Electricity Teacher Guide






Grade Level


Activity Name(s)

Current in a Simple Circuit


Voltage in a Simple Circuit

Being Prepared

In this unit, accountability pairs work well to keep one another on task and focused. Inform them up front that they need to complete "Current in a Simple Circuit" in one class period or students will get distracted and use a lot of time just trying to get the batteries on fire (yes, little picture flames show up on the screen; fortunately, this isn't a safety concern).

If you do not have enough computers for each student, pair them up and have one student run the computer for "Current in a Simple Circuit" and the other run the computer for "Voltage in a Simple Circuit". Have students discuss answers and, when they cannot agree on a response, type their names with their responses.

In using these lessons with a physics class, I would do the electrostatics with a completely separate unit.

In using these with a physical science class, I would likely pair the electrostatics lesson with a lesson on the Universal law of gravitation (or at least revisit it in discussion).

Getting Started

Big important thing: Students actually need to read the instructions, and most of the model (and probe) activities are pretty straight forward. A lot of student frustration can be avoided by making sure the students know they need to read the directions.

Current in a Simple circuit uses the Simple Circuit model. The wires need to be connected tip to tip and can be lengthened by clicking and dragging on one end. Make sure to have students show the charges/electrons so they can get the full understanding of what is going on when "electricity flows". Snapshots can be useful, especially to see if students are making unconventional connections.

Electrostatics uses several Molecular Workbench Models. Make sure students check "show atomic scale model" on the first model. For the third model, have students take at least one snapshot of a trial that did not work, at first noting it did not work, and after a successful attempt (which they should also take a snapshot of) try to explain why it did not work on the snapshot.

Voltage in a Simple circuit uses the same model as "Current in a Simple Circuit".

Suggested Timeline

The first activity, "Current in a Simple Circuit", takes around one (48 minute) class period if students are on task and focused. If you have students that struggle with reading, they may need additional time. Then, the students should do some in-class pieces with current. The second Activity, "Voltage in a Simple Circuit", even if the first activity ran a bit long, is easily doable with wrap-up in one (48 minute) class period. Some follow-up in class work would be best. The electrostatics simulation might need one and a half class periods (48 minutes) due to the third simulation where students are truly discovering how to get a specific outcome.

Thinking about the Discovery Questions

This unit is motivated by the discovery questions:

  • What is the current in parts of a simple circuit, and how do you measure it?

  • What forces do electric charges exert on each other?

  • What is the voltage across parts of a simple circuit and how do you measure it?

This unit requires students to use a simulation to make a complete circuit out of basic parts (wires, batteries, lightbulbs, resistors, and other objects that can be used to test what conducts electricity). The students then use several different circuits connecting lightbulbs or resistors in series (one path around the wires) and parallel (two or more paths around the wires). With these circuits, they investigate what current (how much charge moves in a given time) and voltage (the electric pressure) are, how they need to be measured in a circuit (current is in series; voltage is in parallel), and how these change when the lightbulbs are connected in series versus parallel. A great definition of conductor is a material which contains electric charges that can move freely. Students also explore what things exert an electrostatic force, how to change its strength, and how this force can be used to guide things (how old non-LCD TVs used to work).


Some common student misconceptions:

  • charge originates in the battery (charge is actually present everywhere in the circuit, much like water in your pipes)
  • current is how fast charge flows (rather than how much charge flows in a given time--pressure)
  • charge is used up as it moves around the circuit (the energy that pushes the charge is transferred with friction and through the light and heat released in the circuit (http://www.physicsclassroom.com/Class/circuits/u9l2e.cfm)
  • Some may think that static electricity is caused by friction (rather than the transfer or imbalance of charge), and that static means not moving (static refers to the lack of continuous movement of charge, as in a circuit)

