Understanding Electronic Basics: Voltage, Current, and Resistance Explained

1. Electronic Basics Dr. Farid Farahmand

2. Outline • Reviewing basic concepts: Voltage, Current, and Resistance • Ohm’s law • Power and Energy

3. 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

4. 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

5. Electrons • Electricity is due to excess of electrons! • Smallest molecule is Hydrogen • Free electrons  Electricity

6. 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.

7. 1 C 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. The potential difference is one Volt! 1 Joule of Energy

8. 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.

9. 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. Current One C of charges/sec

10. 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

11. 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

12. Applying 1 V 1 A of current is generated There must be 1 ohm of resistance! 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.

13. 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

14. 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

15. 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 watt-seconds (Ws), watt-hour (Wh).

16. 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

17. Applying 1 V 1 A of current is generated There must be 1 ohm of resistance! 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.

18. 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

19. Resistor color code

20. Ohm’s Law Given R=10 ohm; how will this graph look like?

21. Ohm’s Law

22. 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.

23. 304.2μ 4.469 6.509 Voltage and Current Measurements • 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? • 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. Check the numbers! Make sure you understand how we got them!

24. 304.2μ 4.469 6.509 Current Measurements

25. 304.2μ 4.469 6.509 Voltage Measurements

26. DO THIS PRE-LAB: • See the Web site!

27. 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

28. 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

29. References www.dannyg.com/javascript/res/resload.htm phet.colorado.edu/new/index.php