March 13 Class Notes

We went over the homework at the start of class. We then watched a video on electric fields and lines of force. The rest of class was spent working on problem set 2. We also recieved the answers to problem sets 1 & 2.

Leyden Jar

The Leyden jar was invented in 1745 by Pieter van Musschenbroek. It was the first capacitor that was used as a devide for storing electric charge and to conduct early experiments in electricity. A typical design consists of a top electrode electrically connected usually by a chain to a metal foil which coats part of the inner surface of a glass jar. An electrostatic generator charges the jar and is connected to the inner electrode while the outer plate is grounded. Wrapped around the outside of the jar is a conducting foil which matches the internal coated area. The jar has equal but opposite charges in the inner and outer surfaces of the jar. Originally, the device was just a glass bottle that was partially filled with water and had a metal wire passing through a cork closing it. However, it was soon discovered by Watson in 1746 that it was better to coat the exterior of the jar with metal foil. This was better because it left the impure water inside acting as a conductor, connected by a chain to a sphere (external terminal). Initially it was believed that the charge was stored in water and after further investigation by Benjamin Franklin it was concluded that the charge was stored in the glass—not the water. Today we know that the the charge is actually stored in a thin layer along the facing surfaces which touch the glass also known as the dielectric.

Chapter 20 Question 63

The Leyden jar was invented in 1745 by Pieter Van Musschenbroek. It was a device for storing an electric charge. The Leyden jar was the first ever capacitor. Leyden jars were mostly used to conduct early experiments in electricity.
The Wimshurst Machine was invented in the late 1800s by James Wimshurst. A Wimshurst Machine is a device for generating a high voltage electric charge. It has two large rotating discs that spin in the opposite direction to the other.

Question 63

The leyden jar was used by early experimenters to store electricity. The leyden jar consisted of an insulator with a layer of metal on the inside and the outside of it. The inside metal is given a charge with the outside metal being grounded. When this occurs the outside metal has an equal but opposite reaction. When the outside and inside metals are connected a spark occurs and both metals are grounded. Scientists today would call a machine like this a capacitator. In Wimshurst design, the disks contra-rotate. The metal foil sectors on the disks induce charges on each other, which are picked off with metal brushes and stored in Leiden jars. The machine was developed to form high voltages in the late 19th century. The positive feedback of the Wimshurst design increases the accumulating charges until the breakdown voltage of the air is reached and a spark jumps across the gap. Both of these designs were very successful during their time in studying static electricity.

The Electrophorus took the place of the Leyden jar and is the two-plate principle that is behind the electrical condensers in use today. Invented in 1775 by Alessandro Volta, its purpose was to create and store an electrostatic charge.
What does it consist of? The electrophorus consists of a dielectric plate (originally a 'cake' of resinous material like pitch or wax, but in modern versions plastic is used) and a metal plate with an insulating handle.

The Van de Graaff generator was invented in 1929 by Robert J. Van de Graaff and is one of the most famous of all the electrostatic devices. It uses a conveyor belt to carry an electric charge from a high-voltage supply to a hollow ball. Another generator was modified to produce x-rays to be used in treating internal tumors in Boston in 1927. Van de Graaff's first generator operated at 80,000 volts and eventually would be improved to five million volts. This generator remains one of the most widely used experimental exhibits in schools and museums today.
Why did it come about? Van de Graaff needed to accelerate subatomic particles to a very high velocity to test the properties of atoms. He knew that by storing an electrostatic charge, could result in many benefits. -DH

18th & 19th Century Static Electricity Devices

The Layden jar (above) was invented by Pieter van Musschenbroek in 1745 and named after the Universityof Leyden in the Netherlands. The jar was originally a sealed glass jar with a wire running through the cork seal and into the water within the bottle. The bottle had a conuctor wrapped around it. Later the water was replaced by a coating of conducting metal around the inside of the jar. The bottle can store the charge passed in through the wire on the thin layer of conductor around the inside of the jar, which is called a dielectric.

