Presentation on theme: "Current, Voltage and Resistance ENTC 210: Circuit Analysis I Rohit Singhal Lecturer Texas A&M University."— Presentation transcript:
Current, Voltage and Resistance ENTC 210: Circuit Analysis I Rohit Singhal Lecturer Texas A&M University
Administrative Tasks Fix Exam Schedule Lab details TA – Mr. Pankaj Bhagawat Sections Merge
Atoms and their structure
Atomic Structure Mass of an Electron = 9.11 x gm. Mass of a Proton = x gm. Proton is ~1836 times heavier than the electron
Atomic Structure Unit of Charge = Coulombs Charge on electron = charge on a proton = 1.6 x C 1 Coulomb = Charge on x electrons
Coulomb’s Law Like charges repel, opposites attract F = k Q 1 Q 2 / r 2 k = 9 x 10 9 (units?)
Coulomb’s Law Like charges repel, opposites attract F = k Q 1 Q 2 / r 2 K = 9 x 10 9 N m 2 /C 2
Conduction In metals, the electrons are “more free” than the insulators. Whenever there is a charge present at one end, the electrons flow to (or away) from that charge.
Current Rate of flow of charge 1 Amp = 1 Coulomb / 1 Second.
Question If a laptop needs constantly needs 2 Amps current from a battery, how many electrons are drained from the battery in one hour? 1 Amp = x electrons/second 2 Amp = x electrons/second In one hour - > 3600 x x electrons Answer is 4.49 x electrons
Question What’s the weight of all those electrons? 4.49 x x 9.11 x gm 4.09 x gm
Equations I = Q/t Q = I x t t = Q/I
Potential Every particle of mass m raised to a height h above the earth’s surface has a potential energy m.g.h This potential energy can be raised by raising the particle a little higher When the particle is set free, it travels to the point of least potential.
Electric Potential Similarly, a charge wants to travel to a lower “electric” potential. A negative charge on the other hand, wants to travel to a higher potential. Each point in a circuit has a potential.
Voltage Voltage is always measured between two points. It is defined as the difference of potential between the two points. Measured in volts
Volts 1 volt is defined as the potential difference, which results in an energy exchange of 1 Joule due to the movement of 1 Coulomb across it.
DC Voltage Supply
Conductivity Copper is the most popular conductor. MetalConductivity (%) Silver105 Copper100 Gold70.5 Aluminum61 Tungsten31.2 Nickel22.1 Iron14 Constantan3.52 Nichrome1.73 Calorite1.44
Resistance Resistance is proportional to length length direction of current flow
Resistance Resistance is inversely proportional to the cross sectional area direction of current flow
Resistance R = ρ L/A ρ is the resistivity of the material (units?)
Material ρ (10 -8 Ohm-Metres) Silver1.645 Copper1.723 Gold2.443 Aluminum2.825 Tungsten5.485 Nickel7.811 Iron Tantalum15.54 Nichrome99.72 Tin Oxide250 Carbon3500
American Wire Gage (AWG) sizes AWG #Diameter (in)Ω /1000ft
Color Coding 5 Bands of code (3 are mandatory) Bands the value of the resistor Band 4 the range (tolerance) Band 5 the reliability