As students enter the classroom, have these questions
posted, which students should respond to:
What does static electricity have to do with electricity?
b. What basic parts of an atom contain charge? There are two—of
those two, which one has to do with electricity?
Use the garden hose to demonstrate the analogy of water
pressure with voltage, drops of water with electrons,
flow of water with electrical current, resistance of
hose and nozzle with resistance in a circuit etc. During
discussion, introduce key vocabulary terms: AMPERE,
VOLTS, OHMS, RESISTANCE, CURRENT, and CIRCUIT.
groups, have students perform the following:
Connect one, then two, and finally three 1.5 volt dry
cells in a series circuit to a socket with a 4.5 volt
bulb. The pupils will observe and explain the varying
degree of brightness of the bulb with respect to the
increased voltage and the increased current. Use the
multi-meter to measure the current for each circuit.
Connect 3 - 1.5 volt dry cells in series to both sockets,
using 4.5 volt bulbs. The pupils will notice the bulbs'
brightness as compared to using one or two dry cells.
The pupils will explain why, and then use the multi-meter
to confirm by measuring the current.
Insert the variable resistor into the circuit [You
will have to connect the negative terminal to the center
terminal with a clip], using 3 dry cells to one socket
with a 4.5 volt bulb. The pupils will vary the resistance
from the least resistance to where the bulb will not
light. The pupils will observe and explain. Again,
use the multi-meter, if available.
Through discussion, the class will realize the relationship
between current, voltage, and resistance (Noting that
this is for D.C. current only).
Introduce the pupils to
is measured in Amperes; Voltage is measured in Volts;
Resistance is measured in Ohms.
Pupils will use math skills to solve selected problems
using Ohm's Law.
Use circuit boards to set up parallel circuits with
a lamp socket on one branch, and the variable resistor
in the other branch. Introduce the term NODE.
Attach varying voltage to the circuit, while keeping
the variable resistor constant, and measure the current
through both branches using the multimeter (two multimeters
per group would be ideal). Higher voltage should result
in greater current through both branches, similar to
a series circuit. Have students collect their results
on a table similar to the following:
Now attach one 4.5 V battery to the circuit. Vary the
resistance in branch with the variable resistor in
it, and measure the currents through both branches.
Students should get the general idea that the current
will take the path of least resistance. As the variable
resistor is cranked up, the current will increase in
the other branch, making the bulb light brighter. If
the variable resistor is lowered, or even removed,
the current will want to go through that branch, so
the bulb will get dimmer. Again, students should gather
their data on a table like the following:
Finish the class with a discussion of the results that
they obtained. Attempt to lead students to the realization
that the current takes the path of least resistance.
Use the garden hose analogy to help students with this
idea. If a hose splits, and only one end has a nozzle
or stopper, it’s going to go the other way!
a. Which path did the current go through each time? Why?
b. What should you do with the variable resistor in order to make the
bulb burn the brightest? For it to be the dimmest?
c. What is the resistance of the light bulb? (Hint--when are the currents
in the two branches equal?)
The last type of circuit to analyze is a series and
parallel together. Have each group keep the circuits
the same as yesterday, but add the other resistor past
the point where the other two branches come together.
Allow the students more flexibility in examining this
circuit. Discuss first as a class what students think
will happen. Here are some questions to help their
thinking, if necessary:
a. Think about the hose analogy. What might that tell us about today’s
b. What currents might we want to measure and record?
c. Which amounts should we vary in order to test our ideas? How should
we set up a table to record data?
Monitor each group closely. Ask what hypothesis they
have regarding the circuit’s behavior. What are
they doing to test these hypotheses? Decisions on how
much to lead them might be best-made considering time
restrictions and how they’re progressing.
Depending on time, if there are groups who are struggling
to reach any conclusions, you could allow groups to
double up and share their ideas. Ask them to discuss
what their hypotheses were, how they were testing them,
and what the results were.
Discuss as a class what the students discovered. The
first principle that you should lead them to should
be Kirchoff’s Law. Kirchoff’s Law simply
states that the sum of the current coming into a node
must equal the sum of the current leaving a node. The
formula for how resistors act in parallel is a little
tricky to “discover.” However, the discussion
can get them there. Once they understand Kirchoff’s
Law, use Ohm’s law along with voltage and the
current of the entire circuit to figure out what the
equivalent resistance is. Since they know what the
resistance is of the series resistor, they can subtract
to find the equivalent resistance of the parallel portion
of the circuit. Do this as a class for a few different
data values, looking at the resistance of the bulb
(estimated yesterday), the value of the variable resistor
placed in parallel, and the equivalent resistance that
we know those two must be. The rule the students are
looking for is the following:
each student to summarize in their notes all the laws
of circuit behavior that they have learned the past
three days. Allow them the freedom to write them in
their own words, or in ways that they will remember
them. Discuss these findings as a class, or have them
fill these out as an exit card instead of their notes.
The exit card would be a good idea if you think you
need to check for misconceptions.
• Participation grade during discussions
• Homework assignments
• Exit card on the last day
• A formal lab write-up in a format that they are familiar with for your
1—Ohm’s Law problems
Day 3—Circuit problems containing Ohm’s Law and Kirchoff’s