The Aepinus condenser (below) was invented by Franz Aepinus in 1789. Today, condensers are known as capacitors, which store energy between to plates. The condenser was used to demonstrate conduction and induction. It was designed so that the two plates could be moves, and the plate could be replaced with a different material. It was the first condenser created after the Leyden jar.

Leyden Jar

In 1746, Pieter Van Musschenbroeck invented a small device that could store a large electric charge. He called this device the Leyden Jar and it was used to perform many experiments in electricity during the seventeenth and eighteenth century. 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. The role of the outer plate was provided by the hand of the experimenter. Soon it was found that it was better to coat the exterior of the jar with metal foil, leaving the impure water inside acting as a conductor, connected by a chain or wire to an external terminal, a sphere, to avoid losses by corona discharge. It was initially believed that the charge was stored in the water. Ben Franklin investigated the Leyden Jar, and concluded that the charge was stored in the glass, not in the water, as others had assumed. (wikipedia)

#63 - Sarah S.

Wimshurst

Leiden

The Leiden Jar
History: 1745 - Ewald Kleist, stored large amounts of electric charge by lining a glass jar with silver foil, and charged the foil with a friction. He received a shock. 1746 - Dutch physicist Pieter van Musschenbroek of the University of Leyden made the same discovery
Consists of: A glass cylindrical container (jar) with an outer and inner metal (foil) coating covering the bottom and sides of an insulator (plastic or glass).
Brass rod with an external knob passing through a wooden stopper that is connected to the inner coating by a loose metal chain.
How it works: an electrical charge is applied to the external knob and positive and negative charges accumulate from the two metal coatings respectively. However, they are unable to discharge due to the glass between them. The result is the charges will hold each other in equilibrium until a discharge path is provided. Charge is stored not in the conductors but in a thin layer along the facing surfaces that touch the glass. When the outside and inside surfaces are connected by a conductor there is a spark and everything is grounded.
Uses: store electricity in experiments and a condenser in early wireless equipment.

The Whimshurst Machine
History: developed between 1880 and 1883 by James Wimshurst
Consists of : with two large contra-rotating discs mounted in a vertical plane, two cross bars with metallic brushes, and a spark gap formed by two metal spheres.
How it works: creates electric charges through electrostatic induction
two insulated disks and their metal sectors rotate in opposite directions, metal foil sectors on the disks induce charges on each other, which are amplified and collected by metal brushes and stored in Leiden jars, spark jumps across gap
machine is self-starting (no external electrical power required to create the initial charge). Does require mechanical power to turn the disks against the electric field (this is the energy that the machine converts into electric power). The output is a current proportional to the area covered by the metal sectors and to the rotation speed.

Becky Salisbury

The Leyden jar was a device invented in Pieter van Musschenbroek in 1745 that was used for storing electric charge. It was one of the earliest inventions used for experiments in electricity. In respect to the design of the Leyden jar, the outer plate was grounded whereas the inner and outer surfaces of the jar stored equal but opposite charges. Benjamin Franklin was actually studying the Leyden jar, and was the first to realize that the charge was actually stored in the glass and not the water inside the jar. The storage ability or capacitance of the Leyden jar is about 1 farad, an SI measuring unit of capacitance. This great invention was one of the first inventions which helped scientist study static electricity.

Question 63

Although there were several devices used in the seventeenth and eighteenth centuries to study static electricity, the two most well known were the Leyden jar and the Wimshurst machine. The quest for more knowledge involving static electricity was a theme of these two centuries. First off, the Leyden jar was discovered, accidently, by a Dutch physicist by the name of Pieter van Musschenbroek in 1745. The Leyden jar contained an electrode located at the top that was then connected with some kind of conductor to the inner surface of a glass jar. The charges on the inside and outside differ with whether or not they are positive or negative, but in any case there is an equal amount of them. At first water was used in the inside to be created as a means of travel for the condcutor, but later it was discovered that wrapping the glass with metal foil was a better method.

The Wimshurst machine creates static electric sparks when cranked. It is made of two plastic discs, each with spaced out metal sectors. This machine has to supporters on either side and contains a hand wheel used to crank and operate this piece of science equiptment. It also comes with induced charge collecting enablers and Leyden jar capacitators to help maximize its static electric sparks and effectiveness. The hand crank allows for the sparks to happen.

