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Understandings:
Understandings:
Circuit diagrams
Kirchhoff’s circuit laws
Applications and Skills:
Applications and Skills:
Solving problems involving potential difference, current, charge, Kirchhoff’s circuit laws, power, resistance and resistivity
Investigating combinations of resistors in parallel and series circuits
Kirchhoff's Law Scenario
Kirchhoff's Law Scenario
A junior-level electrical engineer has been given the task of creating a circuit to turn on a light bulb to two different brightnesses depending on the combination of closed switches.
A minimum of 4.0V is needed to turn on lamp. and the lamp has a maximum power rating of 3.0 W (P = IV).
What combinations of the switches will light the bulb (min 4V across the bulb)?
Switch 1 Closed - Switch 2 - Open
Switch 1 Closed - Switch 2 - Closed
Which combination will 'safely' light the bulb?
Switch 1 Closed - Switch 2 - Open
Switch 1 Closed - Switch 2 - Closed
What suggestions would you make to the junior engineer about regarding the changes he could make to improve his circuit?
Kirchhoff's Tutorials
Kirchhoff's Tutorials
Kirchhoff's Summarized
Kirchhoff's Summarized
Kirchhoff's Law #1: Current is Conserved (KCL) (Follow this link)
What goes in...must come out.
In formal terms: the total current entering a circuits junction is exactly equal to the total current leaving the same junction. Because charge is conserved through the circuit, it has no where else to go.
Kirchhoff's Law #2: Sum of Voltages is Zero (Follow this link)
What goes up... must come down.
In formal terms, for a closed loop series path the algebraic sum of all the voltages around any closed loop in a circuit is equal to zero.Within any given loop the sum of the voltages must sum to zero, as the voltage (J/C) provided by the emf source (battery) to each electron passes through the circuit it returns to the ground state (V=0).
Steps to Applying the Rules:
Steps to Applying the Rules:
Label the NODES
Assign current and direction of the current in each branch. Conventional current , flow of positive charge.
Indicate the direction you will be going around each loop when applying the voltage rule.
Apply the current rule at each junction that gives a unique equation.
Go around each loop and apply the voltage rule. Use V = I R for each resistor.
Summary from videos from above.
Resources:
Resources:
A brief, and useful, explanation of resistors in series and parallel: http://physics.bu.edu/py106/notes/Circuits.html
Systems of Equations: Geogebra
Conceptual Approach.
System of Eqn's Approach
Circuit Quantitative Reasoning
Circuit Quantitative Reasoning
Please make a copy of the Circuit Quantitative Reasoning document
Submit you solutions on the Google Classroom Assignment: Circuit Quantitative Reasoning
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