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SAM Teachers Guide
Electric Current
Overview
Students explore the role of electron voltage and density on electric current. They
compare the movement of electrons in a conductor and an insulator. They derive Ohm’s
Law from their observations. They apply their understanding to circuits, the working of
an incandescent light, and a fuel cell.
Learning Objectives
Students will be able to:
 Explain how voltage is the driving force behind electron movement.
 Define electric current as the number of electrons flowing through a wire over a
given period of time.
 Explain how conductivity and resistivity relate to electric current.
 Infer the relationships between current, voltage, and resistance as described in
Ohm’s Law (I = V / R).
 Explain how electricity can be converted to other forms of energy.
Possible Student Pre/Misconceptions
 Electrons in a circuit come from somewhere else, rather than the circuit itself.
 Electrons travel very quickly around a wire. This explains why a light bulb turns
on as soon as someone turns on a light switch.
 Charge is used up as it flows through a circuit.
 The charge that flows through a circuit originates in the battery.
Models to Highlight and Possible Discussion Questions
After completion of Part 1 of the activity:
Models to Highlight:
 Page 2 – Voltage Model
o Link to other SAM activities: Atoms and Energy. Discuss voltage by
referring back to gravitational potential energy.
 Page 3 – Electron Density and Flow Speed
o Highlight the relationship between electron density and current of two
materials.
o Link to other SAM activities: Atomic Structure. Review the structure of an
atom, its parts, and the charges.
 Page 4 – Bottom Model of Conductivity and Resistivity
o Review the differences between conductors and insulators. Use model to
highlight the effect of temperature on current.

o Emphasize the idea that the electrons are randomly flowing in all
directions, and not in a directed flow as was modeled on page 3.
Page 5 – Ohm’s Law Models
o Use both models to highlight the relationship between current, voltage,
and resistance as shown in Ohm’s Law.
Possible Discussion Questions:
 What is the difference between current and voltage?
 What is the relationship between current and resistance?
 What is moving as an electric current flows?
 How many electrons are flowing through a typical wire? Refer to the
caption on p.3. Discuss why you might receive an electric shock.
 Do the electrons themselves flow from a power plant to your house? Why
or why not? What does get passed that distance?
 What are some real world applications that are rooted in the relationship
between temperature on insulators and conductors? [Importance in
designing space travel materials and for aircraft, satellite, and military
applications.]
 What effect does an increase in temperature have on the ability of an
insulator to insulate? On a conductor to conduct?
 Demonstration/Laboratory Ideas:
o Use a circuitry board to connect a battery and a light.
o Set up circuits and vary the wire (diameter, type of metal, etc.).
o For those who have access: CPO 13A and/or CASTLE activities.
After completion of Part 2 of the activity:
Models to Highlight:
o Page 6 – Circuit Model
o Review the flow of electrons through a circuit and how the law of
conservation of energy plays a role.
o Link to other SAM activities: Electrostatics. Review attraction /
repulsion of charges and how this plays a role in a circuit.
o Page 8 – Incandescent Light Bulb Model
o Highlight the concept of energy conversion using this model and the
role of resistance in the incandescence of the light bulb.
o Link to other SAM activities: Atoms and Energy. Review the idea of
energy transfer vs. energy conversion to a different form. This also ties
into the Law of Conservation of Energy.
Possible Discussion Questions:
 How does an incandescent light bulb work?
 What effect does adding more batteries have on the total current in a
circuit?
 How would the knowledge of hydrogen fuel cells help us in the future?
 Can you explain how the brightness of the bulbs would change if you add
or subtract parallel branches?
Connections to Other SAM Activities
The focus of this activity is to understand the motion of electric charge. This activity is
supported by Electrostatics where static charges create fields of positive and negative
charge. Electric Current shows the motion of these charged particles. Heat and
Temperature helps students explore how current can be transformed into heat and
light. Similarly, Excited States and Photons explores atoms in their excited states and
describes how they can emit photons.
The Electric Current activity supports Diffusion, Osmosis and Active Transport,
Cellular Respiration, and Harvesting light for photosynthesis. In each of these
activities, a buildup of electric potential can be converted into chemical energy if current
is allowed to flow back through the membrane. In Chemical Reactions and Energy,
electricity is one of the forms of energy that can be created if electrons in a chemical
reaction are forced through a wire.
Activity Answer Guide
2. Set the voltage to zero and observe both
Page 1:
the model and the ammeter. The electrons
are moving, but why doesn't the ammeter
measure a current?
No questions.
Page 2:
1. In the model above, describe the
relationship between voltage and kinetic
energy as the electron moves.
(a)
2. Complete the analogy: If gravitational
potential energy is the work done by gravity
on a mass moving a certain distance then
electric potential energy is...
Electric potential energy is work required to
move an electron from one position to another.
Voltage is the electric potential energy.
Page 3:
1. Does a material with a higher density of
electrons or a lower density produce a
greater current under the same voltage?