#63

  The Layden Jar is an early device for storing electric charge that was invented in 1745 by Pieter van Musschenbroek. It was the first capacitor. It consisted of a top electrode electrically connected to metal foil coating a glass jar and a brass knob at the end. When an electrical charge is applied to the external knob, positive and negative charges accumulate from the two metal coatings respectively, but are unable to discharge because of the glass between them. The result is that the charges will hold each other in equilibrium  until a discharge path is provided.  These were first used to store electricity, but were later used as a condenser in early wireless equipment.

The Wimshurt machine is as electrostatic device for generating high voltages developed in 1880. It has two large contra-rotating discs mounted in a vertical plane. Their metal sectors rotate in the opposite direction passing the crossed metal. An imbalance in charges is induced, amplified, and collected by two pairs of metal combs. The positive feedback increases until the breakdown voltage of air is reached and a spark jumps across.

 

History of Science - Leyden Jar

The concept of the leyden jar was invented by the ancient Greeks and then expanded on by a German scientist in 1745. A typical design consists of a top electrode connected, by a chain, to a metal foil, coating part of the inner surface of a glass jar. A conducting foil is wrapped around the outside of the jar. The jar is charged by an electrostatic generator connected to the inner electrode while the outer plate is grounded. The inner and outer surfaces of the jar store equal, but opposite charges. Leyden jars are typically used to build and store electricity and is currently known as a capacitator.

? # 63

Technology was lacking in the seventeenth and eighteenth centuries compared to what is available at our fingertips today. Even so this time period had its share of science innovation. For example, in science there were ways that scientists were able to study static electricity. One of the ways they were able to do so was the Leyden jar. The Leyden jar is constructed with a glass jar that has an electrode attached to a piece of foil inside of it. Plus, there is a conducting foil is wrapped around the outside of the jar, matching the internal coated area. Finally the whole device is completed by charging it with generator. The jar works by holding the charges from the generator as they are equal but opposite.

March 4th Scribe

First we went over the test, then we found out that test corrections were due on the 5th because five week grades were due at that time as well. Then Mr. Wirth asked the question, What do you know about electricity? Their were very few responses, but the class was eager to learn the wonders of electricity. In the beginning of class we did some amber demos. then we used the rubber and glass and rubbed them against silk and fur to see the power of static electricity. This is where we found out that opposites attract and that water attracts to both rubber and glass. Then we learned about the electroscope, and how positives repel each other. Next Mr. Wirth showed us the magic water and how it attracts and repels to different materials. It is important to know that static electricity is not actually static, it is in fact moving. Also, electricity comes from matter. Another important fact to remember is that protons never leave because that would change the atomic number of the atom. Hopefully for anyone that needed a refresher or was not in class, this will be an effective tool.

03/07/08 What happened?

Some people might be asking themselves, What happened friday? I hope I can answer some of the questions regarding 5th period...the rest is up to you to remember.

The beginning of the class was revolved around checking the homework with the answers up on the overhead. Like many Fridays, it was a pretty talkative group. Conversations about physics related things of course. After about ten minutes or so of homework talk, Mr. Wirth went on to explain the mini-lab that the class was going to work on that day.

First, Mr. Wirth charges up the ruler with wool, making the ruler negative.
Next he charges the rod with the bunny skin, making the rod negative.
The reaction of two negatively charged objects to each other is <-----> repulsive.

The class broke up into groups to conduct similar experiments with the same objects to see how different charges and objects react to one another. Data was recorded in a chart and one chart was necessary per group.
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After the groups returned back to their seats, Mr. Wirth passed out graded work and showed us our weekend homework...
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Read Chapter 20 (p. 540-561)
Do problems: #1, 5, 6, 16, 18, 19, 21
DUE: Tuesday, March 11th*
*Students can either hand write or type up the homework and it will be collected and be graded.
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There is a online version of the textbook located on the physics website in the side tool bar on the homepage if you can't find your own book.
Make sure to know how to use an electroscope, if not be sure to see Mr. Wirth with questions.
That's about it. Enjoy.
-DH