# Electricity

## DIY: Baby Plasma Cutter [W/Video]

Pencil lead and some batteries make a small plasma cutter that is used to etch a pattern in aluminum foil.
In this simple but cool demo, you are able to observe how a high velocity ionized gas (plasma) conducts electricity across a small gap between the tip of the pencil lead (graphite) and a conductive solid (aluminum foil). When electric current is applied, the carbon atoms in the graphite vaporize and ionize creating a small ball of plasma that heats and melts the aluminum foil.

Let us know if you think this demo is something you would use in your classroom. See comments below!!!

This video was produced by The Little Shop of Physics at Colorado State University in partnership with GE.

## Fun and engaging activities using the Energy Stick [W/Video]

Welcome to our March 2015 Issue of our CoolStuff Newsletter. This month, we are featuring a simple, safe and Cool device called an Energy Stick. Physics teacher James Lincoln demonstrates several experiments that help students understand the principles of electric current and light. James has authored many of our past CoolStuff Newsletters, and teachers have really enjoyed his insight, passion and creativity. We encourage you to let us know what you think, and please feel free to contribute to the conversation by submitting a comment. Thank you for being a CoolStuff subscriber – enjoy!

Arbor Scientific
We find the CoolStuff

The Energy Stick is a fun and easy way to demonstrate many of the principles of electric current and light. These topics are important for both the physics and the chemistry teacher. In this article I will outline several of these such experiments including new ones not seen anywhere else.

1) GETTING STARTED
To operate the Energy Stick, make bodily contact with both ends of it. This sends a microcurrent through your body which is amplified by the circuit inside and sent to the LEDs and speakers inside. This is how you can know whether a measurable electric current is able to flow from one side of the stick to the other.

2) CONDUCTIVITY OF VAROUS OBJECTS
One of the first experiments you will want to do with the Energy Stick is check what other objects conduct electricity. This is a good lesson in the properties of metals for chemistry, physics, or middle school science. You will find that mostly metals conduct electricity. I have also found that even distilled water conducts electricity well enough to have an effect. This should not be a surprise since the human body is mostly water and the human body works well.

Miscellaneous household items are good candidates for conductivity tests.

The open circuit fails to light

Closing hands completes the loop and current can flow

3)THE IDEA OF A COMPLETE CIRCUIT
An important lesson is that for current to flow the circuit must complete a closed loop. Thus, if there is a break anywhere in the circuit electricity cannot move through any part. This can be dramatically demonstrated by having several members of the class join hands in a ring and complete a very large circuit.

The Energy Stick’s Voltage is only about 30 milliVolts. The current output depends on the circuit it is connected through but is always only a few milliamps at most.

4) INVESTIGATIONS OF THE CURRENT
Connecting the two ends of the Energy Stick with a wire activates the circuitry inside. You can connect that wire to other electric devices such as a ammeter and voltmeter. In both cases the measurements will be quite small so it helps to have sensitive meters. The Energy Stick is a safe way to familiarize students with these probes.

5) THE PLASMA GLOBE and the Frequency of Light
A plasma globe can also be used to turn on the circuitry of the Energy Stick. Since the circuit inside amplifies very small currents, the electric field near the plasma is enough to get an effect. Inside the Energy Stick the red, green, and blue diodes turn on at different distances. This is a lesson in modern physics and chemistry. That is the meaning of the formula E=hf.

The Red Diode is the first to turn on.

As the Energy Stick is brought nearer the plasma globe, the other colors turn on. Next green, then blue last.

Red light having a lower frequency (longer wavelength) than blue and green light will can be produced at a lower voltage (energy/electric charge). Therefore, the blue diode is the last one turn on. This recalls the idea of the photoelectric effect that it is not the brightness of the light but its frequency that determines how energetic it is.

James Lincoln

Tarbut V’ Torah High School

Irvine, CA, USA

James Lincoln teaches Physics in Southern California and has won several science video contests and worked on various projects in the past few years.  James has consulted on TV’s “The Big Bang Theory” and WebTV’s “This vs. That”  and  the UCLA Physics Video Project.

Contact: [email protected]

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## Top 10 Demonstrations with the Plasma Globe [W/Video]

The plasma ball is an engaging and safe tool for studying high voltages and the electric field and can be used in middle school, high school, and college level physics courses. A very large voltage is created by a Tesla coil-like circuit and this creates a high electric field between the central electrode and the inner glass. The Field is strong enough to ionize the gases in the ball (it pulls their electrons off) and the freed electrons undergo collisions which liberate more electrons from other gas molecules. This process is known as cascade/avalanche or impact ionization. On first inspection, you will notice that the plasma ball responds to your touch. This is due to the polarization of your body (a decent conductor). As you approach the plasma ball you become polarized by the electric field and this attracts more charge to you.