(a)
2. Copper and iron have a lot of electrons
that can flow freely. When a voltage is
applied would that produce a lot of current or
a little current? Explain.
The electrons are moving in both directions so
there is no current. Therefore there is no electric
force and the ammeter won’t measure a current.
3. How does resistance affect the current
passing through a material?
:
(b)
4. Why is the current higher in a material
with lower resistance than in a material with
higher resistance under the same voltage?
Under the same voltage the electron would feel
some electric force. Material with lower
resistance, mean that the attraction of the
electron to the atom will be lower and will result
in flow and materials with a higher resistance
would have a greater attraction and the
electrons don’t flow.
Page 6:
When a voltage is applied, a lot of current would
be generated due to the high number of
electrons that can flow freely.
1. If there were no battery describe how the
model above would change.
Page 4:
The battery supplies the energy to create the
electric potential difference. If there were no
battery, there would be no electron flow.
1. Electric conductivity measures:
(c)
2. Describe why the current measurements
are so low for an insulator.
Insulators block or slow the flow of electric
current. The electrons cannot move freely so
current measurements are low.
Page 5:
1. How does voltage affect the current
passing through a material? (a)
Page 7:
1. Imagine that the wire to the green resistor
was broken at point A. Describe what you
think would happen to the movement of the
electrons.
With the wire no longer connected at point A
electrons would no longer flow to the green
resistor. The electrons would instead only flow
through the red resistor to complete only one
branch of the circuit.
Page 8:
1. Based on your experience with the model,
explain why a light bulb from a table lamp
won't be lit if you connect it to an AA battery.
An AA battery has a voltage of 1.5 V. A light
bulb of a table lamp works under the voltage of
110 V, so the battery does not generate enough
electricity to meet the demands of the resistor
and effectively power the light bulb.
Page 9:
No questions.
Page 10:
1. Compared to conductive wires, insulators
are considered to have:
(a)
2. If two batteries were serially used in a
circuit instead of one, would the electric
current be different? Why or why not.
Two batteries in series would increase the
voltage or electric potential. Referring to Ohm’s
Law, if I = V/R, increasing the voltage would
increase the flow of current through the circuit.
This is true if the resistance is kept the same.
3. According to Ohm's Law, in any electrical
circuit, the current increases: (Choose all
that apply.)
(a) (d)
4. What causes the electric energy to change
to light energy in a light bulb?
The motion of the electrons through the resistor
increases temperature. When temperature
increases enough due to the filament’s
resistance, visible photons of light are released.
SAM HOMEWORK QUESTIONS
Electric Current
Directions: After completing the unit, answer the following questions to review.
1. Electric current can be defined as the flow of electric charges. How can you define
voltage?
2. When there is a very low density of electrons in a wire, would you expect a large current
or a small one? Why?
3. What is the difference between a conductor and an insulator? Give an example of each.
4. Ohm’s Law describes the relationship between current, voltage, and resistance. What is
the equation for Ohm’s Law? Write out the mathematical equation and then explain it in
words.
Equation:
Explanation:
5. Below is a picture of a simple parallel circuit.
a) What is represented by V? ____________________
b) Use an arrow to draw the flow of electrons through this circuit.
c) Why is I = I1 + I2? _____________________________________
6.
Explain how the presence of a resistor in a circuit can convert electricity into light? *Hint:
Think back to the model on page 8 of the activity that demonstrated incandescence.*
SAM HOMEWORK QUESTIONS
Electric Current – With Suggested Answers for Teachers
Directions: After completing the unit, answer the following questions to review.
1. Electric current can be defined as the flow of electric charges. How can you define
voltage?
Voltage is the difference in electric potential energy between two points in the path of an electron.
2. When there is a very low density of electrons in a wire, would you expect a large current
or a small one? Why?
You would expect a smaller current because there are fewer electrons flowing through a cross section of wire at
a given time.
3. What is the difference between a conductor and an insulator? Give an example of each.
A conductor allows electric current to flow through easily, such as copper. An insulator resists the flow of
electricity, such as plastic.
4. Ohm’s Law describes the relationship between current, voltage, and resistance. What is
the equation for Ohm’s Law? Write out the mathematical equation and then explain it in
words.
Equation:
I=V/R
Explanation: I = current, V = voltage, and R = resistance
Ohm’s Law states that electric current is directly proportional to
voltage and indirectly proportional to resistance.
5. Below is a picture of a simple parallel circuit.
a) What is represented by V? Voltage source such as a battery.
b) Use an arrow to draw the flow of electrons through this circuit.
c) Why is I = I1 + I2? The circuits are parallel.
6. Explain how the presence of a resistor in a circuit can convert electricity into light?
*Hint: Think back to the model on page 8 of the activity that demonstrated incandescence.
Resistance causes an increase in temperature that is high enough to cause visible photons to be emitted.