy

To connect electrical components

VIt

Q

Q

W

t

WP ===

R

VI =From Ohms law


5/15

Power in a Resistance

R

V

P

2

= RIP2

=or

Resistor dissipate heat energy due to collision mechanisms

Power rating

RPVmaxmax

=

RPI max

max=

Max safe voltage across R

Max safe current across R

Energy dissipated in any resistance or work done = tPW =

tIVW = J


6/15

Ex: Calculate power dissipated

a) V= 12 V , I = 100 mA, R = 120 ohms

b) V= 16.8 V, I = 30 mA, R= 560 ohms

c) V= 10 V, I = 5 mA, R = 2000 ohms

Ans = 1.2 W

Ans = 0.504 W

Ans = 50 mW

Ex:

A 0.25 W, 10 K ohm resistor is available. Find the maximum safe voltage

And the current that can be applied to the resistor without damage

RPVmaxmax

=

R

PI max

max= Ans = 50 V, 5 mA


7/15

Ex:

Find the energy used by a 50 ohm heater element operating from 120 Vsource for 2 hr

R

VP

2

= Ans =0.288 kW x 2 hr = 0.576 kWh

Ex:

Find the resistance of each of the following elements

a) When a 20 V source is applied to the element, it dissipates 0.25 W

b) The element dissipates 50 mW when the current flowing in it is 5 mA

Ans = 1600 ohms

Ans = 2000 ohms


8/15

Graphical Characteristics of Resistors

When a resistor obeys ohms law

it is called a linear resistor

RIV =

Straight liney=mx

VR

GVI1

==


9/15

Graphical Characteristics of Resistors

VR

GVI1

==


10/15

Non-linear elementsDo not obeyOhms law

bkVIn

+=

static resistance = I

VR

dc

=

dynamic resistance =

At any specific operating point

dI

dVrac

= Slope of

tangent


11/15

Ex:The I-V relationship show below for a particular value of R. Draw the I-VRelationship for resistances

a) 3Rb) 0.5 R R

I

V0

1I

1V

1

1

IVR =


12/15

1

1

I

VR =

R

VI

1

1=

R

VI

33

11=

Ans

R

VI

=

5.02

1

1


13/15

Practical Resistors


14/15

Color Coding of Resistors

B B R O Y G B V G W


15/15

DC Circuits

Analysis techniques for simple circuits made up of resistors andDC sources

lecture 2 ees512 by karthi

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