Otis Singleton
Benjamin Franklin is often remembered for his work with electricity, but he did not discover electricity. Instead, Franklin contributed significantly to our modern understanding of it. He is known for his famous kite and key experiment, which demonstrated the connection between lightning and electricity. Franklin also introduced terms like electric fire to describe electricity as a common element with fluid-like properties that passed from one body to another without being destroyed. He designed instruments, such as the lightning rod, and conducted experiments with Leyden jars and wires, creating the first electric circuit and series-connected electric source. Franklin's work laid the foundation for the single fluid theory and the concept of the conservation of charge.
| Characteristics | Values |
|---|---|
| Date of kite experiment | June 1752 |
| Location of kite experiment | Philadelphia |
| Purpose of kite experiment | To demonstrate the electrical nature of lightning |
| Materials used | Kite, hemp string, silk string, house key, Leyden jar, sharp wire |
| Assistants | Son William Franklin, Joseph Priestley |
| Outcome | Picked up the ambient electrical charge from the storm |
| Contribution to understanding electricity | Introduced terms like "attraction" and "repulsion", Coined the term "electric fire" to describe a "common element" of electricity, Developed the lightning rod, Created the first electric circuit |
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What You'll Learn
Benjamin Franklin's kite and key experiment
On a stormy June afternoon in 1752, Benjamin Franklin performed his famous kite experiment. Franklin's aim was to demonstrate the electrical nature of lightning. He constructed a simple kite with his son, William, using a large silk handkerchief, cedar wood, a hemp string, and a silk string. A sharp, pointed wire was attached to the top of the kite to act as a lightning rod, and a metal house key was tied to the hemp string. Franklin also had a Leyden jar—a device that could store an electrical charge—to complete his setup.
As the kite flew in the thunderstorm, the hemp string became wet and conducted an electrical charge quickly, while the silk string remained dry and did not conduct electricity. The negative charges from the cloud were drawn to the kite, string, key, and Leyden jar. When Franklin moved his hand near the key, he received an electric shock as the negative charge attracted the positive charge in his body.
Franklin's experiment successfully demonstrated the connection between electricity and lightning, leading to a better understanding of positive and negative charges. It also resulted in the invention of the lightning rod. Despite the fame of this experiment, it is important to note that Benjamin Franklin did not discover electricity during this or any other experiment.
The exact details of the experiment have been questioned by historians, and Franklin himself never wrote a detailed account of it. The story has become legendary, with some aspects remaining unclear or "dim and mystifying," as Pulitzer Prize-winning biographer Carl Van Doren described it. However, it remains a notable example of Franklin's scientific curiosity and his contributions to our understanding of electricity.
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Franklin's discovery of lightning rods
While Benjamin Franklin did not discover electricity, he did contribute significantly to our modern understanding of it. One of his most famous experiments, the kite and key trick, demonstrated the connection between lightning and electricity. This experiment also helped Franklin develop the lightning rod, a device used to protect buildings from lightning damage.
Franklin's kite experiment took place in June 1752 in Philadelphia. As a thunderstorm rolled in, Franklin and his son William flew a kite with a key tied to the string. The kite was constructed with a wire attached to the top to act as a lightning rod, a hemp string that would conduct an electrical charge quickly when wet, and a silk string that would stay dry. When the key began to receive an electrical charge from the air, Franklin knew that lightning was a form of electricity.
Franklin's kite experiment was not without its dangers. If the kite had been struck by lightning, Franklin likely would have been electrocuted. However, the experiment was a success, and Franklin went on to perfect his lightning rod invention. He described the ideal lightning rod as an iron rod about 8 to 10 feet long, sharpened to a point at the end. This design has stood the test of time and remains the basis for all modern lightning protection codes.
In 1753, Franklin published a method for protecting houses from lightning damage using lightning rods in Poor Richard's Almanack. He suggested using a small iron rod, with one end buried three or four feet in the moist ground and the other end extending six to eight feet above the highest point of the building. This design allowed lightning strikes to be transported harmlessly to the ground. Soon, Franklin's lightning rods could be found on buildings from New York to Boston, London to Paris.
Franklin's discovery of the lightning rod was an important contribution to the understanding of electricity and its practical applications. It revolutionized human perceptions of the natural world and demonstrated how basic, curiosity-driven research can lead to significant benefits.
