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Current, Voltage and Resistance ENTC 210: Circuit Analysis I Rohit Singhal Lecturer Texas A&M University.

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Presentation on theme: "Current, Voltage and Resistance ENTC 210: Circuit Analysis I Rohit Singhal Lecturer Texas A&M University."— Presentation transcript:

1 Current, Voltage and Resistance ENTC 210: Circuit Analysis I Rohit Singhal Lecturer Texas A&M University

2 Administrative Tasks Fix Exam Schedule Lab details  TA – Mr. Pankaj Bhagawat  Sections Merge

3 Atoms and their structure

4 Atomic Structure Mass of an Electron = 9.11 x gm. Mass of a Proton = x gm. Proton is ~1836 times heavier than the electron

5 Atomic Structure Unit of Charge = Coulombs Charge on electron = charge on a proton = 1.6 x C 1 Coulomb = Charge on x electrons

6 Coulomb’s Law Like charges repel, opposites attract  F = k Q 1 Q 2 / r 2  k = 9 x 10 9 (units?)

7 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

8 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.

9 Current Rate of flow of charge 1 Amp = 1 Coulomb / 1 Second.

10 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

11 Question What’s the weight of all those electrons? 4.49 x x 9.11 x gm 4.09 x gm

12 Equations I = Q/t Q = I x t t = Q/I

13 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.

14 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.

15 Voltage Voltage is always measured between two points. It is defined as the difference of potential between the two points. Measured in volts

16 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.

17 DC Voltage Supply

18 Conductivity Copper is the most popular conductor. MetalConductivity (%) Silver105 Copper100 Gold70.5 Aluminum61 Tungsten31.2 Nickel22.1 Iron14 Constantan3.52 Nichrome1.73 Calorite1.44

19 Resistance Resistance is proportional to length length direction of current flow

20 Resistance Resistance is inversely proportional to the cross sectional area direction of current flow

21 Resistance R = ρ L/A ρ is the resistivity of the material (units?)

22 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

23 American Wire Gage (AWG) sizes AWG #Diameter (in)Ω /1000ft

24 Color Coding 5 Bands of code (3 are mandatory) Bands  the value of the resistor Band 4  the range (tolerance) Band 5  the reliability

25 Color Code (Band 1-3) ColorValue Black0 Brown1 Red2 Orange3 Yellow4 Green5 Blue6 Violet7 Gray8 White9

26 Example 26x10 3 = 26 K Ohms

27 Band 3 (special cases) Gold = 0.1  Red Blue Gold = 2.6 Ohm Silver = 0.01  Red Blue Silver = 0.26 Ohm

28 More Bands Band 4Tolerance Gold5% Silver10% None20% Band 5Reliability (after 1000 Hrs of use) Brown1% Red0.1% Orange0.01% Yellow0.001%

29 Example = 26 K Ohms ± 5%, 1 in 100,000 fails after 1000 hrs of use


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