Parallel Circuits Practice: Ohm's Law and Resistors in Parallel, Lecture notes of Law

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Engineering

Parallel Circuits

Practice

April 16, 2020

9-12/ Engineering Parallel Circuits Practice: [April 16, 2020]

Objective/Learning Targets:

**1. Discuss basic electricity relationships in parallel circuits

2. Build circuits from schematic drawings
3. Understand the attributes of Ohm’s law in Parallel circuits
4. Calculate Ohm’s law in Parallel circuits**

Note: You must have done lessons for April 9, 10, 13, & 14 at this point.

• Use this link and press play to enter a free simulator.
• Build this circuit, resistor values do not matter at this point.
• Click the selection in the top right for labels and values.
• You will also be calculating Ohm’s law to understand how attributes of the law apply in Parallel circuits.

Learning tools for today

Ohm’s Law

• Ohm’s Law is the mathematical relationship between current, voltage, and resistance.

Relationships of Electrical Properties

Concept Measurement Symbol (^) Formula

Voltage Volts V V Current Amperes A I Resistance Ohms Ω R

V=IR I=V/R R=V/I

• If you know two of the three quantities, you can solve for the third quantity.

• Voltage : Voltage is equal across all components in a parallel circuit.
• Current : The total circuit current is equal to the sum of the individual branch currents.
• Resistance : Individual resistances diminish to equal a smaller total resistance rather than add to make the total.

Parallel circuits Rules

• Ohm’s law in Parallel circuits
• Components in a parallel circuit share the same voltage:
  • VTotal = V 1 = V 2 =... Vn
• Total resistance in a parallel circuit is less than any of the individual resistances: Resistor Resource watts are not relevant for this activity, but still important. - RTotal = 1 / (1/R 1 + 1/R 2 +... 1/R (^) n )
• Total current in a parallel circuit is equal to the sum of the individual branch currents: - ITotal = I 1 + I 2 +... In.
• Additional Resources

Parallel Circuit Rules and Calculations

• Solve for all unknown values
• Known Values
• VT=18V
• R1=30Ω
• R2=100Ω
• R3=70Ω

2 Parallel circuit practice problem

• Solve for all unknown values
• Known Values
• VT=120V
• R1=20Ω
• R2=120Ω
• R3=40Ω

3 Parallel circuit practice problem

• Solve for all unknown values
• Known Values
• VT=24V
• R1=?Ω
• R2=?Ω
• R3=?Ω

4continued-Parallel circuit practice problem

• Solve for all unknown values and write out the band colors for each resistor.
• Use the simulator to check your work. You will need to find your own resource to check parallel resistance total.
• Known Values
• VT=48V
• R1=89Ω
• R2=47Ω
• R3=32Ω

5 Parallel circuit practice problem

branch. Because of the conservation of charge, the sum of the currents in each branchmust equal the amount going into the branch. (This is Kirchhoff's Current Law.) So, adding up the three currents, we get:

So, the total current is I = 12.0A.