chapter 1 basics of electricity and theory ppt.pdf

Detail the basics of electricity and basic elements, electrucal quantities and theory on electrucal systems

1. Chapter 1
Basic Concept
2
What is Electricity?
nThe controlled flow of electrons in an
electrical circuit.
nA circuit must always be a complete
loop.
Building Blocks
nAtoms
nNucleus
nProtons (+)
nNeutrons
nElectrons (-)

3
Circuit Essentials
nSource – Battery and Alternator
nPath – Wires or Chassis
qWire size determine amp flow
qWire measure in gauge (AWG)
qBigger gauge = smaller wire
nLoad – The device the electricity runs:
motors, lamps, sensors, relays or
electronic devices.
4/20
Introduction to Electric Circuits
nAn electric circuit is an interconnection of
electrical elements.

nFunctions:
qTo transfer energy from one point to another.

nBasic concepts:
qCharge.
qCurrent.
qVoltage, Resistance ,indeuctance
qPower.
qElectrical field.
qEnergy.

2. 5/20
Charge – q(t)
nBasic quantity in an electric circuit.

nDefined as an electrical property of materials.
qExist as negative (electron) and positive (proton)
charges.
qMeasured in Coulombs (C).
q1 electron = -1.602*10
-19
C.

nPositive and negative charges move in
different direction.
qCreates electric current.
qConsider electric current as movement of positive
charge.

nCharge may be constant/varying.
Charge – q(t)

Question:

nHow much charge is represented by
4,600 electrons?

6/20
Charge – q(t)
7/20
Solution:

Each electron has −1.602 × 10
−19
C.
Hence 4,600 electrons will have
−1.602 × 10
−19
C/electron × 4,600
electrons = −7.369 × 10
−16
C.

8/20
Current – i(t)
nDefined as the charge flow rate.

nMeasured in Ampere (A).

nCurrent may be constant/varying.

3. Current – i(t)
nAn electric current is a flow of
electric charge.
nIn electric circuits this charge is often
carried by moving electrons in a wire.
n It can also be carried by ions in an
electrolyte, or by both ions and
electrons such as in a plasma
9/20
current
nDirect current
qCars
qBatteries
nAC - households
qAlternating current

10/20
Current flow
11/20 12/20
Voltage – v(t)
qWe define voltage as the amount of
potential energy between two points on a
circuit.
qEnergy required to move a unit charge
through an element.
q Measured in volts (V).
Voltage may be constant/varying.
n1 volt = 1 joule/coulomb = 1 newton
meter/coulomb
nVoltage, ,

4. Resistance
nThe electrical resistance of an electrical
conductor is a measure of the difficulty to pass
an electric current through that conductor.
nOpposition to the flow of current
nThe resistance (R) of an object is defined as the
ratio of voltage across it (V) to current through it
(I), while the conductance (G) is the inverse:


13/20 14
Resistance is affected by .
. .

nDiameter of the wire
nTemperature of the wire
nLength of the wire
nMaterial wire if made from
Inductance and inductor
ninductance is the property of an electrical
conductor by which a change in current flowing
through it induces an electromotive force in both
the conductor itself and in any nearby conductors
by mutual inductance.
nTo store magnetic energy
nThe element which uses to store magnetic energy
is called inductor
nIt use the symbol L for inductance.
nthe SI system the measurement unit for
inductance is the henry with the unit symbol H
15/20
Capacitance and capacitor
ncapacitance is the property of an electrical
conductor by which a change in voltage flowing
through it induces a current in both the
conductor itself and in any nearby conductors by
mutual capacitance.
nCapacitance Is the ability to store electric energy.
nThe element which uses to store electric energy
is called capacitor.
nIt use the symbol C for capacitance.
nthe SI system the measurement unit for
capacitance is the farad with the unit symbol F


16/20

5. 17/20
Power – p(t)
nDefined to be the time rate of expending or
absorbing energy.
qMeasured in watts (W).

nPower can be absorbed or supplied by circuit
elements.
qPositive power а element absorbs power.
qNegative power а element supplies power.
q‘Sign’ determined by voltage and current.

nAn ideal circuit:
q∑P
supplied
+ ∑ P
absorbed
= 0.


18/20
Energy
nDefined as the capacity to do work.
nElectrical energy is energy that's
stored in charged particles within an
electric field.

nMeasured in joules (J).
Example:
nAn energy source forces a constant
current of 2 A for 10 s to flow through a
lightbulb. If 2.3 kJ is given off in the
form of light and heat energy, calculate
the voltage drop across the bulb.
19/20
Solution
20/20

6. Electric fields
nElectric fields are simply areas
surrounding a charged particle.
nIn other words, charged particles create
electric fields that exert force on other
charged particles within the field
nThe electric field applies the force to
the charged particle, causing it to move
- in other words, do work.
21/20 22/20
Electric fields point in the direction that positive
particles would move within them
23/20
Circuit Elements
nAn element is the basic building block of a
circuit.

nElectric circuit is interconnecting of the
elements.

nTypes of elements:
qActive elements аCapable of generating energy
(i.e. batteries, generators).
qPassive elements а Absorbs energy (i.e. resistors,
capacitors and inductors).
qVoltage and current sources а the most important
active elements.

24/20
Source
nDivided into:
qIndependent source а Does not depend to
other elements to supply voltage or current.
qDependent source а Reverse of
independent.

nConstant voltage source:
qVoltage same for all elements.

nConstant current source:
qCurrent same throughout the circuits.

7. 25/20
Examples


nCalculate the amount of charge represented
by two million protons.

nAnswer: +3.204 × 10
−13
C.