1. Demonstrate plasma

Most physical science classes require that students have a cursory understanding of plasma as the “fourth state of matter.” This title is misleading because plasma is the most common state of matter in the universe and plasma was in fact the first state to exist after the big bang. Plasma is a gas-like collection of atoms that have a large number of free electric charges.  This means that newly created plasma has undergone ionization (the phase transition that is after melting and boiling). When the freed electrons are regained by ionized atoms the bonding energy is often released as visible light; therefore glowing is a signature of most plasma. Like a gas, plasma has no fixed volume and like other fluids it does not have a fixed shape.

Moving plasmas can usually be controlled by magnetic fields, but this will not be visible on the plasma of a plasma ball. In order to witness deflections of plasma, he charges must move for long enough times. A plasma ball operates on a high-frequency alternative voltage, and for this reason, the charges do not have much time to move in demonstrably measurable distances and get deflected.

Plasma is also an excellent conductor so, once one filament forms, it becomes generally stable allowing for more current to flow through it (similar to a lightning strike). This is more obvious when you bring a finger to the plasma ball. It is important to remember that plasma is very hot and it will slowly conduct heat through the glass.

2. Touch lightning

The very high voltages of the plasma ball can easily polarize a coin (or piece of aluminum foil) placed on top of the plasma ball.  By bringing your finger only a few millimeters above the penny, you will be able to elicit a spark from the top of the coin. This spark will not cause pain, or electric shock, but will be hot and if you hold your finger their long enough it might begin to hurt. The tip of the finger will now show a few harmless burn marks that will rub off in a day. Let the students touch lightning too and use this sparking technique to explain how lightning forms due to the Electric Field ionizing the air. You can also have fun burning small pieces of paper with the spark.  If you are too shy to touch the spark with your hand, you can touch a metal key (or any conductor) to the coin and the spark will still form while providing additional insulation. You should avoid touching the spark with your fingernail. Fingernails conduct electricity better than the skin and underneath it is a tissue that is dense lined with pain nerves.

3. Demonstrate convection

The plasma threads are very hot and they will rise due to their buoyancy in the other gases inside the plasma ball. For this reason, it is difficult to get a horizontal streamer to remain unbroken for more than a second – not unlike a Jacob’s Ladder. However, a vertical streamer at the top will be stabilized by the buoyancy. With practice, you should be able to get just a single vertical thread. Once again, be cautious because the glass will heat up.

4. Investigate  the oscillating electric field

The Electric Field created by the Tesla coil reaches beyond the glass dome and into the air surrounding the plasma ball. This Electric Field can easily be investigated with a small neon bulb or light emitting diode (LED). Bring either of these near the plasma ball and they will light up when aligned radially, but not circumferentially. This demonstrates that the voltages are decreasing with radial distance or (equivalently) that the Electric Field is radial. You will also notice no directional dependence of the diode because the field is oscillating rapidly.

The LED bulb (far right) is not lit at this distance

The LED bulb glows brighter as it approaches the plasma globe

The circuit is providing a high-frequency alternating voltage which is necessary to “step up” the voltage to the levels needed to operate the plasma globe. Study the voltage directly by simply connecting a probe to one of the channels on an oscilloscope and you can probe the changing voltage spatially. Some experiments include determining how rapidly the voltage decreases with radial distance or whether the voltage differences are established radially or circumferentially (the answer is the former).

For fun or if you don’t own an oscilloscope, you can also use an audio cable as a probe and listen to the frequencies on an amplifier. These will sound louder up close and quieter far away or when probed circumferentially (along an equipotential line). The human body can serve as an excellent antenna for picking up the signal so be sure to touch the tip of the cable.

One last technique is to investigate the voltage differences directly by using a digital voltmeter set to read AC. Through this investigation, one can most easily verify the distance dependence of voltage as it decreases with radial distance.

5. Illuminate a fluorescent lamp

This demonstration is normally done with a Van de Graaff generator but often results in you getting mild shocks. However, there is no pain or danger if you simply use the plasma ball!  Borrow a long fluorescent tube from your overhead lights, or buy one from the hardware store and bring it near the plasma ball. You will notice that once a part of the mercury gas in the tube gets glowing that it can stay glowing even as you extend it. There is essentially no limit to how far you can pull the tube. It also works on the household small tubes.  Emphasize that the fluorescent tube holds ionized mercury (plasma) and that plasma is a conductor (because of the free charges) and for this reason, the tube’s light can be drawn with no apparent increase in resistance (no decrease in brightness).

Also, note that the starting point of the tube must be close to the plasma ball where the Electric Field is largest (the voltage is changing the most rapidly). This can be demonstrated by moving the tube closer then further radially to the globe. At certain distances, the tube will not glow. There is a minimum Electric Field required to ionize the mercury gas and if the field is not strong enough the tube will not light.

Explain also how the fluorescent light is produced: the low pressure, ionized mercury gas releases mostly UV and violet light when it regains its electrons. This light falls on the fluorescent paint that coats the inside of the tube.  The paint then glows white. The UV light is blocked by glass, so harmful UV light does not escape the glass tubes. Thus, the process does not work in reverse: if you shine UV light on the tube from the outside the paint won’t fluoresce.

