Science Milestones: Van de Graaff Generator and Tesla Coil

Last week, three local utility company employees (two of whom were linemen) spent the morning with us sharing stories and giving demonstrations about energy conservation and electrical safety.  It was a fun-filled atmosphere and everyone learned something new.

zap wow

While the lineman were giving their presentation and interacting with the kids, I was as giddy as a school girl.  I recognized the electrical “toy” on the table and was eager to play with it and allow the kids the same opportunity.   As a former teacher in a public school, I had had some experience with a Van de Graaff generator, a device that looks like a big aluminum ball mounted on a pedestal, as a source of artificial high-voltage discharges.  They are great fun in the classroom because when you touch the ball, it makes your hair stand on end as the negatively charged particles build up and push away from one another.  But as a homeschool mom, a Van de Graaff generator just isn’t in our homeschool budget.  I was in for a surprise, however, for the device was not what I thought it was – it was a higher voltage Tesla coil.

Van de Graaff Generator

To understand the Van de Graaff generator and how it works, you need to understand static electricity. Almost all of us are familiar with static electricity because we can see and feel it in the winter. On dry winter days, static electricity can build up in our bodies and cause a spark to jump from our bodies to pieces of metal or other people’s bodies. We can see, feel, and hear the sound of the spark when it jumps. You may have also done some experiments with static electricity.

A Van de Graaff generator is a device designed to create static electricity and make it available for experimentation. The American physicist Robert Jemison Van de Graaff invented the Van de Graaff generator in 1931. The device that bears his name has the ability to produce extremely high voltages — as high as 20 million volts. Van de Graaff invented the generator to supply the high energy needed for early particle accelerators. These accelerators were known as atom smashers because they accelerated sub-atomic particles to very high speeds and then “smashed” them into the target atoms. The resulting collisions created other subatomic particles and high-energy radiation such as X-rays. The ability to create these high-energy collisions is the foundation of particle and nuclear physics.

Van de Graaff generators are described as “constant current” electrostatic devices.  In the case of the Van de Graaff generator, as you approach the output terminal (sphere) with a grounded object, the voltage will decrease, but the current will remain the same. Conversely, batteries are known as “constant voltage” devices because when you put a load on them, the voltage remains the same. A good example is your car battery. A fully charged car battery will produce about 12.75 volts. If you turn on your headlights and then check your battery voltage, you will see that it remains relatively unchanged (providing your battery is healthy). At the same time, the current will vary with the load. For example, your headlights may require 10 amps, but your windshield wipers may only require 4 amps. Regardless of which one you turn on, the voltage will remain the same.

Tesla Coil

A Tesla coil is an electrical resonant transformer circuit invented by Nikola Tesla around 1891. It is used to produce high-voltage, low-current, high frequency alternating-current electricity. Tesla coils can produce higher voltages than electrostatic machines like the Van de Graaff generator described earlier.  Tesla used these coils to conduct innovative experiments in electrical lighting, phosphorescence, X-ray generation, high frequency alternating current phenomena, electrotherapy, and the transmission of electrical energy without wires.

The lineman demonstrated the coil but didn’t offer the kids a chance to try it for themselves.  When most had departed though, I approached and inquired if I couldn’t give it a go.  I was in for quite the shock!

If you are interested in exploring electricity in more depth in your homeschool, I encourage you to reach out to your local schools. It may be possible to visit a science lab at your local middle school or high school to experience a Van de Graaf generator first hand.  Many science centers also have them and even if not on public display, may be willing to organize a special class for a group of homeschoolers.  Alternatively, contact your local utility company as I did.  They may have special programs they can bring to your co-op.  You won’t know if you don’t ask.

STEM Club: Basics of Electricity

electricity

Energy is the ability to work. You need energy to force an object to move. You need energy to make matter change. The wind blowing, a river, a cormorant diving, and a falling leaf are all examples of energy in use. There are two basic types of energy, kinetic and potential. Kinetic energy is being used as an object is in motion. Potential energy is in storage just waiting to be used.

Energy is captured in many different forms.  Today, our focus is on electrical energy. Electrical energy is the movement of charged particles, negative (-) and positive (+). It can come from batteries or power plants and it can also be found in nature. Power plants burn fuel to make electricity which is then sent to homes and businesses through wires.  I thereby begin by introducing the kids to the basics of electricity – static electricity and electrical currents.

Static Electricity

Electrical charges can be negative (-) or positive (+). Opposite charges attract each other while similar charges repel each other. As electrical charges build up on a material, it creates static electricity.  A powerful example of static is the lightning bolt. Lightning is a discharge of static electricity from thunderclouds. Inside the cloud, water and ice rub together and separate positive and negative charges. The positive ice particles are lightweight and gather at the top of the cloud. The heavy negative water particles settle at the bottom until the buildup is so great the charge tries to jump to the ground where particles on the ground are positively charged. This jump emits a giant spark or lightning bolt.

