Physics Lesson Plan
Teacher
Howard
Unit Title
Length
Goal(s)/PLO(s):
Course
Grade Level
Block/Period
K1 apply Ohm’s law and Kirchhoff’s laws to
direct current circuits
 solve problems involving
– electric potential difference
– current
– resistance
Phys 12
12
Date
Class Size
Lesson #, of
19-03
 calculate the total (equivalent) resistance for
resistors connected in parallel, series, or a
combination of both
 state Kirchhoff’s laws, and apply them to
circuits containing one source of electric
potential difference
 draw and interpret circuit diagrams
Materials:
Timeline
Class Activities
Introduction
Body
Notes 19-03
Closure
Questions 9- 12, Problems 23-33odd
19-03 Kirchhoff’s Rules
Many circuits are too complicated to analyze just using Ohm’s law
for combining series and parallel resistors. Kircchoff’s rules
summarize conservation of charge and energy in useful terms.
Kirchhoff’s First Rule (Junction Rule)
At any junction point, the sum of all currents entering the junction
must equal the sum of the currents leaving the junction.
If I 3 is entering and I 1 and I 2 are leaving then I 3 = I 1 + I 2
Kirchhoff’s Second Rule (Loop Rule)
The sum of the changes in potential energy around any closed path
of a circuit must be zero.
The gravity equivalent would be that it
doesn’t matter what path you take on a
round trip, you always end up with the
same potential energy (no change).
Using Kirchhoff’s rules
1. assign a separate current (I 1 , I 2 ,…)
for each branch of the circuit and assign a direction with
arrows
2. Identify the unknowns
a. you need a separate equation for each unknown
3. Apply the junction rule at junctions
4. Apply the loop rule around loops (one direction only)
a. for a resistor apply Ohm’s law
i. there is a decrease in potential (negative) if your
loop is the same direction as the current and vice
versa
b. for a battery
i. potential difference is positive if you went from
the negative terminal towards the positive
terminal and vice versa
5. Solve the equations for the unknowns
Example 19-8
Assign Questions 9-12, Problems 23-33 odd