6. Create a human short-circuit

While you have the fluorescent tubes out, demonstrate that the Electric Field can be diverted to a grounded, shorter circuit if a lab-partner grabs part of the tube. This will reinforce the idea of lightning and currents (perhaps later on) taking the path of least resistance. It will also awaken students to the reality that their bodies are paths through which electricity can flow. (A valuable lesson in electrical safety!)

Fluorescent tube lights at point of contact continues with no obstruction

Touching the fluorescent tube diverts the current

7. Analyze the spectrum of the gases within globe

When it comes to analyzing the spectrum of the gases in your plasma ball, a good place to start is to analyze the point where your finger touches. Looking straight at the plasma globe, place a finger as far to one side as possible. This should create what looks like a vertical (pink?) stripe. Analyze this with your diffraction grating and compare the spectrum to known inert (noble) gases. Since there is often more than one gas, this can be difficult but is worth the effort.

To analyze the (bluish white) streamer filaments, it is helpful to create the vertical streamer from experiment #3. This vertical column will be ideal for analyzing its spectrum. It is best to have a partner supply a free hand and beware once again of the plasma heating up the glass. This may also be a good time to break out the digital spectrometer or other spectrum-analyzing equipment to get specific wavelengths measured. Different plasma globes use different gases and in different amounts, but they are almost always noble gases.

8. Hold ionized gases in the palm of your hand

Neon gas tube near plasma globe

Ionizing gases and observing their spectra is normally associated with dangerous, high-voltage equipment that only instructors can handle. But now you can put ionized neon tubes in the hands of eager students because your plasma ball ionizes them safely. No longer is a black box needed to confuse students as to what is happening. The plasma ball’s strong Electric Field rips the electrons off their atoms and unique colors are produced as electrons are reacquired by the various orbitals. Teaching about the emission spectrum of ionized gases can now become a hands-on activity.

9. Power up your cathode ray tube

A plasma ball provides a safe source of high-voltage that can allow you to investigate the properties of cathode rays safely. A typical concern with doing cathode ray tube experiments is that you have to connect your CRT to a dangerous high-voltage source. Teacher and student alike can now safely and easily demonstrate the magnetic deflection of electrons and relive the discoveries of J.J. Thomson thanks to their marvelous plasma globe.

10. Demonstrate an absorption spectrum

A plasma globe provides a rare chance for you to demonstrate that light is absorbed by ionized gases.  Send a beam of collimated, white light into the plasma housing and you will be able to observe the absorption spectrum. Collimated light is produced by sending a bright beam through two holes on either side of a box; this guarantees that the light that emerges is a narrow column. Note that projectors that mix RGB will not suffice as a white light source – the light has to be a full rainbow.  The best source is a bright incandescent flashlight or an overhead projector.  Focus the beam so it passes through the plasma, then separate it with a diffraction grating or prism and project the rainbow on a screen or wall.  When the plasma globe is off, the white light will split into a full rainbow.  When the globe is on, some of the colors will be missing as thin bands. Most notably will be the yellow and reds observed in the emission spectrum from earlier. This will verify that emission and absorption spectra have the same wavelengths.

conclusion:

In conclusion, the plasma globe is an under-utilized and relatively familiar piece of lab equipment. I strongly recommend that every physics teacher include one in his or her laboratory and use them to make electrostatics as hands-on as possible.

James Lincoln

Tarbut V’ Torah High School
Irvine, CA, USA

James Lincoln teaches Physics in Southern California and has won several science video contests and worked on various projects in the past few years.  James has consulted on TV’s “The Big Bang Theory” and WebTV’s “This vs. That”  and the UCLA Physics Video Project.

Contact: [email protected]

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## Tesla’s Million Volt Revenge [W/Video]

On October 8th, 2012, magician David Blaine performed a seemingly life-threatening stunt subjecting himself to a whopping one million volts of electricity while wearing a 20-pound chain metal suit.

The public was shocked by the performance, a demonstration that seems to defy the basic laws of science. However, an understanding of the laws of electricity will show that Blaine was not working against these basic principles, but was using them in order to perform his trick successfully!

In the video of Blaine’s performance shown above, the magician is wearing a Faraday Cage – a type of suit made of a conductive material invented in 1836 by English scientist, Michael Faraday. The suit functions as a shield that blocks external static and non-static electric fields which causes the electric charges within the Cage’s conductive material to redistribute themselves and thus cancel the field’s effects in the cage interior. This same phenomenon explains why one is safe from lightning storms and other external electric fields while driving a car (not the rubber tires, despite what Grandma may have told you!)

So while Blaine’s performance looks pretty dangerous, his Faraday Cage (which, theoretically, has no voltage limit) prevents the electric current from reaching his body, making it not quite the superhuman feat it appears. Nevertheless, showing this video to your physics classes will have even the bravest students on the edge of their seats – until you explain the principles behind it!

