Electricity

INTRODUCTION
to

ELECTRICITY

ELECTRICITY

Movement of electrons……. Invisible force that provides light, heat, sound, motion . .

Introduction to Electricity - Lecture by Uma Jadhav

2

12/21/2012

Atoms
Smallest piece of an element containing all of the properties of that element

Introduction to Electricity - Lecture by Uma Jadhav

3

12/21/2012

 A very highly simplified model of an atom has most of the mass in a small,

dense center called the nucleus.  The nucleus has positively charged protons and neutral neutrons.  Negatively charged electrons move around the nucleus at much greater distance.  Ordinary atoms are neutral because there is a balance between the number of positively charged protons and negatively charged electrons.

Introduction to Electricity - Lecture by Uma Jadhav

4

12/21/2012

Electricity at the Atomic Level
Components of an Atom
Nucleus
 The center portion of an atom

containing the protons and neutrons particles

Protons
 Positively charged atomic

Neutrons
 Uncharged atomic particles

Atomic Number:
The atomic number is equal to the number of protons in the nucleus of an atom.
Introduction to Electricity - Lecture by Uma Jadhav

5

12/21/2012

Electricity at the Atomic Level
Electrons
Negatively charged particles

Electron Orbitals

Orbits in which electrons move around the nucleus of an atom

2D 3D

Valence Electrons

The outermost ring of electrons in an atom
6
12/21/2012

Introduction to Electricity - Lecture by Uma Jadhav

Electricity at the Atomic Level
Electron Orbits  Atoms like to have their valence ring either filled (8) or empty(0) of electrons.
Copper

Cu
29

Electrons in Valence

Conductor / Insulator

01

Conductor

 An electron from one orbit can knock out an electron

from another orbit.  When an atom loses an electron, it seeks another to fill the vacancy.
Introduction to Electricity - Lecture by Uma Jadhav

7

12/21/2012

Electricity at the Atomic Level
Electron Flow:  Electricity is created as electrons collide and transfer from atom to atom.

Electrostatic Charge:
• Electrons move from atom to atom to create ions. • positively charge ions result from the loss of electrons and are called cations. • Negatively charge ions result from the gain of electrons and are called anions.
Introduction to Electricity - Lecture by Uma Jadhav

8

12/21/2012

Electric Charge & Electrical Forces:
 

Electrons have a negative electrical charge. Protons have a positive electrical charge.

These charges interact to create an electrical force.


Like charges produce repulsive forces – so they repel each other (e.g. electron and electron or proton and proton repel each other). Unlike charges produce attractive forces – so they attract each other (e.g. electron and proton attract each other).
9
12/21/2012



Introduction to Electricity - Lecture by Uma Jadhav

What is Electricity?
 Electricity is the presence and motion of charged

particles.
 Electric Current is a flow of charged particles

around an closed path – an electric circuit.

Introduction to Electricity - Lecture by Uma Jadhav

10

12/21/2012

Electrical Conductor And Insulators
• Electrical conductors are materials that can move • •
electrons easily. Good conductors include metals. Copper is the best electrical conductor. Electrical nonconductors (insulators) are materials that do not move electrons easily. Examples are wood, rubber etc. Semiconductors are materials that sometimes behave as conductors and sometimes behave as insulators. Examples are silicon, arsenic, germanium.
11
12/21/2012

Introduction to Electricity - Lecture by Uma Jadhav

Insulator
Electron Orbits  Atoms like to have their valence ring either filled (8) or empty(0) of electrons.
Sulfur
Electrons in Valence Conductor / Insulator

S
16

06

Insulator

Introduction to Electricity - Lecture by Uma Jadhav

12

12/21/2012

Introduction to Electricity - Lecture by Uma Jadhav

13

12/21/2012

Conductor & Insulators
Sr. No. Conductor Insulator

1 2
3 4

Electrons flow easily between atoms 1-3 valence electrons in outer orbit Have low resistance against current Examples: Silver, Copper, Gold, Aluminum

Electron flow is difficult between atoms 5-8 valence electrons in outer orbit Have high resistance against current Examples: Mica, Glass, Quartz
14
12/21/2012

