U3e-L3 Date DRILL Why are the + and – symbols unnecessary when drawing the DC power source in an electric schematic? 1. The length of the lines tell you which is positive and which is negative

U3e-L3 Drill (cont’d) 2. What is a schematic? 3. Circle the schematic.

(1 Schematic, 1 Table, 2 formulae, 2 calculations, 2 answers) U3e-L3 Drill (cont’d) Joule’s Law & Ohm’s Law P = V I & V = I R 4. An electric fan has a power of 600 W. The voltage is 120 v AC. What is the current in this circuit? What is the resistance? (1 Schematic, 1 Table, 2 formulae, 2 calculations, 2 answers)

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Direct Current (DC) V O L T A G E Schematic TIME symbol +12 V 1 sec. 2 secs. 3 secs. 4 secs. Schematic symbol TIME

Alternating Current (AC) 1/60 SEC. V O L T A G E +120 V (1 cycle) = Voltage 0 v TIME Schematic symbol -120 V 1/60 SEC. “House current” is 60 cycles per second.

1 cycle per 1/60 sec. = ? cycles per 1 sec. FREQUENCY On the graph of “house current” (AC) voltage over time you can see that one complete cycle takes 1/60 sec. How many cycles will be completed in 1 sec.? 1 cycle per 1/60 sec. = ? cycles per 1 sec. 60 cycles per sec. The unit of measure for frequency of AC current is Hertz (Hz) 1 cycle per second = 1 Hz “House current” (from wall outlets) has a frequency of 60 cycles per second. Abbreviation is 60 Hz.

RESISTORS Resistor: A material that opposes (resists) but does not block the flow of electrons. SERIES RESISTORS If the current in a circuit must pass through 1 resistor before passing through the next resistor, the resistors are in SERIES. Series: 2 or more things of the same type following each other in succession. Schematic symbol for resistor R3 R2 R1

RESISTANCE RT = R1 + R2 + R3…… Resistance: A measure of the degree to which a material opposes (resists) electron FLOW. The total Resistance (RT) of resistors in series is the sum of their values. RT = R1 + R2 + R3……

RT = R1+ R2 + R3 RT = 1 Ω + 2 Ω + 3 Ω RT = 6 Ω R3 = 3Ω R2 = 2Ω R1 = 1Ω

Parallel Resistors If the current in a circuit passes through 2 or more resistors simultaneously, they are in parallel. R1 R2 Parallel: An arrangement that permits several tasks to be completed simultaneously rather than consecutively.

Calculate the RT for the circuit above The total resistance (Rt) of resistors in parallel is: 1 = 1 + 1 + 1 Rt R1 R2 R3 ……… R1 = 5Ω R2 = 4Ω Calculate the RT for the circuit above

1/Rt = 1/R1 + 1/R2 1/Rt = 1/5 Ω + 1/4 Ω 1/Rt = .2 Ω + .25 Ω 1/Rt = .45 Ω 1 = .45 Ω x Rt 1/.45 Ω = Rt 2.222 Ω = Rt

MIXED RESISTANCE Series Parallel

Total resistance in mixed circuits Give a letter name to any parallel segments. Solve each parallel segment. Add the RT of the parallel segments to the R of all of the resistors they are in series with. R4 = 10Ω A R3 = 5Ω R2 = 4Ω R1 = 2Ω Parallel resistors are treated as a single resistor with a single value !!!

Solve the parallel segment first 1/RA = 1/R2 + 1/R3 1/RA = 1/4Ω + 1/5Ω 1/RA = .25Ω + .2Ω 1 = .45Ω x RA 1/.45Ω = RA 2.222Ω = RA A R4 = 10Ω R3 = 5Ω R2 = 4Ω RA = 2.222Ω R1 = 2Ω Parallel resistors are treated as a single resistor with a single value !!!

Then solve for the total resistance (Rt) RT = R1+ RA + R4 RT = 2 Ω + 2.222 Ω + 10 Ω RT = 14.222 Ω R4 = 10Ω A R3 = 5Ω R2 = 4Ω RA = 2.222Ω R1 = 2Ω Parallel resistors are treated as a single resistor with a single value !!!

HOMEWORK R5=10Ω R6=8Ω What is the power of this circuit? B R6=8Ω R4=5Ω V = 12 v R2=2Ω R1=5Ω I = ? What is the power of this circuit? 1. Solve for RT 2. Solve for Current (I) 3. Solve for Power (P) HOMEWORK

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