Other common uses for a Faraday cage include:

• Your microwave oven & its door preventing the Radio Frequencies/Energy within the oven from leaking out.
• Elevators simulate a Faraday cage effect, leading to a loss of signal and “dead zones” for users of cellular phones & radios which require electromagnetic external signals.
• The shielding inside of coaxial television cable wire & USB cables protect the internal conductors from external electrical noise and prevents the RF signals from leaking out.
• Plastic bags impregnated with metal are included with highway electronic toll collection devices which are to allow motorists to place them in the bag so that a toll charge is not registered or a device will not register a charge while being shipped to a customer’s home after ordering in a delivery truck.
• Even MRI machine scan rooms are designed as Faraday cages to prevent external radio frequency signals from being added to data collected from the patient, which would affect the resulting image.
• Shopping bags lined with aluminum foil have even been found by police in arresting shoplifters who steal RF-tagged items; the bags acting as Faraday cages.

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## Recreate Physics History: Build a Voltaic Pile

In the late 1700s, Italian scientist Luigi Galvani stumbled across one of the most important discoveries of all time. He found that frog legs would contract when some of the muscles and nerves were connected – even when the frog was dead! Galvani attributed this phenomenon to the idea that animal and human brains produce electricity, which he referred to as “animal electricity.” He surmised that this electricity was then stored in the animal’s muscles after being transported to the muscles through the nerves, much like how electricity is stored in a Leyden jar. According to Galvani, when certain muscles and nerves were connected, animal electricity discharged and the muscles contracted.

Can’t view this in YouTube? Try watching in Vimeo.

Italian scientist, Allesandro Volta, read about Galvani’s work and through experimentation came to strongly disagree with Galvani’s explanation of the phenomena, especially the idea that living beings produced “animal electricity.” Volta instead believed that the electricity present in the frog was the result of the contact of the metal probes with the frog tissue. In 1791, Volta produced continuous electric current when he placed a cloth soaked in salt water between silver and zinc disks. In 1800, Volta discovered that the current increased when he stacked several pairs of these single electrochemical cells together. This device became known as the voltaic pile, and was the first electrochemical battery. You can learn more about the debate between Volta and Galvani and its significance to the fields of both electricity and anatomy by viewing the video below:

You can make your own voltaic pile out of simple and inexpensive materials. Although Volta used silver and zinc, it is more feasible – and inexpensive – to use copper and zinc for the metal disks. Even though pennies are no longer made of copper, their copper coating still makes them a great choice for copper disks, and zinc disks can be obtained by purchasing galvanized electrical boxes and punching out the holes. The electrical box seen on this page and in the video was purchased at a local home improvement store for only \$0.74 and provides 17 zinc disks. Other materials needed include thick card stock, salt water, a voltmeter or multimeter, and scissors. Wooden dowel rods poked into modeling clay can provide vertical support for the pile as more and more cells are stacked on top of each other, and more closely replicates the design of the original Voltaic pile. You may also want to include an LED and connecting wires as your voltaic pile should generate enough power to light an LED.

Voltaic Pile Materials

To make the voltaic pile, cut out card stock disks the size of a penny and soak them in a cup of salt water. To make a single cell, place a card stock disk that was soaked in salt water on top of a zinc disk, and then place a penny on top of the card stock. Touch the positive probe of a voltmeter to the copper and the negative probe to the zinc and you will find that the electric potential difference, or voltage, of this simple electrochemical cell will likely be between 0.60 V and 0.80 V. If you make another cell and stack, or pile, it on top of the other so that you essentially have two cells in series, you should find that the resulting electric potential difference is between 1.20 V and 1.60 V. If you continue to pile single cells made of a zinc-card stock-copper sandwich on top of each other, you will find that the voltage increases with each additional cell. Small wooden dowel rods poked into modeling clay can be used to keep the stack of electrochemical cells from falling over. The voltaic pile illustrated below was made of multiple zinc-card stock-copper cells and had an electric potential difference of 3.26 V at the time of the photo, although it had initially read larger. Unfortunately, you can expect to have fluctuations and inconsistencies in voltage readings, but readings should generally increase as additional cells are added.

Voltaic Pile with Multiple Cells

You should be able to connect an LED to your voltaic pile and watch it light. LEDs are directional, which means that the positive lead (the longer of the two leads exiting the bottom of the bulb) must be connected to the positive (copper) terminal of your voltaic pile.

LED Lit by Voltaic Pile

The Voltaic Pile

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## The Electricity & Magnetism Light Bulb Demo Will Light Up Minds

The link between electricity and magnetism finds its legendary roots back to Hans Christian Orsted when he supposedly found that electric current affected his compasses during a student lecture.  That piece of scientific history may be one of exaggerated legend, but the marriage of electricity with magnetism has been widely known for over a century, later to be given a full mathematical explanation by Lord Kelvin and James Clerk Maxwell.  The concept of electron movement causing the production of an ensuing magnetic field is a fundamental model used in describing electromagnets, generators, transformers and electric motors.

Can’t view this in YouTube? Try watching in Vimeo.

