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Basic EE Definitions, Units, Conventions, and Circuit Elements

Basic EE Definitions, Units, Conventions, and Circuit Elements. Volts, Current, Energy, Power, Sign Conventions, and Sources. Unit Prefixes. pico (p) 10 -12 nano (n) 10 -9 micro (  ) 10 -6 milli (m) 10 -3. kilo (k) 10 3 mega (M) 10 6 giga (G) 10 9 tera (T) 10 12. Basic Definitions.

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Basic EE Definitions, Units, Conventions, and Circuit Elements

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  1. Basic EE Definitions, Units, Conventions, and Circuit Elements Volts, Current, Energy, Power, Sign Conventions, and Sources Kevin D. Donohue, University of Kentucky

  2. Unit Prefixes • pico (p) 10-12 • nano (n) 10-9 • micro () 10-6 • milli (m) 10-3 • kilo (k) 103 • mega (M) 106 • giga (G) 109 • tera (T) 1012 Kevin D. Donohue, University of Kentucky

  3. Basic Definitions • Electric Circuit - an interconnection of electrical components through which charge can be moved. • Current - the rate of change of charge with respect to time (coulombs per second). • 1 Ampere = 1 coulomb per second. • 1 Volt = 1 joule per coulomb = 1 newton-meter per coulomb. • 1 Watt = 1 Ampere-Volt = 1 joule per second Kevin D. Donohue, University of Kentucky

  4. Flow Conventions I1=2 • Positive current denotes the direction of positive charge. • Describe the direction of charge in both circuits. • Indicate which elements are supplying and which are absorbing energy. B A I2=-1 B A Kevin D. Donohue, University of Kentucky

  5. Math Notation and Relationships • Current, charge, and time • Voltage, energy, and charge • Voltage, current, and power • Power supplied equals power absorbed for all elements in a circuit. Kevin D. Donohue, University of Kentucky

  6. I V I V Passive Sign Convention • It is assumed that positive charge entering the positive terminal of an element implies power absorbed by the element. • Therefore, charge leaving the positive terminal of an element implies power supplied or delivered by the element. • If the words absorbed or supplied are not given with a power value, power absorbed will be assumed. Kevin D. Donohue, University of Kentucky

  7. Example Problems • A 10 volt battery is connected to a 20 watt light bulb for 30 minutes. How much charge is lost from the battery? • 5 coulombs of charge pass from point A to point B at a constant rate. If 100 joules is absorbed, what is the voltage across AB? Kevin D. Donohue, University of Kentucky

  8. Independent Sources • Independent sources can deliver power in a circuit. An ideal source will have either a fixed voltage OR current independent of other elements in the circuit. i(t) +v(t)_ +V_ Kevin D. Donohue, University of Kentucky

  9. Power Delivered/Absorbed Examples • Find the power absorbed in each element assuming the passive sign convention a b a1) I = 2 A, V = 3 V a2) I= -1 A, V = 4 V b1) I = 6 A, V = -2 V b2) I = -2A, V = -9 V c1) I = 7 A, V = 1 V c2) I = -3A, V = -2V d1) I = 1 A, V = -1 V d2) I = -2 A, V= 6 V I +V- V I c d V I I -V+ Kevin D. Donohue, University of Kentucky

  10. 1 A - 6 V + 1 1 + 1 V- +18 V- 0.5 A 2 +- 5 V 2 Power Circuits • In a circuit power delivered must equal power absorbed over all elements. • Find power delivered and absorbed in each element. Kevin D. Donohue, University of Kentucky

  11. Dependent Sources • Dependent sources can deliver power in a circuit. The voltage or current of a dependent source depends on the current or voltage in other circuit elements. CCCS VCCS CCVS VCVS F(i1) G ( v1 ) + H ( i1 )- + E ( v1 )- Kevin D. Donohue, University of Kentucky

  12. Circuit Examples • Find power absorbed/supplied by each element in the circuit. -0.5 A + 6 V - + 1 V - 1 3 + 11 V - +5 V- 4i1 i1 0.5 A 2 Kevin D. Donohue, University of Kentucky

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