Electronic Basics
Dr. Farid Farahmand
Outline
Reviewing basic concepts: Voltage,
Current, and Resistance
 Ohm’s law
 Power and Energy

Introduction

Electricity is everywhere! But what is it?



Movement of electrons
Electrons move all over the place in a conductor
They glide through like marbles sliding on the floor
Less resistance  More moving
The electrons can move but something must move
them
The force that moves electrons from one place to
another is called voltage

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Electrical Energy


Electrical Energy can be generated from different
forms of energies
Coal, oil, natural gas


Nuclear or solar energy


Creates steam to drive a turbine that generates
electricity.
Creates steam to drive the turbine.
Solar photovoltaic or fuel cells and batteries

Rely upon chemical reactions to generate electricity

Sun Farm Networks
http://www.sunfarmnetwork.com/25647_105755.asp
Electrons
Electricity is due to excess of electrons!
 Smallest molecule is Hydrogen
 Free electrons  Electricity

Atom Structure

An atom is the smallest
particle of an element that
retains the characteristics of
that element.
 An atom has a nucleus,
consisting of positively
charged particles called
protons, and uncharged
particles called neutrons.
 The basic particles of
negative charge, called
electrons, orbit the nucleus.
Voltage



The unit of voltage is the volt (V).
One coulomb is the total charge possessed by 6.25 x
1018 electrons.
Q = (number of electrons)/(6.25 x 1018)
By definition:

One volt is the potential difference (voltage) between two
points when one joule of energy is used to move one coulomb
of charge from one point to the other.
1 Joule of Energy
1C
The potential
difference is one
Volt!
Voltage Sources

A battery is a type of voltage source that
converts chemical energy into electrical
energy.
 Solar Cells convert light energy into electrical
energy.
 Generators convert mechanical energy into
electrical energy.
 Electronic power supplies (voltage
converters)?

They do not produce electrical energy, but they
transform the ac voltage from the wall outlet into a
constant dc voltage for use in our circuits.
Current

Current definition
 The movement of free
electrons from negative to
positive is electrical
current (I).
 Electrical current is the
rate of flow of charge
I = Q/t
One C of
charges/sec

The Unit of Current is Amp
 One amp is the amount
of current that exists
when a number of
electrons having a total
charge of one coulomb
move through a given
cross-sectional area in
one second.
Movement of Electrons
Early experiments appeared as if flow of
electrons is from + voltage to – voltage
 But in reality, flow of electrons is from voltage to + voltage
 When electrons move from -  +
terminals, the flow is called an electric
current
 Voltage is the driving force in electric
circuits and is what establishes current

Current Flow

Current flow can be Direct or Alternating
Direct or DC: Electric flow is only in one
direction
 Alternating or AC: Electric flow is in one
direction and then in another


Property of material that resists the flow
of electrons is called resistance
AC
DC
Resistance



The property of a
material that restricts the
flow of electrons is
called resistance.
The unit of Resistance is
Ohm ().
By definition

One ohm of resistance
exists if there is one
ampere of current in a
material when one volt
is applied across the
material.
Applying 1 V
1 A of current
is generated
There must be 1 ohm of resistance!
Ohm’s Law
Ohm’s law describes
mathematically how voltage,
current, and resistance are
related. I = V/R
Hence, current and voltage are
linearly proportional.

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In resistive circuits, with a
constant resistance, if voltage
increases or decreases by a
certain percentage, so will
current.
On the other hand, current and
resistance are inversely related.

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With constant voltage, if
resistance is reduced, current
goes up; when resistance is
increased, current goes down
Energy and Power

Energy is the ability to do work - joules (J)
 Power is the rate at which energy is used - in
watts (W)
 By definition:
One watt is the amount of power when one
joule of energy used in one second.
Power = energy/time
P = W/t
Kilowatt-hour
The kilowatt-hour (kWh) is frequently
used as a unit of energy. One kWh is
used when one thousand watts is used
for one hour.
 Power utilized over a period of time
represents energy consumption.
W = Pt
 Energy can also be expressed as wattseconds (Ws), watt-hour (Wh).

Power in an Electric Circuit

There is always a certain amount of
power in an electric circuit, and it is
dependant on the amount of resistance
and the amount of current, expressed as:
P=
2
IR
Resistance- Remember



The property of a
material that restricts the
flow of electrons is
called resistance.
The unit of Resistance is
Ohm ().
By definition

One ohm of resistance
exists if there is one
ampere of current in a
material when one volt
is applied across the
material.
Applying 1 V
1 A of current
is generated
There must be 1 ohm of resistance!
Color-code bands on a resistor
1st band is the first digit of the resistance
value.
 2nd band is the second digit of the resistance
value.
 3rd band is the multiplier (number of zeros).
 4th band indicates the tolerance.

Examples: http://www.ccsu.edu/technology/farahmand/ccsu/courses/cet233/cet_233.htm#Resistors
Resistor color code
Ohm’s Law
Given R=10 ohm;
how will this graph look like?
Ohm’s Law
Voltage and Current Measurements


To measure voltage, the
voltmeter is placed in
parallel across the
component; that is, one
lead is place on each
side of the component.
To measure current, the
ammeter must be placed
in series with the
component; that is, it
must be in line with the
current path.
Voltage and Current Measurements


To measure voltage, the
voltmeter is placed in
parallel across the
component; that is, one
lead is place on each
side of the component.
To measure current, the
ammeter must be placed
in series with the
component; that is, it
must be in line with the
current path.
Analyzing the circuit:
Total resistance = 10+15+22+3.3=50.3K
I=V/R = 0.298 mA
What is the measurement error? About %2 error!
Where does the error come from?
What is the measurement error across 15K resistor?
304.2 μ
4.469
6.509
Check the numbers! Make sure
you understand how we got
them!
Current Measurements
304.2 μ
4.469
6.509
Voltage Measurements
304.2 μ
4.469
6.509
DO THIS PRE-LAB:

See the Web site!
LAB

Find the resistance of the giver
resistor using its colors
 Check the calculated value using
a Multi-meter
 Connect two resistors in series
and measure the total resistance
 Connect two resistors in parallel
and measure the total resistance
References
http://people.clarkson.edu/~svoboda/eta/dcWorkout/OandKLawsR.
html
http://people.clarkson.edu/~svoboda/eta/dc
Workout/VandCDividers.html
http://people.clarkson.edu/~svoboda/eta/ec
sa.html - Main page
http://people.clarkson.edu/~svoboda/eta/dcWorkout/EquivCkts.html Equivalent circuits
http://jersey.uoregon.edu/vlab/Voltage/ - batteries and circuits
http://www.colorado.edu/physics/phet/simulations/cck/cck.jnlp - A
complete circuit analyzer
References
www.dannyg.com/javascript/res/resload.htm
phet.colorado.edu/new/index.php