Students can witness the magnetic fields produced by electron movement using compass deflections and observe first-hand the mechanical spin of a solenoid in an electric motor.  Using the “Electricity & Magnetism Light Bulb Demo”, you will demonstrate to your students the relationship between electricity and magnetism in an amazing and unconventional way, using a Victorian light bulb under conditions not normally observed in everyday life. When a wire that carries an electrical current is placed within a magnetic field, each of the moving charges, which comprise the current, experience the Lorentz force and together they can create a macroscopic force on the wire.  The following equation, in the case of a straight, stationary wire is as follows:

…where is a vector whose magnitude is the length of wire, conventional current flow I, B is the Magnetic Flux Density and F is the force on the wire.

### The Electricity & Magnetism Light Bulb Demo can clarify several important concepts:

1.   Using DC (Direct Current), electrons flow through a bulb’s filament in one direction.

2.   Using AC (Alternating Current), electrons flow through a bulb’s filament in two directions.

3.   A magnetic field is produced when electrons flow through a conductor.

4.   When magnets are placed near wires that carry electric current, a force is exerted on the wire. (Technically, the force is on the electrons in the wire.  The electrons are “trapped” in the wire therefore causing the wire to move instead of the individual electrons.)

5.   When a wire carrying an electrical current is placed in a magnetic field, each of the moving charges (electrons), which comprise the current, experiences the Lorentz force and together they can create a macroscopic force on the wire itself.

### Acknowledgements:

Thank you to Buzz Putnam, Physics Teacher and Whitesboro High School Science Department Chairman, for his development of this product and his assistance in writing these instructions.

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/td>
Hand made Victorian light bulb, replica of Thomas Edison’s original design, 60W, carbon filament.

### Demonstrate Magnetic Fields, Electric Current, and Basic Principles of the Motor.

In 1820, Danish physicist/chemist Hans Christian Ørsted (Oersted) noticed that when current from his Voltaic pile was switched on and off, a compass needle placed near the wire deflected from true magnetic north. Within a few months of careful study, he deduced that a magnetic field circles a current-bearing wire.

It was not long before scientists and inventors found practical applications of this discovery. In 1821, English physicist/chemist Michael Faraday made brilliant use of two fundamental principles: 1) magnetic fields circle current-bearing wire, and 2) magnetic fields interact with other magnetic fields. He found that the magnetic fields around a permanent magnet and a current-bearing wire could be made to interact and cause motion. This was essentially the first electric motor, and modern motors still operate on this same principle.

Faraday used wire, a battery, a permanent magnet, and a dish of mercury to make his first motor. When current flowed through his circuit, the magnetic field induced around the wire that hung free in the mercury interacted with the magnetic field around a permanent magnet placed within the mercury. This interaction caused the free wire to rotate around the permanent magnetic whenever current flowed through the circuit. You can view a simulation of this early motor at magnet.fsu.edu.

It is fairly simple to construct a working motor similar to Faraday’s original motor that will amaze your students. Due to safety concerns, salt water is substituted for mercury.

Materials: plastic 2L bottles, connecting wires, modern Voltaic pile (i.e., 9V battery), neodymium magnets, salt water, tape, modeling clay, stiff copper wire, aluminum foil, 2 small paper clips, plastic straw, switch (optional)

Construction: Cut one 2L bottle approximately 4 in tall. Place some modeling clay in the bottom of the bottle. Place a stack of neodymium magnets in the tub. Standard steel bar magnets are likely not strong enough. Fill with salt water. Tape the straw to the top of the second 2L bottle. Place stiff copper wire through the straw and attach the paper clips to a hook bent on the end of the wire. The paper clips will serve as a swivel and allow free movement of the hanging stiff cooper wire around the stack of magnets. Connect the other end of the top wire to one terminal of the 9V battery. Connect the other terminal of the 9V battery to the switch. Connect the switch to a folded over piece of aluminum foil. Place the other end of the aluminum foil in the salt water. Connect the other stiff copper wire to the swivel so that it rests in the salt water near the magnet stack. Close the switch and observe the copper wire. Reverse the battery terminals and notice any change in the motion. Turn the stack of magnets over and notice any change in the motion.

Note: Thank you to Dr. Joel Bryan of Ball State University in Muncie, IN for authoring this article and video.

Listed below are the items we sell that will help you construct your motor. In addition to these items you will need 2 plastic 2L bottles, salt water, tape, aluminum foil, 2 small paper clips, and a plastic straw.

## Homopolar Motor Kit

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## High Voltage and High Drama: Right in Your Classroom!

Using high voltage equipment in the classroom can be exciting and educational for students, but most students AND teachers do not realize the real-life applications of such devices in their everyday lives. Although high voltage components are used in many of today’s electronic gadgets, being able to demonstrate the principles of this electrical phenomenon can be confusing for students and may present a safety issue for the teacher if not properly used. A Leyden Jar, Wimshurst Machine and Tesla Coil demonstrate the basic fundamentals of electricity while showcasing these historically-rich devices that most students have never seen. At the most basic level, the electrical forces between electrons and protons drive the underlying concepts behind these devices, whether it is the storage of electrical charge in a Leyden Jar or the Electrical Potential Energy produced by a Tesla Coil. All of these electrical phenomena are governed by the same three basic principles;

1. Electrons are the “bits” of the atom that can be removed or added.

2. Electrons are repelled by other electrons and attracted by the protons. Or, in a simpler way… Two negatively-charged particles repel and two positively-charged particles repel while a positively-charged and negatively-charged particle attract.

