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Unformatted text preview: EE 201
Lecture 2 08/27/08 Reading and HW
• Read 1.4, 1.5, 1.6 • HW – 1.15 (due along with next lecture’s HW on coming Monday) • Mallard HW from Friday onwards • You all will be added in Mallard by today (wed) night. Try loging on Thursday and let me know if you have problems. Important stuff when solving problems Take care with units (Use SI system) Important stuff when solving problems Keep dimensional analysis check running
What is height plus ( or minus) weight ?? What is resistance plus ( or minus ) current ?? What is voltage plus (or minus) current ?? What is voltage plus (or minus) voltage ? What is voltage divided by voltage ? What is voltage divided by current ? Engineering and EE 201
• What is Engineering ? Purposeful use of science • What is EE 201 ? Purposeful (and EASY) use of Maxwell equations from physics (without knowing them !!)
Interesting, but hard stuff !! No need to know these in EE 201 or most of electronics Devices we will deal with
• Resistors • Capacitors • Inductors • Voltage sources
– Independent – Dependent
Passive devices (don’t produce electricity) • Current sources
– Independent – Dependent Active devices (produce electricity ) Voltage (V)
• • • • • • Voltage is analogous to force Newton’s first law ….. F = ma (unit = N) Ohm’s law ……………… V = RI (unit = Volts or V) Mechanical energy (Joules) = Force.distance Electrical Energy (Joules) = Voltage.charge dw V = ( w in joules, q in coulombs, V in Volts)
dq
+ V ‐ Basic circuit element • Specify VALUE, POLARITY and UNITS Current (I)
• • • • Flow of charge (rate of change of charge) dq I = (q – coloumbs, t – seconds, I – amperes) dt Current has direction Specify VALUE, DIRECTION and UNITS
i Basic circuit element Current‐charge example Power
• Power is instantaneous work (work done per unit time) dw dw dq • P = = = VI (P – watts, V – Volts, I – amps)
dt dq dt • Watch terms about power !!
– Absorbed by = consumed by = delivered to – Extracted from = delivered by = generated by Important stuff about signs
Very important points (VIP) about signs of Voltage (V), Current (I) and Power (P) • Is power consumed (absorbed) or delivered (generated) ? • Does positive power means it is consumed (absorbed) or generated (delivered) ? DEPENDS !! Depends on how you define things. Let us all define things and be consistent. PASSIVE SIGN CONVENTION !! Passive sign convention for Power Passive sign convention for Power
• After plugging in values of V and I in appropriate form for calculation of power ( p=vi…or p=‐vi as explained on previous slide)…. ….. if the resultant value of power is a positive number (+ x), that means x watts are being absorbed by the circuit element in question. ….. if the resultant value of power is a positive number (‐ x), that means x watts are being delivered by the circuit element in question Example – power and passive sign convention
+ A V ‐ I B Question: Given that V is 5 Volts and I is 5 A…..find power for A and B For A, power = ‐VI = ‐ (5)(5) = ‐25 W. Hence A is delivering 25 W For B, power = VI = (5)(5) = 25 W. Hence B is absorbing 25 W Power ‐ example ...
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This note was uploaded on 02/08/2009 for the course EE 201 taught by Professor Kruempel during the Fall '06 term at Iowa State.
 Fall '06
 Kruempel

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