Learning Objectives

  • NGSS
    • Performance Expectations
      • HS-PS2-4. Use mathematical representations of Newton's Law of Gravitation and Coulomb's Law to describe and predict the gravitational and electrostatic forces between objects.
      • HS-PS3-5. Develop and use a model of two objects interacting through electric or magnetic fields to illustrate the forces between objects and the changes in energy of the objects due to the interaction.
    • Disciplinary Core Ideas
      • PS2.B: Types of Interactions
        • Newton's law of universal gravitation and Coulomb's law provide the mathematical models to describe and predict the effects of gravitational and electrostatic forces between distant objects. (HS-PS2-4)
        • Forces at a distance are explained by fields (gravitational, electric, and magnetic) permeating space that can transfer energy through space. Magnets or electric currents cause magnetic fields; electric charges or changing magnetic fields cause electric fields. (HS-PS2-4),(HS-PS2-5)
    • Practices
      • Planning and Carrying Out Investigations
        • Planning and carrying out investigations to answer questions or test solutions to problems in 9-12 builds on K-8 experiences and progresses to include investigations that provide evidence for and test conceptual, mathematical, physical and empirical models.
        • Plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence, and in the design: decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of the data (e.g., number of trials, cost, risk, time), and refine the design accordingly. (HS-PS2-5)
      • Analyzing and intrepreting data
        • Analyze data using tools, technologies, and/or models (e.g., computational, mathematical) in order to make valid and reliable scientific claims or determine an optimal design solution. (HS-PS2-1)
      • Using Mathematics and Computational Thinking
        • Use mathematical representations of phenomena to describe explanations. (HS-PS2-2),(HS-PS2-4)
      • Patterns
        • Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena. (HS-PS2-4)
    • Crosscutting Concepts
      • Patterns
        • Students recognize that macroscopic patterns are related to the nature of microscopic and atomic-level structure. They identify patterns in rates of change and other numerical relationships that provide information about natural and human designed systems. They use patterns to identify cause and effect relationships, and use graphs and charts to identify patterns in data.
      • Cause and effect
        • Students classify relationships as causal or correlational, and recognize that correlation does not necessarily imply causation. They use cause and effect relationships to predict phenomena in natural or designed systems. They also understand that phenomena may have more than one cause, and some cause and effect relationships in systems can only be described using probability.
  • NSES
    • NSES Physical Science - Structure of atoms
      • Matter is made of minute particles called atoms, and atoms are composed of even smaller components. These components have measurable properties, such as mass and electrical charge. Each atom has a positively charged nucleus surrounded by negatively charged electrons. The electric force between the nucleus and electrons holds the atoms together.
      • The atom's nucleus is composed of protons and neutrons, which are much more massive than electrons. When an element has atoms that differ in the number of neutrons, these atoms are called different isotopes of the element.
    • NSES Physical Science- Interactions of energy and matter
      • In some materials, such as metals, electrons flow easily, whereas in insulating materials such as glass they can hardly flow at all. Semiconducting materials have intermediate behavior. At low temperatures some materials become superconductors and offer no resistance to the flow of electrons.

Discussion: Setting the Stage

Before the Current in a Simple Circuit, I would ask students to think about and draw whether or not they think they can make a bulb light with 1 bulb, 1 wire and a battery (and they can't cut the wire). Have them write their reasoning under their sketch. Depending on available materials and maturity, students can actually try this, though I would recommend pairs of students (it is tricky to hold the bulb against the battery to get it to light). They do not necessarily need to succeed to move to the activity; tell them they can revisit it after the Current in a simple circuit activity.

Discussion: Formative Questions

Additional discussion questions:

  • What components/elements are needed to make a complete circuit?

    A circuit needs a battery/power source and a conducting path (wire/metal). The bulb is not needed to make a circuit, but makes it useful and shows if it works.

  • What effect does changing the resistance have on current/voltage?

    Greater resistance, less current (assuming same voltage); greater resistance, greater voltage (assuming same current).

  • What is needed to have an electrostatic force?

    Unbalanced charges are necessary.

  • How can the electrostatic force be decreased?

    Decrease the amount of charge, move the objects with unbalanced charges farther apart.

  • What is happening in the wires?

    Electrons are being pushed by the battery through the wires.

  • What is electricity?

    This would be a very interesting discussion for the students that would be best to leave without a "THE ANSWER IS..." moment. See if they can at least agree on what it does (moves electrons) and what it is not.

  • Is there a relationship between voltage and current?

    The greater the voltage the greater the current given the same resistance.

  • What happens to voltage (or current) when I change the resistance of the object(s)?

    The voltage increases when the resistance increases (when the current is kept the same). The current decreases when the resistance increases (when the voltage is kept the same). See http://phet.colorado.edu/en/simulation/ohms-law for a visualization of this relationship.

Questions for students to keep in mind:

  • What is the orientation of the batteries I am connecting?

    They need to note this.

  • What effects/changes the strength of the electrostatic force?

    Increasing the size of the unbalanced charge increases the electrostatic force; decreasing the distance between the unbalanced charges increases the electrostatic forces.

  • Is there another way to arrange the components and still have the same effect (same force or current or voltage)?

    Likely yes, the point is for students to try several things and see if they can achieve this; ideally they could do a screenshot or something to show evidence of this

Discussion: Wrapping Up

  • What would happen to the current if you kept adding more elements (resistors or bulbs) in series?

    There would be no change.

  • In parallel?

    The current across each element would decrease.

  • Explain what evidence you saw to support this.

    Students' answers should include specific details, with numbers from their investigations.

  • What would happen to the voltage if you kept adding more elements (resistors or bulbs) in series?

    The voltage through each element would decrease.

  • In parallel?

    The voltage through each element would not change.

  • Explain what evidence you saw to support this.

    Students' answers should include specific details, with numbers from their investigations.

  • Explain a real life situation where static electricity is present or useful. How does this support Coulomb's law?

    Students' answers should vary; the connection to Coulomb's law should explain how when the charges are larger there is more force and/or when the charges are closer they are larger.

  • Explain Coulomb's law using an analogy or through a graphic.

    Again, students' answers should vary; the analogy to/graphic for Coulomb's law should explain how when the charges are larger there is more force and/or when the charges are closer the forces between them are larger.

