Fundamentals of electric circuits

MY PROFILE Name : Abdullah Al Mahfuj

Department : Textile.

Program : B.Sc. in Textile Engineering .

ID : 142014007

Green University of Bangladesh

Name of My Presentation

FUNDAMENTALS OF ELECTRIC CIRCUITS

PRINCIPAL ELEMENTS OF ELECTRICAL CIRCUITS

INDEPENDENT SOURCES The voltage/current sources that have the capability of

generating a prescribed voltage or current independent of any other element within the circuit.

These sources may output a constant voltage/current, or they may output voltage/current that varies with time.

1) Ideal Voltage Sources

An ideal voltage source is a two-terminal element that maintains the same voltage across its terminals regardless of the current flowing through it.

Vt = constant, no matter what the load current is.

Vt

IL

Vo

L

t

+

-

Vo

2) Ideal Current Sources

An ideal current source is a two-terminal element that maintains the same current regardless of the voltage across its terminals.

IS = constant, no matter what the load voltage is.

IO

VO

IS

DEPENDENT (CONTROLLED) SOURCES

Dependent sources are whose output (current or voltage) is a function of some other voltage or current in a circuit.

The symbols typically used to represent dependent sources are in the shape of a diamond.

BRANCH, NODE, LOOP, MESH

Branch : any portion of a circuit with two terminals connected to it.

A branch may consist of one or more circuit elements.

Node : the point of connection between two or more branches.

A node usually indicated by a dot in a circuit.

Loop : any closed path through the circuit in which no node is encountered more than once.

Mesh : a loop that does not contain other loops.

CURRENT AND KIRCHHOFF’S CURRENT LAW

Electric Current Electric current is defined as the time rate of change of

charge passing through a predetermined area.

The units of current are called Amperes, where 1 Ampere (A) = 1 Coulomb/second (C/s). In order for current to flow, there must exist a closed circuit.

EEE 1012 INTRODUCTION TO ELECTRICAL ENGINEERING

• In the circuit of this figure, the current i flowing from the battery to the light bulb is equal to the current flowing from the light bulb to the battery. no current (and therefore no charge) is “lost”

around the closed circuit. This principle is known as Kirchhoff’s current law (KCL).

Kirchhoff’s Current Law (KCL)

One of the fundamental laws of circuit analysis. Establish in 1874 by G.R. Kirchhoff.

“The sum of the currents at a node must equal zero.”

Example of Kirchhoff’s current law:

At node 1:

In this illustration, currents entering a node are defined as negative and currents leaving the node as positive.

VOLTAGE AND KIRCHHOFF’S VOLTAGE LAW

Voltage The total work per unit charge associated with

the motion of charge between two points. The units of voltage are called Volts, where 1 Volts (V) = 1 Joule (J)/Coulomb (C).

Kirchhoff’s Voltage Law (KVL)

The second fundamental laws of circuit analysis introduced by G.R. Kirchhoff.

The principle underlying KVL is that no energy is lost or created in an electric circuit.

In circuit terms, the sum of all voltages associated with source must equal the sum of the load voltages.

“The net voltage around a closed circuit is zero.”

Example of Kirchhoff’s voltage law:

where

In general, elements that provide energy are referred as sources and elements that dissipate energyas loads.

ELECTRIC POWER

Power The electric power generated by an active element, or that

dissipated or stored by a passive element, is equal to the product of the voltage across the element and the current flowing through it.

The units of power are called Watts (Joules/second).

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MEASURING DEVICES

Ohmmeter:The ohmmeter is a device

that, can measure the resistance of the element.

AmmeterThe ammeter is a device that can

measure the current flowing through the element.

VoltmeterThe voltmeter is a device that can

measure the voltage across a circuit element.