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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 electron neutron proton Atomic Structure Mass of an Electron = 9.11 x 10-28 gm. Mass of a Proton = 1.672 x 10-24 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 10-19 C 1 Coulomb = Charge on 6.242 x 1018 electrons Coulomb’s Law Like charges repel, opposites attract = k Q1 Q2 / r2 k = 9 x 109 (units?) F Coulomb’s Law Like charges repel, opposites attract = k Q1 Q2 / r2 K = 9 x 109 N m2/C2 F 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 = 6.242 x 1018 electrons/second 2 Amp = 12.484 x 1018 electrons/second In one hour - > 3600 x 12.484 x 1018 electrons Answer is 4.49 x 1022 electrons Question What’s the weight of all those electrons? 4.49 x 1022 x 9.11 x 10-28 gm 4.09 x 10-5 gm Equations I = Q/t Q=Ixt 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. Metal Conductivity (%) Silver 105 Copper 100 Gold 70.5 Aluminum 61 Tungsten 31.2 Nickel 22.1 Iron 14 Constantan 3.52 Nichrome 1.73 Calorite 1.44 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) Silver Copper 1.645 1.723 Gold Aluminum Tungsten 2.443 2.825 5.485 Nickel Iron Tantalum Nichrome Tin Oxide Carbon 7.811 12.299 15.54 99.72 250 3500 American Wire Gage (AWG) sizes AWG # Diameter (in) Ω /1000ft. 0000 0.46 0.0490 000 0.409 0.0618 0 0.325 0.0983 1 0.289 0.1240 2 0.257 0.1563 4 0.204 0.2485 10 0.102 0.9989 14 0.0640 2.525 28 0.0126 64.90 Color Coding 5 Bands of code (3 are mandatory) Bands 1 - 3 the value of the resistor Band 4 the range (tolerance) Band 5 the reliability Color Code (Band 1-3) Color Value Black 0 Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Gray 8 White 9 Example 2 6 x 103 = 26 K Ohms Band 3 (special cases) Gold = 0.1 Red Blue Gold = 2.6 Ohm Silver = 0.01 Red Blue Silver = 0.26 Ohm More Bands Band 4 Tolerance Gold 5% Silver 10% None 20% Band 5 Reliability (after 1000 Hrs of use) Brown 1% Red 0.1% Orange 0.01% Yellow 0.001% Example = 26 K Ohms ± 5%, 1 in 100,000 fails after 1000 hrs of use