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His introduction of the terms 'attraction' and 'repulsion'
In the 1700s, scientists were still trying to understand the natural properties of electricity, such as attraction and repulsion. Before Benjamin Franklin's experiments, the main explanation for electrical attraction and repulsion was that electrified bodies gave off an effluvium, or a small stream of particles that flows from an electrified object without changing its weight or bulk.
Franklin began his electrical experiments in 1746 and, by 1750, had developed a one-fluid theory of electricity. He imagined electricity as a type of invisible "electric fluid" present in all matter and coined the term "electric charge". Franklin believed that rubbing insulating surfaces together caused this fluid to change location and that a flow of this fluid constituted an electric current.
Franklin also introduced the terms "positive" and "negative" to describe the charges acquired by a glass rod when it is rubbed with silk or a rubber rod with fur. He observed that like or similar charges repel each other, while opposite charges attract each other. In a letter to Peter Collinson, Franklin wrote:
> "We say B (and other Bodies alike circumstanced) are electricised positively; A negatively; Or rather B is electricised plus and A minus ... These terms we may use till philosophers give us better."
Franklin's work became the basis for the single fluid theory of electricity.
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Franklin's work on the single fluid theory
Benjamin Franklin is best known as a Founding Father of the United States, but he also made significant contributions to the understanding of electricity. Before Franklin's experiments, it was thought that electricity consisted of two opposing forces. Franklin's single fluid theory, also known as the unitary or one-fluid theory, imagined electricity as an invisible fluid.
Franklin's theory, first outlined in a letter in 1747, stated that electricity should be thought of as the movement of a single liquid, as opposed to the interaction between two liquids. He argued that all bodies contain a single fluid, which exists in a neutral state unless frictional forces cause an imbalance. When there is an excess of fluid, it has a positive charge, and when there is a lack of fluid, it has a negative charge. This theory explained how charges could be dispelled and how they could be passed through a chain of people. For example, he argued that the Leyden jar, a basic charge-storing device, became positively charged on the wire and inner surface and negatively charged on the outer surface. This caused an imbalance in fluid, and a person touching both portions of the jar allowed the fluid to flow normally.
Franklin's theory was a simpler alternative to the two-fluid theory proposed by Charles François de Cisternay du Fay, which postulated that electricity was the interaction between two electrical fluids: vitreous and resinous. Du Fay's theory was supported by many European natural philosophers, but Franklin's single-fluid theory soon became the most widely accepted theory of his time. It was easy to understand and provided a new way of thinking about electricity, even though it was later proven untrue. Franklin's work on the single-fluid theory was one of his most important scientific breakthroughs and helped lay the foundation for our modern understanding of electricity.
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His experiments with Leyden jars
Benjamin Franklin is known for his experiments with electricity, including his work with Leyden jars. Invented in 1745 by Pieter van Musschenbroek, the Leyden jar was an important invention for studying electricity. It could store large amounts of static electricity, and the more it was charged, the stronger the voltage became.
Franklin's experiments with the Leyden jar helped him understand the nature of electricity. In one experiment, he used a Leyden jar to collect "electric fire" or electricity, which he could then discharge at a later time. This experiment, which he described in the Pennsylvania Gazette in 1752, demonstrated the connection between lightning and electricity.
Franklin also made some interesting discoveries about the Leyden jar itself. In a letter from April 1748, he described some experiments that showed that a charged Leyden jar always has charges of opposite signs on the two conductors and that the charges are of the same magnitude. This meant that the Leyden jar contained a certain amount of electrical fluid before and after charging, and the charge was not actually being added or removed.
Franklin also proved that the glass itself was responsible for the power of the Leyden jar to give a shock. He did this by eliminating all other possible candidates, such as the water inside the jar, and showing that the jar could still give a shock even when the water was removed.
Franklin's work with the Leyden jar was an important contribution to the understanding of electricity and helped lay the foundation for further research and applications in this field.
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Frequently asked questions
No, he did not discover electricity, but he did contribute significantly to our modern understanding of it.
The kite experiment demonstrated that lightning and electricity are the same.
Franklin wanted to demonstrate the electrical nature of lightning, and to do so, he needed a thunderstorm.
Several artists have famously depicted Franklin and a boy flying a kite in a field during a dramatic storm. In these depictions, a bolt of lightning strikes the kite, shooting an arc of light from the key to Franklin’s finger.
The experiment was extremely dangerous, and Franklin and his son risked electrocution.