3. Electrons tend to move from a greater negative concentration to a “place” where there is a lower negative concentration.

The following collection of demonstrations utilizing a Leyden Jar, Wimshurst Machine and a Tesla Coil, are designed to “spark” student interest in learning about basic concepts of electricity.

Part 1 – The Leyden Jar

Ever heard of a Leyden Jar? It’s been around for over 200 years and is the forerunner of the modern day capacitor. The Leyden Jar is a device that “stores” static electricity between two electrodes on the inside and outside of a container. The gentleman who invented it tested it on himself and stated that “my whole body was shaken as though by a thunderbolt.” It was invented by Pieter van Musschenbroek in 1745 in Leiden, Netherlands, which gave the invention its name. It is essentially an early form of a capacitor. In the early years of electricity research, scientists had to resort to large insulated conductors to store charge so the Leyden Jar provided a much more compact alternative and they were able to store substantial charge receiving a significant shock from the device when discharged. A large Leyden Jar was once discharged through seven hundred monks who were holding hands. They flew up into the air simultaneously!

The original form of the device was just a glass bottle partially filled with water, with a metal wire passing through a cork closing it. Scientists believed that a form of liquid would be the most suitable for storage of charge. A few years later, however, researchers had learned that water was not necessary, but a metal hull inside and outside the jar was sufficient for storing electrostatic energy. Lining the interior and exterior of the glass jar with conducting metal foil proved to be the most efficient and effective way of storing charge. The foil is lined to the mouth of the jar, preventing the charge from arcing between the foils. A rod electrode projects through the mouth of the jar, electrically connected by some means (usually a chain) to the inner foil, to allow it to be charged. The jar can be charged by any source of electric charge, connected to the inner electrode while the outer foil is grounded. The inner and outer surfaces of the jar store equal but opposite charges. When the brass rod is connected to a source of electricity, current travels through the rod and charges the inner foil. Current cannot pass through the glass, but the foil on the outside becomes charged by induction if it is properly grounded. The outer foil has a charge opposite to the charge inside the jar. When the flow of current into the jar stops, a charge remains stored in the jar. If the inner layers of foil and outer layers of foil are then connected by a conductor, their opposite charges will cause a spark that discharges the jar. Early experimenters found that the thinner the dielectric (insulated cup), the closer the plates, and the greater the surface, the greater the amount of charge that could be stored at a given voltage.

Experimenting with large Leyden Jars improperly can be very dangerous. In 1783, while trying to charge a battery during a thunderstorm, Prof. Richmann was killed by accidentally getting too close to a jar with his head. He is the first known victim of high voltage experiments in the history of physics. Benjamin Franklin was lucky not to win this honor when he performed his kite experiments. Franklin had later investigated the Leyden Jar and concluded that the charge was stored in the glass, not in the water, as others had assumed.

1. The dissectible Leyden Jar can be charged by a student using a plastic rod and animal fur (…a PVC pipe or plastic golf tube works quite well) rubbed together and touching the top electrode several times. After charging, the jar can be discharged with a conductor on an insulated handle by shorting the inner and outer can to show charge storage.

2. Charging the Leyden Jar again, the teacher is able to lift out the inner can with an insulated tool or with care, by hand. At this point the parts of the jar are safe to handle, and the plastic cup jar can be lifted out, the inner and outer cans touched to each other, or touched to the glass jar in any combination. You can even give the pieces to the students to handle. When the Leyden jar is reassembled, the last step of inserting the inner can must be done carefully. The students will find that the jar is still charged and can be checked by shorting its terminals and drawing a spark! The amount of capacitance (The ability of a body to hold an electrical charge) for a Leyden Jar (Capacitor) was originally based on the measured number of ‘jars’ you had lined up of a given size, assuming reasonably standard thickness and composition of the glass. A typical Leyden Jar of one pint size has a capacitance of about 1 nF (NanoFarad).

3. You can make your own Leyden Jar!

a. Using an empty film canister, place the lid on the film canister and push a nail (…a large dissecting pin works well!) down through the center of the lid.

b. Wrap the bottom 2/3 of the file can with aluminum foil. Taping it won’t hurt anything.

c. Fill the film can with water. Make sure that it’s full enough so that the nail touches the water. Now you can charge it…

d. Using a plastic rod and animal fur, rub the plastic rod with the animal fur and hold the Leyden Jar by the aluminum foil.

e. Charge the jar by touching the charged plastic rod to the nail stuck through the lid of the Leyden Jar and add more charge to the Leyden Jar over and over again.

f. Now discharge the jar by touching the aluminum foil with one finger AND the protruding nail with the other finger and you will “feel” a jolt!