Introduction to Electricity - Lecture by Uma Jadhav

Conductor & Insulators

Conductors

Insulators

Introduction to Electricity - Lecture by Uma Jadhav

15

12/21/2012

Electrical Circuit
Electrical circuit is a system of conductors and components forming a complete path for current to travel Properties of an electrical circuit include
Quantities Voltage Abbreviations V Units Volts Symbols V

Current
Resistance

I
R

Amperes
Ohms

A
Ω

All electrical circuits have three parts in common. • A voltage source. • An electrical device • Conducting wires.
Introduction to Electricity - Lecture by Uma Jadhav

16

12/21/2012

The Electrical Circuit
An electrical circuit contains some device that acts as a source of energy as it gives charges a higher potential against an electrical field. • The charges do work as they flow through the circuit to a lower potential. • The charges flow through connecting wires to make a continuous path. • A switch is a means of interrupting or completing the circuit. The source of the electrical potential is the voltage source.

Introduction to Electricity - Lecture by Uma Jadhav

17

12/21/2012

Current & Current In A Circuit
Current: The flow of electric charge or The charge flowing through a point per unit time
Unit: AMPERES (A) Types: • Direct Current (DC) • Alternating Current (AC)
off on

 When the switch is off, there is no current.  When the switch is on, there is current.
Introduction to Electricity - Lecture by Uma Jadhav

18

12/21/2012

Voltage & Voltage In A Circuit

 The force (pressure) that

causes current to flow
Unit: VOLTS (V)
off on

 The battery provides voltage that

will push current through the bulb when the switch is on.
Introduction to Electricity - Lecture by Uma Jadhav

19

12/21/2012

Resistance & Resistance In A Circuit
 The opposition of current

flow Unit: Ohms (Ω)
 Resistors are components
off on

that create resistance.
 Reducing current causes the

bulb to become more dim.
Introduction to Electricity - Lecture by Uma Jadhav

20

12/21/2012

The magnitude of the electrical resistance of a conductor depends on four variables: • The length of the conductor. • The cross-sectional area of the conductor. • The material the conductor is made of. • The temperature of the conductor.

Introduction to Electricity - Lecture by Uma Jadhav

21

12/21/2012

Current & Resistance

 Current is the flow of the outer electrons of atoms

through the material.
 Resistance then results from the collisions of

electrons with other electrons and with atoms.

Introduction to Electricity - Lecture by Uma Jadhav

22

12/21/2012

Symbols

Voltage

V

Current
Resistance
Introduction to Electricity - Lecture by Uma Jadhav

I
R
12/21/2012

23

Ohm’s Law
 In an Electrical circuit, the current passing through a

conductor between two points is directly proportional to the potential difference across the two points (providing physical conditions remain constant).
 The mathematical relationship between current,

voltage, and resistance

V=IR I=V/R R=V/I
Introduction to Electricity - Lecture by Uma Jadhav

24

12/21/2012

Example
 The flashlight shown uses a 6 volt battery

and has a bulb with a resistance of 150 . When the flashlight is on, how much current will be drawn from the battery?
IR
+ -

Schematic Diagram

VT =

VR

Introduction to Electricity - Lecture by Uma Jadhav

25

12/21/2012

Example
 The flashlight shown uses a 6 volt battery

and has a bulb with a resistance of 150 . When the flashlight is on, how much current will be drawn from the battery?
IR
+ -

Schematic Diagram

VT =

VR

VR 6V IR    0.04 A  40 mA R 150 
Introduction to Electricity - Lecture by Uma Jadhav

26

12/21/2012

Circuit Configuration
 Components in a circuit can be connected in one of two

ways.
Series Circuits
Components are connected end-to-end.

Parallel Circuits
Both ends of the components are connected together.

There is only a single path for current to There are multiple paths for current to flow. flow.

