ELEC 105 Fundamentals of Electrical Engineering Spring 2010Review Topics for Exam #1The following is a list of topics that could appear in one form or another on the exam. Not all of these topics will be covered, and it is possible that an exam problem could cover a detail not specifically listed here. However, this list has been made as comprehensive as possible.Basic definitions and concepts-voltage = energy transferred per unit charge: dqdWv -voltage is “felt” in a circuit almost instantaneously after it is applied-voltage is electrical “pressure” or “force”-voltage develops across devices-current = time rate of flow of charge: dqdqi -charge on one electron = −1.602 x 10-19 C-current is electrical “fluid”-current can be relatively slow (e.g., mm/sec), but current begins to flow almost instantaneously around a circuit after a source is applied-current flows through devices-conventional current is in direction of positive charge flow, but electrons (negative charges) actually flow through wires against direction of conventional current-resistance is electrical “friction”-all materials have the property of resistivity, measured in Ω∙m (ohm-meters)-power: dtdWdtdqdqdWvip  (rate at which energy is absorbed or supplied)Basic units-voltage is measured in volts (V)-current is measured in amperes (A)-resistance is measured in ohms ()-power is measured in watts (W)-charge is measured in coulombs (C)-energy is measured in joules (J), watt-hours (Wh), or kilowatt-hours (kWh)Metric prefixes-pico (p) 1012-nano (n) 109-micro () 106-milli (m) 103-kilo (k) 10-mega (M) 10-giga (G) 10-tera (T) 10121Passive reference configuration (passive sign convention)-Ohms law: v = iR or v = −iR-power calculations: p = vi or p = −vi-sign on right-hand side depends on direction of labeled current relative to polarity of labeled voltage-if p is positive, then power is absorbed (dissipated)-if p is negative, then power is delivered (supplied)-total power delivered = total power absorbed in a circuitCircuit diagrams (symbols for batteries, resistors, wires, voltage/current sources)Voltage drops vs. voltage rises (and relationship to absorption or supply of energy)Conductors vs. insulatorsPower (watts) and energy (joules)- p = dW/dt- p = vi or p = –vi (passive reference configuration)- absorption vs. supply of power and relationship to algebraic sign of pResistance and power calculations- power is always absorbed by resistors- p = i2R- p = v2/RIdeal independent voltage source-maintains indicated voltage across its two terminals at all times-current through source is unconstrained (determined by circuit external to source)-source has no fixed resistance (i.e., no Ohm’s law calculations are possible)-batteries are practical implementations of nearly ideal voltage sources-a short circuit can be represented by a voltage source of 0 VIdeal independent current source-maintains indicated current through its branch at all times-voltage across source is unconstrained (determined by circuit external to source)-source has no fixed resistance (i.e., no Ohm’s law calculations are possible)-an open circuit can be represented by a current source of 0 ASeries and parallel connections- devices in parallel have the same voltage across them and are connected between the same two circuit nodes- devices in series have the same current flowing through them and lie along the same circuit path with no intervening junctionsCircuit node- definition: an interconnected network of conductors with no intervening devices- All points in a node have the same potential (voltage) relative to some reference point- A node can consist of several individual connection points (i.e., it is possible for a node toconsist of many branching wires)Kirchhoff’s voltage law (KVL)-simply a restatement of the law of conservation of energy in circuit terms-sum of voltage rises = sum of voltage drops-voltage rises or drops can be given either positive or negative signs in KVL equation, but must be consistent within a single KVL equation-corollary: voltage between two points = sum of voltage drops and rises between those two points-corollary: devices in parallel share the same voltage2Kirchhoff’s current law (KCL) -simply a restatement of the law of conservation of mass (charge) in circuit terms-sum of currents entering node or region = sum of currents leaving node or region-corollary: devices in series share the same currentSeries resistors-all have the same current flowing through them, but different voltages across them-NeqRRRR  21-if one resistor is orders of magnitude larger than the rest, then Req ≈ that valueParallel resistors-all have the same voltage across them, but different currents through them-NeqRRRR111121-special case for only two resistors: 2121RRRRReq-if one resistor is orders of magnitude smaller than the rest, then Req ≈ that value-equiv. resistance of any finite resistor in parallel with an infinite resistance is equal to the finite value-if two or more resistors are in parallel, majority of current flows through resistor of least valueSeries/parallel combinations of resistorsVoltage divider-formed by two or more resistors in series (all must share the same current)-% of total voltage across a resistor in a string = % of total resistance represented by that resistor-if vtot = total voltage across entire string of resistors and vk = voltage across kth resistor, thentotNkkvRRRRv21Potentiometers-wiper arm (“tap”) effectively divides the resistor into two parts and provides a connectionto the junction-voltage across “fixed” ends (terminals 1 and 3 below) usually remains constant-KVL: v13 = v12 + v23Relevant course material: HW: #1-#3Labs: #1-#3Textbook: All of Chap. 1, except material on conductanceSections 2.1-2.3, except material on current