12 Connecting resistors in parallel reduces total resistance andincreases total current.60 amp120 amp24 v24 v
13 From Chapter 2, what is Conductance and its unit Conductance (C) is:ease with which current can passthe reciprocal of resistance,Siemens
14 Parallel circuit rule for resistance The total resistance of resistors in parallel isthe reciprocal of the sum of the reciprocals of the individual resistors.For example, the resistors in a parallel circuit are 680 W, 1.5 kW, and 2.2 kW. What is the total resistance?386 W
15 The total resistance of resistors in parallel is the reciprocal of the sum of the reciprocals of the individual resistors.GT = G1 + G2 + G3 + … + GN
16 What is RT (REQuivalent) for this circuit 200350050RT = ohms
17 Special formula for calculating resistance of two parallel resistors The resistance of two parallel resistors can be found byeither:orTotal resistance of two resistors in parallel is equal the product of the two resistors divided by the total resistance.What is the total resistance if R1 = 27 kW and R2 = 56 kW?18.2 kW
18 Special formula for calculating resistance for equal resistors in parallel 500500500500500What is the value of RT100 ohms
19 Special formula for calculating resistance for equal resistors in parallel 500500500500100What is the value of RT55.56 ohms
20 Application of a parallel circuit for the exterior light system of an automobile. What happens if one headlight burns out?What happens to the current drawn by the headlight circuit?
21 Parallel circuits are used in residential wiring. WHY?
23 Voltage across parallel branches is the same. Parallel circuit rule for voltageVoltage across parallel branches is the same.
24 Parallel circuit rule for voltage Because all components are connected across the same voltage source, the voltage across each is the same.The source voltage is 5.0 V. What will a volt- meter read if it is placed across each of the resistors?
28 Application of Ohms law Calculate VS, I1, I2 and I3.Calculate IS if R3 is shorted, if R3 is open and voltage remains the sameVs = volts, RT = ohms, I1=0.023a, I2=0.009a, I3=.00505aIshort = Error; RT = 158 ohms, IS = 32mA
29 Kirchhoff’s current law (KCL) The sum of the currents into a node equals the sum of the current out of that node.
30 Kirchhoff’s current law (KCL) The algebraic sum of the currents entering and leaving a node equals zero.
38 Solving for Current in a parallel circuit when the voltage is unknown and the IT and the values of R1 and R2 are known.
39 Current dividerAssume that R1is a 2.2 kW resistor that is in parallel with R2, which is 4.7 kW. If the total current into the resistors is 8.0 mA, what is the current in each resistor?5.45 mA2.55 mANotice that the larger resistor has the smaller current.
40 Power in parallel circuits Power in each resistor can be calculated with any of the standard power formulas.Just like a series circuitPT = P1 + P2 + P3 + … + PNWhat is the total power if 10 V is applied to the parallel combination of R1 = 270 W and R2 = 150 W?1.04 W
41 What is the maximum power that the amplifier must be able to deliver? Power for one speaker = watts
42 Assume there are 8 resistive wires all with the same resistance that form a rear window defroster for an automobile.(a) If the defroster dissipates 90 W when connected to a 12.6 V source, what power is dissipated by each resistive wire?(b) What is the total resistance of the defroster?(a) Each of the 8 wires will dissipate 1/8 of the total power(b) The total resistance is1.76 W x 8 = 14.1 WWhat is the resistance of each wire?
43 When an open condition occurs in a parallel circuit: Open branches in parallel circuitsWhen an open condition occurs in a parallel circuit:the total resistance increases andthe total current decreases andthe current through all other branches (i.e. R2) remains unchanged.
44 When a lamp filament opens (or the light is turned off), the total current decreases by the amount of current in the lamp that opened. The other branch currents remain unchanged.
45 Finding an open path by current measurement. Troubleshooting parallel circuitsFinding an open path by current measurement.
46 Know how to determine if there is a open resistor Troubleshooting parallel circuitsKnow how to determine if there is a open resistor
47 Practice Exercise Complete the parameters listed in the Table. I1= R1= 0.68 kW V1= P1=I2= R2= 1.50 kW V2= P2=I3= R3= 2.20 kW V3= P3=IT= RT= 386 W VS= 5.0 V PT=7.4 mA5.0 V36.8 mW3.3 mA5.0 V16.7 mW2.3 mA5.0 V11.4 mW13.0 mA64.8 mW
48 Key TermsThe relationship in electric circuits in which two or more current paths are connected between two separate points (nodes).ParallelBranchKirchhoff’s current lawNodeCurrent dividerOne current path in a parallel circuit.A law stating the total current into a node equals the total current out of the node.A point or junction in a circuit at which two or more components are connected.A parallel circuit in which the currents divide inversely proportional to the parallel branch resistances.
49 1. The total resistance of parallel resistors is equal to a. the sum of the resistancesb. the sum of the reciprocals of the resistancesc. the sum of the conductancesd. none of the above
50 Quiz 2. The number of nodes in a parallel circuit is a. one b. two c. threed. any number
51 3. The total resistance of the parallel resistors is a kWb kWc. 5.1 kWd kW
52 4. If three equal resistors are in parallel, the total resistance is a. one third the value of one resistor.b. the same as one resistor.c. three times the value of one resistor.d. the product of the three resistors
53 Quiz 5. In any circuit the total current entering a node is a. less than the total current leaving the node.b. equal to the total current leaving the node.c. greater than the total current leaving the node.d. can be any of the above, depending on the circuit.
54 6. The current divider formula to find I1 for the special case of two resistors is b.c.d.
55 7. The total current leaving the source is a. 1.0 mAb. 1.2 mAc. 6.0 mAd. 7.2 mA
56 8. The current in R1 isa. 6.7 mAb mAc. 20 mAd mA
57 9. The voltage across R2 isa. 0 Vb Vc Vd. 4.0 V
58 10. The total power dissipated in a parallel circuit is equal to the a. power in the largest resistor.b. power in the smallest resistor.c. average of the power in all resistors.d. sum of the power in all resistors.