Additional Background

Electrons are what is moving in a circuit. This movement is in the opposite direction of conventional current (established by Benjamin Franklin) from the positive to the negative terminal of the battery.

The term "rechargeable" battery is reinforcing student misconceptions about the battery as the source of charge. These types of batteries use a reversible chemical reaction that the application of electricity (when you "recharge" it) takes the products of the reaction and produces back the original chemicals. This "reversal" process isn't 100% efficient, so overtime the battery's ability to push charge is less as there are fewer chemicals to react (why the battery doesn't seem to "hold charge" as long).

Note: This is a simplified explanation of the chemistry involved.


Current in a Simple Circuit

  1. When two elements of a circuit are in series, what can be said about the current? Why?

    The current (flow) is the same as there is only one path for the current.

  2. When two elements of a circuit are in parallel, what can be said about the current? Why?

    The current when two elements are in parallel is a smaller value than for the element (resistor or bulb) by itself and is same for elements that are the same. The current is less through each than when the same 2 elements are in series because the flow in parallel splits between the two branches. (The same splitting would happen for more branches; 3 identical parallel branches would split the current evenly three ways.)

  3. You made a circuit with two resistors of different values in parallel. Was there more current through the resistor with a greater resistance or the one with a smaller resistance, or were they the same? Why do you think so?

    There was more current through the flow with smaller resistance because it could flow more freely.

  4. In your own words, restate the rules for combining the current across series and parallel resistors or batteries.

    Current splits when in parallel, splitting evenly if the elements in each branch are identical. Current is the same throughout a series circuit, if the elements are identical.

  5. Explain why you have to break a circuit in order to measure the current.

    The meter needs to be in series with the circuit (the circuit is broken and reconnected with the meter in series) so that they will have the same current (same flow).

  6. What is the current in parts of a simple circuit, and how do you measure it?

    Current is the amount of flow and it is measured in series with an ammeter (current meter).


  1. Particle A has a charge of +3 and particle B a charge of -3. They are 4 nm apart from each other. How would the forces change if the distance was halved? Explain your answer. Hint: Use the equation of Coulomb force for help: F=k Q1Q2/r^2 (where Q represents charge and r^2 indicates r-squared)

    If the distance is 1/2, this is squared (1/2 x 1/2 = 1/4), but this is in the denominator, so the force is 1/(1/4) or 4 times stronger.

  2. Suppose the Coulomb force is the main force responsible for most interactions between atoms and molecules. The Coulomb force gets weaker at further distance. What can you guess about the forces between molecules in a gas versus the forces between molecules in a liquid?

    Since the molecules in a gas are spread out more than when they are in a liquid, forces between molecules in a gas would be weaker than in a liquid.

  3. Suppose you shot an electron into the container pictured. The container has a particle that has a negative charge. Describe the path the electron will follow and why it follows this path.(There is an image with this.)

    The charge will be a curve down and away from the negative charge (in a parabola if students have had the math to express this) It would be beneficial for students to construct a free body (force) diagram, and discuss the forces involved to reinforce that changes in motion are a result of unbalanced forces.

  4. What forces do electric charges exert on each other?

    Like charges push away (repel), opposite charges pull together (attract). The closer together two charges are, the stronger the forces between them, regardless of if it is attractive or repulsive.

Voltage in a Simple Circuit

  1. State a rule for finding the voltage across several batteries in series.

    The voltages of several batteries in series add if they are connected + to -. (Students may also discover that if the batteries are connected - to - in series that those voltages will subtract off the total.)

  2. State a rule for the voltage across several equal-voltage batteries in parallel.

    (If the batteries are connected in parallel so that the - ends are connected to one another and the + ends are connected in parallel...) The batteries act like back-up batteries when they are in parallel (no voltage change). [If the batteries are connected in parallel with other orientations, for each battery connected with + connected with the - of another battery these will cancel voltages.]

  3. State a rule for the voltage across each of several identical resistors in series, when you know the voltage across all of them together.

    When the resistors are identical in series, the voltage splits equally across the resistors (if 3 resistors, the value splits equally 3 ways; if 4, it splits 4 ways).

  4. State a rule for the voltage across several identical resistors in parallel, when you know the voltage across all of them together.

    The voltage across each resistor is the same as any other point in the circuit. What is the voltage across parts of a simple circuit and how do you measure it? The voltage is the amount of pressure and it is measured by a voltmeter connected in parallel.

Further Investigation

Students could take their observations from the two circuit investigations and predict and do formal investigations with how changes the voltage changes the current and vice versa. An independent activity could be created in Innovative Technology in Science Inquiry to allow students to do this or they can open the activity in pHet.

Alternatively, if materials were available, students could design a circuit to contain a certain number of components without exceeding a given value for current or voltage (or both). This would be similar to considerations electrical engineers would need to address in designing outlets in a room. It is critical for student's to make sure, for either of these, as with any good experiment, that they are only changing one variable at a time. For example, if they change the current, keep the resistance the same.