The Wimshurst Machine is an electrostatic device for generating high voltages developed around 1880 by British inventor James Wimshurst. It consists of two large oppositely-rotating discs mounted vertically, two cross bars with metallic brushes, two Leyden Jars for charge storage and a spark gap formed by two metal spheres. This machine separates electric charges through electrostatic induction. In a Wimshurst Machine, the two insulated disks are turned mechanically. Their metal plates rotate in opposite directions with two pairs of copper brushes removing charges from the plates. These are collected by metal combs with points placed near the surfaces of each disk and causing an imbalance of charges to be stored and amplified in the two Leyden Jars. When the charge difference becomes too great, a spark will jump across the gap, depending on the gap distance, plate sizes, Leyden Jar sizes and the humidity of the room. A typical Wimshurst Machine can produce sparks that are about a third of the disk’s diameter in length and several tens of microamperes. The Wimshurst Machine from Arbor Scientific is rated at 7µA. The maximum Electrical Potential Difference is approximately 75,000V.

The Wimshurst Machine works best on a dry day, with the disks very clean and turning the crank rapidly charging the disks and Leyden Jars to a very high voltage. In humid weather, a hair dryer can be used to dry the machine and make it work.

a. Basic spark discharge. Separate the ball terminals by a small distance. Turn the crank to create opposite charges in the terminals. When the voltage difference between the terminals is sufficient, a spark will form. (The maximum spark distance will vary depending on the humidity.

b. Effect of Leyden Jars. Using the thumbscrews, remove the metal bar at the base of the apparatus to disconnect the Leyden Jars. Observe the change in the size and frequency of the sparks when the charge is delivered only to the terminals.

c. Hold a small circuit board by the insulated area and connect the Wimshurst to the circuit. By cranking the machine, a complete circuit can be shown “flashing” at each discharge of the machine.

d. Using a plastic protractor or some other thick piece of plastic, hold the plastic between the terminals and the “spark” will jump around the plastic (insulator). Do it in the dark for maximum viewing!

e. Volta’s Hail Storm. Separate the ball terminals by a large distance. Connect one to the top terminal of the Volta’s Hail Storm apparatus (P6-3320), and the other to the bottom. Turn the crank and observe the behavior of the “hail” in the apparatus as it is alternately attracted to and repelled from the plates.

f. Franklin’s Bells. After explaining the behavior of “Volta’s hail storm”,

build a Franklin’s Bell set-up. You need two empty soda cans, a wooden dowel, a large insulated platform to set the cans on (Styrofoam works well) and a string tied to the pop-top of one of the cans. Connect each terminal to a separate can, mounting the cans close together with the pop-top suspended between them (see picture). Turn the crank and observe the behavior of the suspended pop-top. Ben Franklin used one of these devices connected to his house roof so that he would be alerted when the air was highly-charged.

g. Charge a Leyden Jar with your Wimshurst Machine! (Be careful as this demonstration can be very dangerous!) Connecting the top terminal to the Wimshurst Machine, place the Leyden Jar on an insulated surface and crank the machine for a minute. After charging, discharge the Leyden Jar with a pair of insulated tongs and observe the “thick, white” spark produced. Students will witness an impressive spark of high voltage AND higher current than the Wimshurst alone. DO NOT allow ANY student to touch the Leyden Jar when it is charged!

Part 3 – The Tesla Coil

A Tesla Coil is a type of transformer invented by Nikola Tesla around 1891. It is used to produce high voltage, low current, high frequency alternating current electricity, stepping up ordinary 110-volt electricity to 10,000 to 50,000 volts. Tesla used these coils to conduct innovative experiments in electrical lighting, phosphorescence, x-ray generation, electrotherapy, and the transmission of electrical energy without wires for broadcasting, and the transmission of electrical power.

The YouTube video uses the “Super Mario Brothers” theme in stereo and harmony on two coils and shows a performance on matching solid state Tesla coils operating at 41 kHz. The device has been named the Zeusaphone, after Zeus, Greek god of lightning, and as a play on words referencing the Sousaphone.

Versions of the Tesla Coil are widely used as igniters for high power gas discharge lamps, common examples being the mercury vapor and sodium types used for street lighting. Blue-violet plasma filaments produced from a Tesla Coil can be seen as a result of the ionization of air due to the high voltage from the Tesla Coil. More familiar to students is the “Plasma Globe science toy” which uses a low power variation of the Tesla Coil to ionize gases within the globe. Tesla Coils have been used in “Star Trek” movies for special effects and used a glass-plate-type of plasma globe in the most recent “star Trek” film.

