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
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?
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