Components
(i.e., resistors, batteries, capacitors, etc.) Introduction to Electricity - Lecture by Uma Jadhav

27

12/21/2012

Series Circuits
 A circuit that contains only one path

for current flow  If the path is open anywhere in the circuit, current stops flowing to all components. Characteristics of a series circuit  The current flowing through every series component is equal.  The total resistance (RT) is equal to the sum of all of the resistances (i.e., R1 + R2 + R3).  The sum of all of the voltage drops (VR1 + VR2 + VR3) is equal to the total applied voltage (VT). This is called Kirchhoff’s Voltage Law.
Introduction to Electricity - Lecture by Uma Jadhav

28

12/21/2012

Example: Series Circuit
For the series circuit shown, use the laws of circuit theory to calculate the following:
The total resistance (RT) The current flowing through each component (IT, IR1, IR2, & IR3) The voltage across each component (VT, VR1, VR2, & VR3) Use the results to verify Kirchhoff’s Voltage Law.
IT + VR1 -

+ VT

IR1
IR2

+
VR2 -

-

IR3

RT
Introduction to Electricity - Lecture by Uma Jadhav

-

+

VR3

29

12/21/2012

Solution
Total Resistance:
RT=R1 +R2+R3 RT= 220Ω + 470 Ω=1.2k Ω (1200 Ω) RT = 1900 Ω = 1.9 kΩ

Current Through Each Component: V 12 v IT  T (Ohm's Law) IT   6.3 mAmp RT 1.89 k

Since this is a series circuit: IT  IR1  IR2  IR3  6.3 mAmp
Voltage Across Each Component:
VR1  IR1  R1  (Ohm's Law)
VR2  IR2  R2 (Ohm's Law)
VR2  6.349 mA  470 Ω  2.984 volts

VR1  6.349 mA  220 Ω  1.397 volts
VR3  IR3  R3 (Ohm's Law)
VR3  6.349 mA 1.2 K Ω  7.619 volts
Introduction to Electricity - Lecture by Uma Jadhav

VT  VR1  VR2  VR3
30
12/21/2012

Parallel Circuits
 A circuit that contains more than one

path for current flow  If a component is removed, then it is possible for the current to take another path to reach other components. Characteristics of a Parallel Circuit  The voltage across every parallel VT component is equal.  The total resistance (RT) is equal to the reciprocal of the sum of the reciprocal:  The sum of all of the currents in each branch (IR1 + IR2 + IR3) is equal to the total current (IT). This is called Kirchhoff’s Current Law.
Introduction to Electricity - Lecture by Uma Jadhav

IT

+
-

+
VR1 -

+
VR2 -

+
VR3 -

RT

31

12/21/2012

Example Parallel Circuits
For the parallel circuit shown, use the laws of circuit theory to calculate the following: The total resistance (RT) The voltage across each component (VT, VR1, VR2, & VR3) The current flowing through each component (IT, IR1, IR2, & IR3) Use the results to verify Kirchhoff’s Current Law.
IT
IR1 + + VR1 VR2 + VR3 IR2 + IR3

VT

-

-

-

32 RT
Introduction to Electricity - Lecture by Uma Jadhav

32

12/21/2012

Solution
Total Resistance:
RT  1 1 1 1   R1 R2 R3

RT 

1 RT  346.59 = 350  1 1 1   470  2.2 k 3.3 k

Voltage Across Each Component:
Since this is a parallelcircuit : VT  VR1  VR2  VR3  15 volts

Current Through Each Component:
V IR1  R1 R1 (Ohm's Law)

VR1 15 v   31.915 mA=32 mA R1 470  V 15 v IR2  R2   6.818 mA = 6.8 mA R2 2.2 k  V 15 v IR3  R3   4.545 mA= 4.5mA R3 3.3 k  IR1 
IT  VT RT  15 v  43.278 mA = 43 mA 346.59  33

IT  IR1  IR2  IR3

Introduction to Electricity - Lecture by Uma Jadhav

12/21/2012

Combination Circuits
 Contain both series and parallel arrangements

1

2

3

Introduction to Electricity - Lecture by Uma Jadhav

34

12/21/2012

Electrical Power
 Electrical power is directly related to the amount of

current and voltage within a system.  Power is measured in watts

P  I V

Introduction to Electricity - Lecture by Uma Jadhav

35

12/21/2012

References
 Microsoft, Inc. (2008). Clip Art. Retrieved November 20, 2008, from

http://office.microsoft.com/en-us/clipart/default.aspx  http://www-outreach.phy.cam.ac.uk/workshop/Mar2008/resources/Intro.pdf  learn.kalida.k12.oh.us/mod/resource/view.php?id=259&redirect..  augusta.k12.wi.us/HS/dept/sci/.../Electricity%20&%20Magnetism.ppt

Introduction to Electricity - Lecture by Uma Jadhav

36

12/21/2012