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Circuit Theory

Circuit Theory. Tashfeen Khan. Basic components and electric circuits. We will be defining the currents, voltages and powers. Be careful about the + and – signs. They may change your answers. Units and Scales. Length – m Mass – kg Current – A Voltage – V Power – W. Prefixes.

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Circuit Theory

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  1. Circuit Theory Tashfeen Khan

  2. Basic components and electric circuits • We will be defining the currents, voltages and powers. • Be careful about the + and – signs. They may change your answers.

  3. Units and Scales • Length – m • Mass – kg • Current – A • Voltage – V • Power – W

  4. Prefixes • Deci – 10^-1 • Milli – 10^-3 • Micro – 10^-6 • Nano – 10^-9 • Decka – 10^1 • Kilo – 10^3 • Mega – 10^6 • Giga – 10^9

  5. Charge • Positive charge – Proton – (+1.6*10^-19) • Negetive charge – Electron – (-1.6*10^-19) • Constant charge – Q • Instantaneous charge – q(t)

  6. Current • Transfer of charge or charge in motion • I = dq(t)/dt • Units is amperes • Current can be alternating current, direct current or exponential current.

  7. Voltage • Measure of work required to move a charge through the element. Therefore units are J/C, which is same as V. • Voltage can be alternating voltage, direct voltage or exponential voltage.

  8. Power • P = V * I (Product of voltage and current) • Follow passive sign convention • When current enters the positive terminal and leaves the negative terminal then the power absorbed is positive. • When current enters the negative terminal and leaves the positive terminal then the power supliedis positive.

  9. Independent sources • Independent sources supply voltage or current independent of any external factor. • Independent current source can be ac or dc • Is = 10 A or Is = 10cos(10t) A • Independent voltage source can be ac or dc • Vs = 10 V or Vs = 10cos(10t) V

  10. Dependent Sources • These sources depend on external variables. Following are four types of dependent sources. • Voltage controlled current source • Voltage controlled voltage source • Current controlled current source • Current controlled voltage source

  11. Ohms Law • Ohms law states that voltage across any conducting material is directly proportional to the current flowing through it. • V = I * R (where R is the constant of proportionality with units ohms)

  12. Series and Parallel Circuits • When electrical components are connected in series the current passing through them is same. • When electrical components are connected in parallel the voltage across them is same.

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