Although a Tesla Coil produces relatively high voltages associated with low currents, it is not advisable to allow students to take direct shocks from these devices. While the voltage is high, the current is low, and since high-frequency currents travel almost entirely at the surface of a conductor, the current does not produce much of a shock when passing through the body. However it will burn the skin at the point where the spark strikes it. Any heart electrical abnormalities could be affected by the coil. It is safe, however, for simple experiments in the classroom to illustrate the effects of high voltages.

a. A Tesla Coil will generate sparks and corona of

course, because of the high voltage created. Place a fluorescent light tube held in one hand or on a lab table will light when the high-frequency spark jumps to one end of it with no wires. Even a burned-out fluorescent light tube will glow when the Tesla Coil is held nearby.

b. A 300- to 500-watt incandescent light bulb

produces a very beautiful effect when the Tesla Coil is placed on a lab table in the dark and placed so the spark jumps to the base of the bulb. This effect is similar to the commercially-made plasma globes that are popular in science catalogs and novelty stores. The gas within the bulb becomes ionized by the high voltage and characteristic blue plasma streamers are generated within the bulb from the wires and bulb filament.

c. Small neon bulbs or gas tubes will glow with their characteristic color when a spark is generated. This is a great example of spectroscopy and how each gas exhibits its signature color when excited by a high voltage.

d. Two parallel stiff copper wires can be positioned

vertically and bent so that they are separated slightly as the wires rise, a “Jacob’s Ladder” can be constructed. As the Tesla Coil is touched to the wires, a violet spark is generated across the gap between the two wires and will rise due to the heating of the air as the spark is produced. This effect has been used for years in monster B-movies as “mad scientist” lab equipments. It is a great effect to demonstrate to your students. Wear a crazy wig and play a little horror movie music to add to the effect!

## Dissectible Leyden Jar

In Stock SKU: P6-3380
\$14.00

In Stock SKU: P6-3350
\$79.00

## Tesla Coil

In Stock SKU: P6-3550
\$253.00

## Voltas Hail Storm

In Stock SKU: P6-3320
\$77.00

## Fun Fly Stick Science Kit

In Stock SKU: 11-0051
\$29.95

## Electricity, Wavelength, and Energy

 Looking for a Hands-On Activity to Excite your Students about Learning Electricity?In this issue of CoolStuff we have just the thing! A series of hands-on electricity activities that students can use to to explore key electricity concepts. No matter what level students you teach, elementary, middle school, or high school; we have something for everyone. Real life electricity investigations where your student’s see, hear, and feel actual results in electronic configurations. High School LevelThe electromagnetic spectrum chart shows that the frequency of light increases as you travel up the chart from infrared light through the visible spectrum and beyond. We also know that it takes more energy to produce higher frequencies of light. Now you can demonstrate this relationship with the Genecon and a few inexpensive parts. Click the image to watch the video and get more information. Elementary – Middle School LevelThe production of electric current is a mystery to many students. The Genecon provides a hands-on solution to this problem. Students can feel the extra work it takes to light up bulbs and see that current flows in different directions as they charge a capacitor and watch it discharge. Click the image to watch the video and get more information.

## The Real Simple Motor

You’ve seen the World’s Simplest Motor™.

Now you can make one that’s even simpler than that, with materials you probably already have on hand! Just a battery, magnet, copper wire and some washers is all it takes.

The World’s Even More Simple Motor

How it Works …

This simple Homopolar Motor shows how moving charges (an electric current) experience a force when they move through a magnetic field. When the wire is in place, current flows from the battery’s positive terminal, through the wire, radially through the magnet, and into the battery’s negative terminal.

The direction of the force is perpendicular to both the direction of the current and the direction of the magnetic field, as demonstrated by the Left Hand Rule.

• The magnetic field is vertical, relative to the table.
• The current is radially inward at the lower point of contact, toward the center of the battery.
• The resulting force on the current-carrying wire is tangential. The tangential force, or torque, causes the wire to rotate.

Note that only one connection to the magnet is necessary for the motion to occur. Creating two connections doubles the resulting force, creating a faster spin. Try bending the wire into different shapes, such as a spiral that rests one end on the positive terminal and curls around the battery.

FAQ’s

1. Can I use any size wire? Any copper wire that holds its shape will work, but thicker wire is better for two reasons. First, it his heavier and less likely to flip out of place. Secondly, thicker wire has lower internal resistance and will not get as hot after conducting electricity.

2. Will ceramic disk magnets work? No. The magnet must be made of a conducting material.
Will it spin faster if I use a bigger battery (or more batteries)? Probably not, but it might last longer.

3. Will it spin faster if I use a bigger battery (or more batteries)? Probably not, but it might last longer.

4. I’ve seen other versions without washers. What is the purpose of the washers? Al Gibson (Rochester Adams High School, retired) told us about the washers. The bottom one adds stability, and the top ones keep the wire from sliding off. You can try it without them.

5. What does Homopolar mean? This motor is homopolar because there is no change of polarity in the wire. The Worlds Simplest Motor ?, by comparison, interrupts the current (and the magnetic field) every half-turn. More efficient motors employ a commutator, which reverses the coil’s polarity with every half-turn.

6. Where can I get the parts? Right here!

Get Supplies here:

Enough supplies for 10 motors!

## Homopolar Motor Kit

In Stock SKU: P8-8350
\$19.00