Question #63

The Wimshurst Machine

The Leyden Jar

A leyden jar is a 1746 device that is still very known today. It was first created by the Dutch physicist Pieter van Musschenbroek of the University of Leyden and Ewald Georg von Kliest of Pomerania, working separately. However, today, most of the credit of the device is given to Pieter.
A leyden jar is made up of a glass jar with an outer and inner coating of metal which covers the bottom and sides of the jar almost up as far as the neck. Sealing the jar is a wooden stopper with a brass rod through the center of it. This brass rod has a ball at the external end of it and connects internally with the metal coating through a loose chain. This is shown in the picture above. When a charge is applied to the knob at the end of the rod, positive and negative charges emerge from the metal coating on either side of the jar. However, they are not able to discharge because of the glass between them. This means that there are two conductors (the metal covering) which are separated by an insulator (glass). As a result, the positive and negative charges hold themselves together in equilibrium until a grounding force is applied. This results in a storage of electricity. To use this electricity, the two conductors must be somehow connected, either with a wire which would allow the use of this electricity, or with a hand which could result in a serious shock. It was the very first capacitor.
The Wimshurst Machine was created by an Englishman named James Wimshurst who was part of the shipping business for the British Board of Trade. Today, however, he is known for his work in improving the Voss’ electrostatic generator. He changed the design so that the disks of the machine contra-rotate. The metal foil portions on the disks induce charges on each other which can be taken off by small, metal brushes and stored within the Leyden jars mentions above. The Wimshurst machine works through the quantum effect in that when two different conducting metals touch each other, a small current is transferred between them because of the different number of electrons in their atoms. This is able to occur on this machine when the sectors in the disk pass through one of the charge neutralizers. Once this occurs, the sector becomes charged and when it passes by a sector on the other side of the disk, it results in an equal and opposite charge on that sector. The front disk has one charge and as it spins, it begins to create a negative charge on the other side of the disk. This also occurs with the lower part of the disks but reverse. Therefore, when the sector passes by the neutralizer bar, it becomes neutral and is ready to be charged again. As a result, there are low and opposite charges on the top and bottom and high and equal charges on the sides. The high charges are then transferred over to the layden jars attached to the machine which are then connected to the discharge terminals. After the voltage builds up, a spark occurs across the terminals and the cycle begins over again. The entire process is demonstrated in the clip listed below:
http://www.wimshurstmachine.com/

Sources:

http://www.powerlabs.org/wimshurst.htm

http://www.sparkmuseum.com/LEYDEN.HTM

http://www.thebakken.org/electricity/Leyden-jar.html

Question #63

Throughout history there have been many early sources that helped us study static electricity. One of the most earliest sources was the leyden jar. The main idea behind the leyden jar was the concept was to store electrical energy, most likely between two conductors. This device was invented by the brilliant Pieter van Musschenbroek in the year of 1745. It later became credited as the first capacitor, but was first referred to as a condenser. After energy was stored, it could be used to charge something. A leyden jar would have looked like the following.


Another notable invention was the Wimshurst Machine. This was a device that was created by James Wimshurst. It was invented around the year 1880. Unlike the other device, this one was used to generate electricity, not store it. It would later be referred to as an electrostatic generator. It was designed to have two roatating discs which allowed a current of electrons to be transferred between. Both of these inventions were notable in the field of electricity.

The Wimshurst Machine was developed between 1880 and 1883 by James Wimshurts. It is an electrostatic device created for the purpose of generating high voltages. It has two contra-rotating discs on a vertical spine with two cross bars, metallic brushes, and a spark gap. It is an influence machine because it creates electric charges through electrostatic induction. It is self-starting but does need mechanical power initially to rotate the disks. The current produced is constant and proportional to the size of the metals disks and the rate at which they are rotating. The Leyden Jar is an early storage device for electric charge. It was the first capacitor. 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. 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. Franklin invented his electric bells in the middle of the 18th century when noticed that a pith ball or cork would initially be attracted to a charged object, but if the two touched the ball would be repelled. He realized that this was because the two objects were initially charged differently but once they touched they took on the same charge. Franklin realized that if he replaced the charged object with a bell, he could make an "electric bell." He soon found practical use for his bell as a lightning detector. When connected it to his lightning rod, the bell would ring whenever an electrical storm was nearby.

