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Unit 7 Parallel Circuits

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Solve the missing values in a parallel circuit using the three rules and Ohm's law. ... Unit 7 Parallel Circuits. Lights and receptacles are connected in parallel. ... – PowerPoint PPT presentation

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Title: Unit 7 Parallel Circuits


1
Unit 7 Parallel Circuits
  • Objectives
  • Discuss the characteristics of parallel circuits.
  • State the three rules for solving electrical
    values of resistance for parallel circuits.
  • Solve the missing values in a parallel circuit
    using the three rules and Ohms law.

2
Unit 7 Parallel Circuits
  • Objectives
  • Calculate current values using the current
    divider formula.

3
Unit 7 Parallel Circuits
  • Three Parallel Circuit Rules
  • The voltage drop across any branch is equal to
    the source voltage.
  • The total current is equal to the sum of the
    branch currents.
  • The total resistance is the reciprocal of the sum
    of the reciprocals of each individual branch.

4
Unit 7 Parallel Circuits
  • Parallel circuits are circuits that have more
    than one path for current to flow.
  • I (total current) 3A 2A 1A 6A

5
Unit 7 Parallel Circuits
  • Lights and receptacles are connected in parallel.
    Each light or receptacle needs 120 volts.

Panel
6
Unit 7 Parallel Circuits
  • The voltage drop across any branch of a parallel
    circuit is the same as the applied (source)
    voltage.

Panel
7
Unit 7 Parallel Circuits
  • The voltage drop across any branch of a parallel
    circuit is the same as the source voltage.

E 120 V
E3 120 V
E1 120 V
E2 120 V
8
Unit 7 Parallel Circuits
  • Parallel Resistance Formulas
  • The Reciprocal Formula
  • 1/R(total) 1/R1 1/R2 1/R3 1/R(number)
  • The Resistors of Equal Value Formula
  • R(total) R(any resistor)/N(number of resistors)
  • The Product-Over-Sum Formula
  • R(total) (R1 x R2) / (R1 R2)

9
Unit 7 Parallel Circuits
  • The Reciprocal Formula
  • The total resistance of a parallel circuit is the
    reciprocal of the sum of the reciprocals of the
    individual branches.
  • 1/R(total) 1/R1 1/R2 1/R3 1/R(number)

R(total)
R1
R2
R3
10
Unit 7 Parallel Circuits
  • Reciprocal Formula Example
  • 1/R(total) 1/R1 1/R2 1/R3 1/R(number)
  • 1/R(total) 1/50 1/150 1/300 1/100
  • R(total) 50 ohms

R(total)50 ?
R1 150 ?
R3 100 ?
R2 300 ?
11
Unit 7 Parallel Circuits
  • Resistors of Equal Value Formula
  • The total resistance of a parallel circuit is
    equal to the value of one resistor, divided by
    the number of resistors.
  • R(total) R(any resistor) / N(number of
    resistors)

R(total)
R1
R2
R3
12
Unit 7 Parallel Circuits
  • Resistors of Equal Value Example
  • R(total) R(any resistor)/N(number of resistors)
  • R(total) 24(any resistor)/3(number of
    resistors)
  • R(total) 24/3 8 ohms

R(total) 8 ?
R1 24 ?
R2 24 ?
R3 24 ?
13
Unit 7 Parallel Circuits
  • The Product-Over-Sum Formula
  • The total resistance of two resistors or branches
    is equal to the value of the product of the
    resistors divided by the sum of resistors.
  • R(total) (R1 x R2) / (R1 R2)

R(total)
R1
R2
R3
14
Unit 7 Parallel Circuits
  • Product Over Sum Formula Example
  • Step One
  • R(2 3) (R2 x R3) / (R2 R3)
  • R(2 3) (30 x 60) / (30 60) 1800 / 90
  • R(2 3) 20 ohms

R(total) 10 ?
R2 30 ?
R3 60 ?
R1 20 ?
15
Unit 7 Parallel Circuits
  • Product-Over-Sum Formula Example
  • Step Two
  • R(1 2 3) R1 x R(2 3) / R1 R(2 3)
  • R(1 2 3) (20 x 20) / (20 20) 400 / 40
    10
  • R(1 2 3) 10 ohms R(total)

R(total) 10 ?
R2 30 ?
R3 60 ?
R1 20 ?
16
Unit 7 Parallel Circuits
  • Product-Over-Sum Formula Review
  • The ohm value of two branches is combined.
  • This process is repeated using the combined ohm
    value with the next branch.
  • When all the branches are combined, this equals
    the total resistance.

17
Unit 7 Parallel Circuits
  • Current Divider Formula
  • I(unknown) I(total) x R(total)/R(unknown)

E3 120 V I3 4 A R3 30 ? P3 360 W
E 120 V I 24 A R 5 ? P 2880 W
E1 120 V I1 8 A R1 15 ? P1 960 W
E2 120 V I2 12 A R2 10 ? P2 120 W
18
Unit 7 Parallel Circuits
  • Current Divider Formula Example
  • I(unknown) I(total) x R(total)/R(unknown)
  • Find I1, I2, and I3.

E3 160 V I3 ? A R3 120 ? P3 360 W
E 160 V I 2 A R 80 ? P 320 W
E1 160 V I1 ? A R1 1200 ? P1 960 W
E2 160 V I2 ? A R2 300 ? P2 120 W
19
Unit 7 Parallel Circuits
  • Current Divider Formula Example
  • I(unknown) I(total) x R(total)/R(unknown)
  • I1 2 x (80/1200) .133 amps

E 160 V I 2 A R 80 ? P 320 W
E3 160 V I3 ? A R3 120 ? P3 360 W
E1 160 V I1 .133 A R1 1200 ? P1 960 W
E2 160 V I2 ? A R2 300 ? P2 120 W
20
Unit 7 Parallel Circuits
  • Current Divider Formula Example
  • I(unknown) I(total) x R(total)/R(unknown)
  • I2 2 x (80/300) .533 amps

E3 160 V I3 ? A R3 120 ? P3 360 W
E 160 V I 2 A R 80 ? P 320 W
E1 160 V I1 .133 A R1 1200 ? P1 960 W
E2 160 V I2 .533 A R2 300 ? P2 120 W
21
Unit 7 Parallel Circuits
  • Current Divider Formula Example
  • I(unknown) I(total) x R(total)/R(unknown)
  • I3 2 x (80/120) 1.33 amps

E3 160 V I3 1.33 A R3 120 ? P3 360 W
E 160 V I 2 A R 80 ? P 320 W
E1 160 V I1 .133 A R1 1200 ? P1 960 W
E2 160 V I2 .5 A R2 300 ? P2 120 W
22
Unit 7 Parallel Circuits
  • Review
  • Parallel circuits have more than one circuit path
    or branch.
  • The total current is equal to the sum of the
    branch currents.
  • The voltage drop across any branch is equal to
    the source voltage.
  • The total resistance is less than any branch
    resistance.

23
Unit 7 Parallel Circuits
  • Review
  • The total resistance can be found using the
    reciprocal formula.
  • The product-over-sum formula and the resistors of
    equal value formula are special formulas.
  • Circuits in homes are connected in parallel.

24
Unit 7 Parallel Circuits
  • Review
  • The total power is equal to the sum of the
    resistors power.
  • Parallel circuits are current dividers.
  • The amount of current flow through each branch of
    a parallel circuit is inversely proportional to
    its resistance.
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