Engineering (Jason Brown)

Title: Intro to Electricity

Principle(s) Investigated: Electricity, Ohm’s Law, Power Law

Standards:

• HS-PS1-1. Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
• HS-PS2-6. Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
• HS-PS3-1. Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.
• HS-PS3-3. Design, build, and refine a device that works within given constraints to convert one form of energy into another form of energy.
• 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.

Materials:

• Option A: Simulator
  • Computers, Laptops, Tablets or other internet connected devices
  • Paper
  • Writing Utensil
  • Projector/teacher computer or device (whiteboard can be used in place)
  • Phet DC Circuit Simulator (https://goo.gl/mDixOX)
• Option B: Physical Components
  • Suggested Materials (can be obtained from Amazon or local electronics stores such as Fry’s Electronics)
    • LED or Lamps
    • Batteries
    • Wire
    • Breadboard or other solderless connectors
  • Paper
  • Writing Utensil
  • Projector/teacher computer or device (whiteboard can be used in place)
• For both options it is helpful to have:
  • Presentation
  • Guided Notes

Procedure: Ask the students, how does a dimmer switch work in a house? How do electric cars regulate their speed? Show them the two diagrams of a parallel circuit and a series circuit. How can two circuits with the same components perform differently? What differences do they notice?

After a discussion of ideas, begin the lecture and explain how the items in the presentation apply to the circuits and how the circuits apply to a dimmer switch in a house and how that translates to an electric car. When explaining the components of electricity ask students where they have seen or heard these terms before. I like to apply the topic to the charging of their electronics devices and why it is important to understand basics of electricity to avoid damaging their own devices as well as application as homeowners. Explain Ohm’s Law as a mathematical relationship of electrical units and the direct connection to the dimmer switch and electric car example. If time allows, show them how to use a DVOM (digital volt ohm meter) or “multimeter” to read amperage, voltage, and resistance.

Student prior knowledge: Basic knowledge that electricity is all around us and powers many of the items we use on a daily basis.

Explanation: Setup a parallel circuit and a series circuit. It is key to understand that in a series circuit Voltage will vary and amperage will remain the same and in a parallel circuit it will be reversed. In a parallel circuit, amperage varies and voltage is constant. It can be good to equate electricity to a student’s commute home from school. More routes means less traffic (more pathways means less resistance and therefore more amperage). Explain that Resistance and Amperage have an inverse relationship; meaning as one goes up the other goes down.

Questions & Answers:

1. What does a dimmer switch do? How does Ohm’s Law Apply to a dimmer switch?
   1. A dimmer switch is simply a variable resistor (also known as a potentiometer). As the resistance does down, more amperage is allowed to flow and the light gets brighter. However, if the resistance increases then the light will get more dim as less amperage flows and eventually reaches infinite resistance allowing no amperage to pass and thus turning off the light.
2. How can you use Chemistry principles to evaluate which materials would create a better conductor or insulator?
   1. Electricity is the movement of electrons between atoms. Therefore, the fewer valence electrons (electrons in the outer shell) the easier to dislodge. Also, the more shells the atom has the less attraction there is between the valence electron and its nucleus. Therefore, the best conductor has a larger amount of shells and one valence electron.
3. Electricity is a fast and efficient source of energy and can be a clean energy depending how it is produced. If this is the case then what are the downsides to electric cars? How can we get around this?
   1. Electric cars are fast and efficient but have a limited range. Like your cell phones, if it runs down then it can take hours to recharge to the point of being useful again. One option, as we wait for battery technology to improve, is hydrogen fuel cell cars. PEM (Proton Exchange Membrane) fuel cells take oxygen from the environment and combine with hydrogen from a tank. The proton passes through the membrane and joins the oxygen to make water as the byproduct. The remaining electron is routed as electricity to power the vehicle. This is better than straight electric cars because when the power runs down you simply refuel like our current gasoline cars and are on your way again in a matter of minutes.

Applications to Everyday Life:

1. How can this apply to lightning? Why do lightning rods work? They provide a shorter and less resistant path than other surrounding items thus drawing the current towards then and away from other more harmful areas. This is also why trees get struck more often as they are taller.
2. Why does electricity start/stop people’s hearts? Our bodies ruin on electrical signals. The brain acts as a computer to send signals to work other parts of the body. Just like a computer, if you apply electricity in the wrong amounts or areas you can fry your computer, but if you apply the right amount in the right area you can power your devices.
3. How do batteries provide electricity? How does a lemon act as a power source? A typical battery is made up of a metal and an acid. In the lemon battery this is done by the natural acid in a lemon. The Zinc creates a positive ion and electrons. A conductor added between the Zinc and the copper allows the electrons to move from the Zinc to the desired circuit to power something. This is the basics of how a Sealed Lead Acid (SLA) battery operates.

Photographs: Include photos and diagrams that illustrate the how the investigation is performed.

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Guided Notes Handout

Videos: