Parallel CircuitsParallel Circuits

This presentation is designed to give you a broad sense of parallel circuits

Learning Objectives- Upon Learning Objectives- Upon completion of this lesson…completion of this lesson…

Students will know what a parallel circuit looks like

Students will know the relationships of voltage, current and resistance in a parallel circuit

Students will know how to compute the missing variable given the other two in regards to a parallel circuit

DefinitionDefinition

A circuit with multiple paths from the source through the various resistors in the circuit

Parallel CircuitParallel Circuit

Parallel CircuitParallel Circuit

R=ResistanceR=Resistance

1/Rt = 1/R1 + 1/R2 + 1/R3Rt = R1 x R2 / R1 + R2Rt = R (value)/ number of resistorsThe reciprocal of the total resistance is the

sum of the reciprocals of the individual resistances

R=ResistanceR=Resistance

1/Rt = 1/R1 + 1/R2 + 1/R31/Rt = 1/8Ω + 1/12Ω + 1/24Ω 1/ Rt = .125Ω + .0833Ω + .04167Ω1/Rt = .25Ω Rt = 1/ .25ΩRt = 4 Ω

V=VoltageV=Voltage

Vt = V1 = V2 = V3V1 = 120VV2 = 120VV3 = 120VVoltage in a parallel circuit is constant

throughout the circuit

I=CurrentI=Current

It = I1 + I2 + I3I1 = V1 / RtIt = 120V / 4Ω It= 30 AmpsThe total current of a circuit is calculated

adding the total individual currentsThe total resistance is calculated using total

voltage and total resistance

I=CurrentI=Current

It = I1 + I2 + I3 I1 = V1 / R1

– 120V / 8Ω – I1 = 15 Amps

I2 = V2 / R2– 120V / 12Ω – I1 = 10 Amps

I3 = V3 / R3– 120V / 24Ω – I3 = 5 Amps

I=CurrentI=Current

It = I1 + I2 + I3I1 = 15 Amps I2 = 10 AmpsI3 = 5 AmpsIt = 15 Amps + 10 Amps + 5 AmpsIt = 30 Amps

Parallel Circuit RecapParallel Circuit Recap

Electricity takes separate paths through the resistors and back to the source

If a resistor is broken then that particular section of circuit will not work. The remaining paths will still function

Parallel Circuit RecapParallel Circuit Recap

1/Rt = 1/R1 + 1/R2 + 1/R3Rt = R1 x R2 / R1 + R2 (with only 2)Rt = R (value)/ number of resistors (when

all resistor values are the same)Vt = V1 = V2 = V3It = I1 + I2 + I3

Practice:Practice:Complete the table with a partnerComplete the table with a partner

Vt

100 V

V1 V2 V3

Rt R1

15 Ω

R2

10 Ω

R3

5 Ω

It I1 I2 I3

Practice:Practice:Complete the table with a partnerComplete the table with a partner

Vt

50 V

V1 V2

Rt R1

20 Ω

R2

10 Ω

It I1 I2

Practice:Practice:Complete the table with a partnerComplete the table with a partner

Vt V1 V2 V3

Rt R1

8 Ω

R2

8 Ω

R3

8 Ω

It

2.5 Amps

I1 I2 I3

Follow up activityFollow up activity

Be sure to check the discussion board for the follow up activity