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**CST1511 Basic Electricity - 2**

Extra Credit Lecture Gary C. Meyer, Instructor

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**Review of Ohms Law/Power Formulas**

E = IR I = E/R R = E/I P = EI P = I2R P = E2/R

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**Series Resistors R(Total) = R1 +R2 + R3 Example: _______**

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**Series Resistors R(Total) = R1 +R2 + R3 Example: _ 30 ohms __**

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**Series Resistors + 30 V - R(Total) = R1 +R2 + R3 Example: I (Total) =**

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**Series Resistors + 30 V - R(Total) = R1 +R2 + R3 Example:**

I (Total) = E/R = 30/30 = 1 A

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**Series Resistors + 30 V - R(Total) = R1 +R2 + R3 Example:**

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**Series Resistors + 30 V - R(Total) = R1 +R2 + R3 Example:**

V (R2) = I x R = 1 x 10 = 10 v

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**Current in Series Circuit**

Use Ohm’s Law Example: R1 = 8k ohm R2 = 2k ohm I (R1) = ? E = 10 volts I(R1) =

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**Current in Series Circuit**

Use Ohm’s Law Example: R1 = 8k ohm R2 = 2k ohm I R1 = ? E = 10 volts IR1 = 10/( ) = Amps

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**Voltage in Series Circuit**

Voltage Divides Across Resistors Example: First Find Current. Next find voltages. I = R1 = 1k ohm R2 = 2k ohm V1 = I1 x R1 V2 = I2 x R2 E = 100 volts V1 = V2 =

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**Voltage in Series Circuit**

Voltage Divides Across Resistors Example: First Find Current. Next find voltages. I = 100/( ) = Amps R1 = 1k ohm R2 = 2k ohm V1 = I1 x R1 V2 = I2 x R2 E = 100 volts V1 = x 1000 = 33.3 v V2 = x 2000 = 66.6 v

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**Parallel Resistors (For Two)**

R(Total) = (R1 x R2)/(R1 + R2) Example: Rt = ? R1 = 100 R2 = 50 R (Total) =

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**Parallel Resistors (For Two)**

R(Total) = (R1 x R2)/(R1 + R2) Example: Rt = ? R1 = 100 R2 = 50 R (Total) = (100 x 50)/150 = 33.33Ω

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**Parallel Resistors (For Two)**

R(Total) = (R1 x R2)/(R1 + R2) Example: Rt = ? R1 = 2 kohms R2 = 3 kohms R (Total) = ?

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**Parallel Resistors (For Two)**

R(Total) = (R1 x R2)/(R1 + R2) Example: Rt = ? R1 = 2 kohms R2 = 3 kohms R (Total) = (2000 x 3000)/5000 = 1200 Ω

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**Current In Parallel Circuit**

Use Ohm’s Law Example: I1 = I2= E/R1 = 100/25 = 4 A E/R2 = 100/50 = 2 A R1 = 25 R2 = 50 E = 100 v It = I1 + I2 = 6 Amps

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**Power In Parallel Circuit**

Use Power Formulas Example: P1 = P2= E x I = 100 x 4 = 400 watts E x I = 100 x 2 = 200 watts R1 = 25 R2 = 50 E = 100 v Pt = P1 + P2 = 600 watts

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**Parallel Resistors 1/R(Total) = 1/R1 + 1/R2 + 1/R3**

Example: 1/Rt = 1/3 + 1/5 + 1/10 = = 0.63 Ω R1 = 3Ω R2 = 5Ω R3 = 10Ω R (Total) = 1/0.63 = 1.59 ohms

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**Parallel Resistors 1/R(Total) = 1/R1 + 1/R2 + 1/R3 Problem R1 = 2 kΩ**

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**Parallel Resistors 1/R(Total) = 1/R1 + 1/R2 + 1/R3 Problem R1 = 2 kΩ**

R (Total) = ohms

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**Parallel Resistors 1/R(Total) = 1/R1 + 1/R2 + 1/R3 Problem I = E/R**

Solve for all currents. I (R1) = I (R2) = I (R3) = I (total) = R1 = 2 kΩ R2 = 500Ω R3 = 10Ω 12 v

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**Parallel Resistors 1/R(Total) = 1/R1 + 1/R2 + 1/R3 Problem I = E/R**

Solve for all currents. I (R1) = 12/2000 = .006 A I (R2) = 12/500 = .024 A I (R3) = 12 /10 = 1.2 A I (total) = A R1 = 2 kΩ R2 = 500Ω R3 = 10Ω 12 v

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**Series/Parallel Resistors**

Use Same Principles Example: R2 = 50 R1 = 100 R4 = 60 R3 = 50 R (Total) = 100 + (50x50)/(50+50) + 60 = 185Ω

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**Currents in Combined Circuit**

Use Resistance Rules + Ohm’s Law Example: Rt = 185 ohms from a previous example. R2 = 50 R1 = 100 R4 = 60 R3 = 50 Equal resistors = Equal currents E = 370 v I (Total) = E/R = 370/185 = 2 A IR2 = ? IR3 =? IR2 = IR3 = 1 A

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**Voltages in Combined Circuit**

Use Resistance Rules + Ohm’s Law Example: Rt = 185 ohms from previous example. R2 = 50 R1 = 100 R4 = 60 R3 = 50 E = 370 v I (Total) = E/R = 370/185 = 2 A VR1 = IR1 x R1 = 2 x 100 = 200 v

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**Voltages in Combined Circuit**

Use Resistance Rules + Ohm’s Law Example: Rt = 185 ohms from previous example. R2 = 50 R1 = 100 R4 = 60 R3 = 50 E = 370 v I (Total) = E/R = 370/185 = 2 A VR2 = IR2 x R2 = 1 x 50 = 50 v

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**Voltages in Combined Circuit**

Use Resistance Rules + Ohm’s Law Example: Rt = 185 ohms from previous example. R2 = 50 R1 = 100 R4 = 60 R3 = 50 E = 370 v I (Total) = E/R = 370/185 = 2 A VR4 = IR3 x R3 = 2 x 60 = 120 v

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**Parallel Resistor Currents**

Example Problem Example: What is the current in the 20 ohm resistor? R2 =20 R1 = 100 R4 = 100 IR2 R3 = 40 It = 0.6 A IR3 IR2 = R3/(R2 + R3) x (It) = 40/60 x .6 = 0.4 A IR3 = R2/(R2 + R3) x (It) = 20/60 x .6 = 0.2 A

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**Parallel Resistor Currents**

Problem Example: What is the current in the 20 ohm resistor? R2 =10 R1 = 50 R4 = 20 IR2 R3 = 10 It = 1.0 A IR3 IR2 = R3/(R2 + R3) x (It) = IR3 = R2/(R2 + R3) x (It) =

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**Parallel/Series Resistor Voltages**

Problem Example: What is the current in the 20 ohm resistor? R2 =10 R1 = 50 R4 = 20 IR2 R3 = 10 It = 1.0 A IR3 V (R1) = V (Total) = V (R2) = V (R4) =

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**Parallel/Series Resistor Voltages**

Solution Example: What is the current in the 20 ohm resistor? R2 =10 R1 = 50 R4 = 20 IR2 R3 = 10 It = 1.0 A IR3 V (R1) = 1 x 50 = 50v V (Total) = = 75 v V (R2) = 0.5 x 10 = 5 v V (R4) = 1 x 20 = 20 v

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**Complete Worksheet 10 Basic Electricity - 2**

Optional – Extra Credit JPG File Place Worksheet in Dropbox for Worksheet 10

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