Electronic BasicsDr. 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

Electrical Energy

Electrical Energy can be generated from different forms of energies

Coal, oil, natural gas Creates steam to drive a turbine that generates

electricity. Nuclear or solar energy

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 HydrogenFree 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 C1 Joule of Energy

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

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.

One C of charges/sec

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 AlternatingDirect 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

DC

AC

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 currentis 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.

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.

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/timeP = 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 = PtEnergy can also be expressed as watt-

seconds (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 = I2R

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 currentis 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.

304.2 μ

4.469

6.509

Check the numbers! Make sure you understand how we got

them!

Analyzing the circuit: Total resistance = 10+15+22+3.3=50.3KI=V/R = 0.298 mAWhat is the measurement error? About %2 error!Where does the error come from? What is the measurement error across 15K resistor?

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/dcWorkout/VandCDividers.html

http://people.clarkson.edu/~svoboda/eta/ecsa.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

phet.colorado.edu/new/index.php

www.dannyg.com/javascript/res/resload.htm