Chapter 20: Question #63

Katie Shill
12 March 2008

Numerous research devices were used in the 17th and 18th centuries to study static electricity, including the Leyden jar and the Wimshurst machine. First, the Leyden jar was invented in 1745 by a man named Pieter van Musschenbroek. The Leyden jar was the first capacitor. A capacitor is an electronic device that can store energy in the electric field between a pair of conductors. The process of storing energy in the capacitor is known as "charging", and involves electric charges of equal magnitude, but opposite polarity, building up on each plate.
A battery of four Leyden jars:

Another invention used during this time period was Wimshurst machine. The Wimshurst machine is an electrostatic device for generating high voltages. It has a distinctive appearance with two large rotating discs mounted in a vertical plane, two cross bars with metallic brushes, and a spark gap formed by two metal spheres.
A Wimshurst machine with two Leyden jars:

Works Cited

chem.ch.huji.ac.il/instruments/archaic/leyden_jars.htm

www.wikipedia.org/

Question #63

The leyden jar was an early device created for storing charge. It was invented in 1745 by Peter van Musschenbroek. It was the first capacitor ever invented and was used in many early electricle experiments. The creation of this device pathed the way for further progresses in electricity and its storage.

The leyden jar worked by having an electrode connected to a foil inside of a jar. A conducting foil was rapped around the outside of the jar. Or the inside of the jar was partially filled with water. The water at first was used as a conducter, later they found that foil works better to collect the charge. The process was powered by an electrostatic generorator. The charge is stored in the glass of the leyden jar. The thinner the dielectric and the closer the plates were to each other increased the capacity at a certain voltage. It has later been found that the dielectrics were not neccesarry but just increased the capacity and prevented arcing between the plates.

The leyden jar was a break through in the storage of electricity. This discovery eventually led to the modern capacitor.

Tuesday, March 11, 2008

Today in class we talked about action at a distance.  The electrostatic force is an example of action at a distance.  Non contact forces are action at a distance forces.  Gravity is another example of action at a distance forces.  A diagram was given of an electroscope.  A charged balloon was moved toward the electroscope and it acted on the electroscope at a distance.  Action at a distance forces are also known as field forces.  An electric charge creates an electric field.  This field alters the space around it.  The magnitude of electric field strength is equal to force per unit changed.  The direction of the force exerted on a positive test charge.  The electric field is made up of a single point charge; either positive or negative, a charged conducting sphere, or two point charges; both either negative or positive, and a pair of charged parallel plates.  The point charge equals all charge concentrated at a point.  A charged conducting sphere acts as though all the charge were concentrated at the center.  A field within a charged conducting sphere is zero.  The same principle is used in the faraday cage.  A diagram of a pair of positive point charges, a pair of negative point charges, and one point charge that is negative and one that is positive.  The electromagnetic field always runs in through the negative point charge and out through the positive point charge.  A diagram of charged parallel plates was shown.  The top plate was positively charged and the bottom plate was negatively charged.  The field was moving in a downward fashion, from the positive to the negative.  The intensity of electric field varies inversely with the square of the distance from the point charge.  The greater intensity seen by greater concentration of field lines.  Two diagrams showed how more lines indicated stronger electric fields and the way the way the field lines were when objects had unequal charges. 

Chapter 20 Question 63

Static electricity has been studied for a very long time, beginning in 600 BC. People discovered that when amber was rubbed with cat fur, pieces of paper were attracted to the amber. This basic knowledge was able to help later scientists in their studies of static electricity. People experimented with electricity by using conductors, and discovered that sparks, chains, and strips could pass to these conductors which joined the conductors to insulated glass globes (Electrical Machines History). Later, in the seventeenth century, Otto Von Guericke invented a machine that produced static electricity (Artwork LDC). Inside a glass globe, Von Guerbicke placed a sulfur ball mounted on a pole. This machine was rotated by a hand crank. When it was spinning, it rubbed against a pad which then generated static electricity sparks (Artwork LDC). This machine was the first electric generator.
During the eighteenth century, machines involving static electricity improved. One of these machines was the Ramsden Friction Machine. This machine was made up of a circular piece of glass which was on an axle. The machine was turned by a handle which allowed it to rub against two pads. This caused the machine to be electrified on two sides (Electrical Machines History). When the handle turned, the glass plate was charged positively. The plate repelled positive charges to the ends of the conductors and left parts of them with a negative charge (Electrical Machines History). Friction allowed the glass to be continuously positively re-electrified.
In 1772, a scientist by the name of LeRoy invented a machine that included two insulated cyllindric conductors that were placed horizontally. These conductors collected both positive and negative charges. One of the conductors was positively charged while the other was negatively charged (Electrical Machines History). Van Marum created another machine which was similar to Ramsden's. The object of the machine was to collect positive and negative charges (Electrical Machines History).

Works Cited:

Artwork LDC. Ottoman Von Guericke 1602-1686. About.com: Inventors. 2008. 11 March 2008. >.

Electrical Machines History. Sparks Museum Early Radio and Scientific Apparatus. 11 March 2008. <http://www.sparksmuseum.com/FRICTION_HIST.HTM>.

Kodiac1. Static Electricity. Urban Dictionary. 3 July 2006. 11 March 2006. >.