1

CIRCUIT ANALYSIS

ENGR. VIKRAM KUMAR

B.E (ELECTRONICS)M.E (ELECTRONICS SYSTEM ENGG:)MUET JAMSHORO

OHM’S LAW

2

AMPS

volts

Ammeters measurecurrent in amperes

and are alwayswired in series in

the circuit.

Voltmeters measurepotential in voltsand are always

wired in parallel in the circuit.

3

wiring

battery

voltmeter

ammeter

resistance

capacitor

+ -

A

V

junction

terminal

AC generator

Variableresistance

Variablecapacitor

4

ELECTRON PUMP

(SOURCE VOLTAGE)[ENERGY IN]

LOAD(RESISTANCE)

[ENERGY OUT]

CONDUCTOR

ELECTRONSOUT OF SOURCE

ELECTRONSOUT OF LOAD

ELECTRONSBACK TOSOURCE

ELECTRONSINTOLOAD

HIGHER ENERGY ELECTRONS LOWER ENERGY ELECTRONS

CONDUCTOR

5

PotentialIn volts

(joules / coul)

CurrentIn amperes

(coul / second)

ResistanceIn ohms

(volts / amp)

Drop across a resistance

Current passingThrough the

resistor

6

volts

Batterycurrent

Electrons haveLess Energy

Electrons haveMore Energy Electrons get

An energy boost

current

7

volts

Resistor current

Electrons haveMore Energy

Electrons haveLess Energy Energy is lost

In the resistor

4.2 - Ohm’s Law

Every conversion of energy from one form to another can be related to this equation.

In electric circuits the effect we are trying to establish is the flow of charge, or current. The potential difference, or voltage between two points is the cause (“pressure”), and resistance is the opposition encountered.

OppositionCause

Effect

9

Ohm’s Law

Simple analogy: Water in a hose Electrons in a copper wire are analogous to water in

a hose. Consider the pressure valve as the applied voltage

and the size of the hose as the source of resistance. The absence of pressure in the hose, or voltage across

the wire will result in a system without motion or reaction.

A small diameter hose will limit the rate at which water will flow, just as a small diameter copper wire limits the flow of electrons.

Ohm’s Law

Where: I = current (amperes, A)E = voltage (volts, V)R = resistance (ohms, )

RE

I

11

4.3 - Plotting Ohm’s Law

12

There are three generally types of electrical circuits:

(1) Series circuits in which the current created by the voltagesource passes through each circuit component in succession.

R2 A2

R 1

R 3

A1

Arrows showCurrent pathThrough eachcomponent

13

(2) Parallel circuits in which the current created by the voltagesource branches with some passing through one component andwhile the rest of the current passes through other components.

Arrows showCurrent pathThrough eachcomponent

Junction or Branching points

A1R1

R2

R3

A2

A3

A4

R 4

14

(3) Series Parallel circuits or combination circuits which contain series segments and parallel

segments.

R1

R2

R3

A1

A2

A3

A4

R 4

SERIES

PARALLEL

Arrows showCurrent pathThrough eachcomponent

15

All electrical circuit analysis requires the useof two fundamental laws called

Kirchhoff’s Laws

16

FIRST LAWAll current entering a junction point must

equal all current leaving that junction point

Junctionpoint

Current Entering ( I1 )

Current Leaving ( I2 )

Current Leaving ( I3 )

I1 = I2 + I3

17

SECOND LAWAround any complete loop, the sum of the

voltage rises must equal the sum of voltage drops

Battery(voltage rise)

Resistance 1(voltage drop 1)

Resistance 2(voltage drop 2)

Resistance 3(voltage drop 3)

Current flow

Complete loop

V(Battery) = V1 + V2 + V3

+ -

18

R2

R1

A2

A1

At

V1

EMF

Kirchhoff’s Laws Around a loop

S V rises = V dropsA loop is a completedPath for current flow

Battery

V2

Loop #1

Loop #2

Loop #3

+ -

Complete currentPaths in a circuit

19

When using Kirchhoff’s laws we apply the principlesof conventional current flow.

When current leaves the positive (+) terminal of a voltage source and enters the negative (-) terminal a voltage rise occurs across the source. If the current

enters the positive and exits the negative a of a voltagesource a voltage drop occurs across the source.

When tracing a current loop, if the assumed directionof the current and the loop direction are the same,

a voltage drop occurs across a resistance.If the assumed direction of the current and the

loop direction are opposite, a voltage rise occursacross the the resistance.

20

Battery( 6 volts)

+ -

CurrentflowV = + 6 v

Currentflow

V = - 6 v

When using Kirchhoff’s laws we apply the principlesof conventional current flow.

When current leaves the positive (+) terminal of a voltage source and enters the negative (-) terminal

a voltage rise occurs across the source.

If the current enters the positive and exits the negative a of a voltage source a voltage drop occurs across

the source.

21

When tracing a current loop, if the assumed directionof the current and the loop direction are the same,

a voltage drop occurs across a resistance.

resistor

V = + 6 vA voltage

rise

AssumedCurrent flow

V = - 6 vA voltage

dropLoop

direction

AssumedCurrent flow

Loopdirection

If the assumed direction of the current and theloop direction are opposite, a voltage rise occurs

across the the resistance.

22