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
 define conventional electric current, and relate
it to the direction of electron flow in a
conductor
 solve problems involving
– current
– time
– charge
Phys 12
12
Date
Class Size
Lesson #, of
17-01
 define resistance in terms of Ohm’s law
 solve problems involving
– electric potential difference
– current
– resistance
Materials:
Timeline
Class Activities
Introduction
Body
Notes 18-02, 18-03
Closure
Questions 1-5, Problems 1-11 odd
Chapter 18 Electric Currents
Static electricity was due to charges that are not in motion
• no electric field in the conductor
If there is an electric field or ∆V in the conductor then charges
move and you have electric current
18-02 Electric Current
Electrochemical cells (commonly called batteries) produce a
potential difference, which can make charges
move.
• If there is a continuous path connecting the terminals of a
battery then you have a circuit along which electrons can
flow
• circuit-construction-kit-dc_en.jar
Electric current
The net amount of charge that passes through a conductor at any
location during time t
Current is measured in Coulombs per second or Ampere
.
Current can only flow in a complete or closed circuit.
• If there is a break in the circuit it is called an open circuit
If a circuit has only one path for the current to flow then the
current is the same at all points. (simulation)
• Charge can’t appear or disappear
Example 18-1 and 18-2
In many real circuits wires are connected to a common conductor
to provide continuity.
• Ground
o Not necessarily the ground (earth)
When wires are connected to both terminals of a battery the
potential difference sets up a field in the conductor parallel to the
conductor causing electrons to flow from the negative terminal to
the positive terminal.
• Conventional current was named
before the charge of the moving
component of current was
established
o Flows from the positive
terminal to the negative
terminal
18-03 Ohm’s Law: Resistance and Resistors
The current that flows through a wire is proportional to the
potential difference applied to it’s ends
ohms-law_en.jar
Think of water flowing (I) through a pipe being pulled by gravity
(V).
• Steeper incline (more V) = more flow (more I)
The exact current also depends on the width of the pipe (resistance
of the wire R)
Ohm’s Law
Not all materials obey Ohm’s Law.
Example 18-3
All electric devices offer resistance to the flow of current.
• The wires’ resistance is usually low compared to the devices
Resistors
• Devices used to control the
amount of current
• circuit-construction-kit-dc_en.jar
See the code on page 499
Example 18-4
Electric potential decreases as current flows through a resistor
• potential drop
• voltage drop
Notes:
1. batteries do not provide constant current but (approximately)
constant potential difference
a. source of voltage
b. External to (independent of) devices in the circuit
2. Current passes through a wire or device
a. Magnitude depends on the device’s resistance
b. Resistance is a property of the device
3. Current is not a vector even though it has a direction of flow
a. The wires can turn corners without changing the
direction of the current
b. Conventional current flows from high potential (+) to
low potential (-)
c. The amount of current/charge is conserved and the
amount entering one end of a device leaves the other
end.
Questions 1-5, Problems 1-9 odd