• Charge Q (C); Current I (A); Voltage V (V)
• Power P (W)
• Reference directions

• Basic concepts (1)

Form of Energy

‘

• lnterco lJfl of electrical elements using conducting wires • Used i
‘erous electrical systems (often with other non electrIc& systems), to accomplish different tasks
• Circuit A ayss understand circuit behaviour, interactv between elements, system response, etc.

Electric& ircuits

Laws eri rIations that govern fundamentals, uses, and convers’ n o other forms of energy (heat, light, sound or mechana energies) were discovered over last 300 yrs
• Electric[ f. ctronics is used in one form or another in almost an modern day activities

Electricity

Electrical Circuits

—

—

• F ud/thermaI exchange in mechanical
4 )tems
• C hemical exchange in biological systems

• Not just fundamental to all branches of electrical engineering
Qut€ important for many branches in the physical sciences
Circuits are a good model for the study cnergy systems in general

Why study electrical circuits?

-

Chapter 1

L2 Systems of Units.
13 Electric Charge.
14 Current.
15 Voltage.
16 Power and Energy.
1.7 Circuit Elements.

Basic Concepts

a

meter kilogram second ampere kelvin
Coulomb

Length
Mass

Fime

Electric current

Thermodynamic temperature (Th arge

Basic unit

C

K

A

s

Kg

m

Symbol

System of Units (1)

Six basic units
Quantity

a

L2

Unit

coulomb volt ohm siemens henry farad hertz newton joule watt weber tesla Quantity

electric charge electric potential resistance conductance inductance capacitance frequency force energy, work power magnetic flux magnetic flux density
C
V fl S
H
F
Hz
N
3
W
Wb
T

Symbol

micro nano pico

10_6

2
1W’

iO

milli

giga mega kilo centi Prefix

i0

i0
10—2

106

1O

Factor

:i

i ‘It)

n p M k c m 0

Symbol

I units commonly used in electric circuit theory

12 System of Units (2)

-

-

—

-

outer most orbit weak binding force valence bands easily escape with little energy

on a single proton

Charge on a single electron is equal and opposite to that

-

-

-

-

Negatively (-) charged

Free electrons

Positvely (+) charged

particles of which matter exists
Most basic quantity in an electric circuit
Atom: Nucleus (Protons, Neutrons) + Electrons

Definition the electrical property of certain subatomic

13 Electric Charge

t

)

-ye
+

=e

move towards

ec move towards +ve

Under the influence of external energy source (eg. battery)

Metals like copper aluminum, sliver, gold 4 electrons in valence band
4
even at room temp. 4 free electrons

-

=

charge on 6.242 X ictrons eie d
8

f

g. Charge can neither be created nor de stroyed, only transferred

on one electron is and equal in magnitude to which is called as electronic charge. Th e charges that occur in nature are i of the electronic charge

The charge

Unit charge of 1 coulomb (C)

4 Unit for charge 4 French Scientist

L3 Units of Charge:

a) 6482

*

I ()

How many coulombs are represented by these amount of electrons?

Ex 1:

Example Problem 1

c

C

cj
%J

0

a

-r

7e

cJ

0

-

_

Is

0 a U
II

a a3JQ U

11

ci)

a —

U, a cL,

0
>0(
a—

D

U
U

—U

E

•

(t3

U
4J

C

0

U

D
U

E

0

ci)

Ii

C

E
1-J

U

I

a,
0

Z3
C&

(0

I’

-

0 ci a,

0
0
0

2

ci

11

2°

a, a, 0

E czs rO2

a, ci 0

I’

I

urrent (cic) is a current that

=

5A

t(s)

0

I

4

T

t

I2A
I=-2A

remains constant with times
• An iinq curwnt (ac) is a current that varies sinusoidally with times
(reverse direction)

• AdL

13 Electric Current

5

How many