Big Ideas

  • Atoms are made of extremely tiny particles called protons, neutrons, and electrons.
  • Protons and neutrons are in the center of the atom, making up the nucleus.
  • Electrons surround the nucleus.
  • Protons have a positive charge.
  • Electrons have a negative charge.
  • Neutrons have no charge.
  • Since opposite charges attract, protons and electrons attract each other.

Give it a Try

Students can see evidence of the charges of protons and electrons by doing a simple activity with static electricity.  All you need is a plastic grocery bag and a pair of scissors with which to cut the bag into strips. Give each student a strip of plastic (approx. 2-4cm x 20cm) cut from a plastic grocery bag.

  1. Hold the plastic strip firmly at one end. Then grasp the plastic strip between the thumb and fingers of your other hand.
  2. Quickly pull your top hand up so that the plastic strip runs through your fingers. Do this three or four times.
  3. Allow the strip to hang down. Then bring your other hand near it.

Expected results:  The plastic will be attracted to your hand and move toward it. Students may notice that the plastic is also attracted to their arms and sleeves.When two materials are rubbed together in a static electricity activity, one material tends to lose electrons while the other material tends to gain electron. In this activity, human skin tends to lose electrons while the plastic bag , made of polyethylene, tends to gain electrons.

Explore

  1. What happens when a rubbed plastic strip is held near a desk or chair?  (Expected results: The plastic moves toward the desk. After pulling the plastic between their fingers, the plastic gains extra electrons and a negative charge. The desk has the same number of protons as electrons and is neutral. When the plastic gets close to the desk, the negatively charged plastic repels (pushes away) electrons on the surface of the desk. This makes the surface of the desk near the plastic slightly positive. The negatively charged plastic is attracted to this positive area, so the plastic moves toward it.)
  2. What happens when two plastic strips are held near each other?  (Expected results: The strips will move away or repel each other. Since both strips have extra electrons on them, they each have extra negative charge. Since the same charges repel one another, the strips move away from each other.)

 

Electrical Circuits

In order for electricity to flow, it must follow a complete path through a circuit. A circuit starts at the source of the electricity and ends at an output device where the electricity is used or released. A switch controls the current as it flows through the circuit. For example, a circuit can start at a battery (source) and flow through a copper wire and a switch until it reaches a light bulb (output device) and back again to the battery. The electricity that flows through a circuit is current electricity. It can only flow through closed circuits, meaning there are no gaps or breaks in the path. A broken path is called an open circuit. Electrical current is measured in units called amperes. It is measured in amps.

Big Ideas

  • Electric current is energy created by the movement of electrons.
  • External energy or force must be enough to move the electrons out of orbit.
  • A closed circuit is a closed loop allowing electrical current to flow along a complete path.

Give it a Try – Exploring Circuits

Students work in small groups (2-3 students) to explore the different types of circuits – simple, series, and parallel.  Encourage them to work together to light the bulb(s).  Materials needed are:  a battery (I like to use 9 volt batteries), a minimum of four test leads or wires (I like ones with alligator clamps on each end), and at least two bulbs with sockets.

Simple Circuit

Draw a diagram of a electrical circuit that will light up just one bulb using a battery, two wires, and one light bulb.

Series Circuit

Draw a diagram of an electrical circuit that will light up two bulbs.  This time, use one battery, two bulbs, and three wires.  What happens when you unscrew one of the bulbs?     Does the brightness of the bulbs change as more bulbs are added?  

Parallel Circuit

Draw a diagram of an electrical circuit that will light up two bulbs.  Use one battery, two bulbs, and three wires. What happens when you unscrew one of the bulbs? Does the brightness of the bulbs change as more bulbs are added?

Take it Further

  • Add a switch to easily turn the lights on/off.
  • Create diagrams with appropriate symbols for the circuits we created above.

 

basics electricity

Extension Activities

  • Review or introduce the concepts discussed here with the PowerPoint Presentation shown above.
  • Have students apply their understanding of protons and electrons to explain what happens when a charged balloon is brought near pieces of paper.
  • Demonstrate how electrons can attract a stream of water.
  • Set up a series circuit with one battery, two bulbs, and three wires.  Now, remove one bulb.  In its place test a variety of materials by touching the ends of the wires to the test material. Create a list of  materials that allowed the electrons to flow through the current (conductors) and those that do not (insulators).
  • Experiment with Squishy Circuits.
  • Can you use a lemon as a battery?  Give it a try!

 

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