The History of Electricity! It’s Shocking!!!! Lesson 1: Unit 1

The effects of static electricity were first observed about 2500 years ago in ancient Greece. Amber, a fossilized resin from trees, was used by the Greeks for barter and for decoration. The Greeks noticed that when amber was rubbed with cloth, the amber would attract and pick up bits of dust, feathers, hair or other light material. The attractive nature of rubbed amber was not yet understood.

2000 years later, the curious effects of rubbed amber and other materials were investigated systematically by an English scientist named Dr. William Gilbert ( ) Dr. Gilbert was the personal physician to Queen Elizabeth I. Gilbert noticed that amber and other materials would attract small objects if they were rubbed with appropriate fabrics. Gilbert used the word electrified for materials that, when rubbed together, showed the attractive property of amber (1 fluid model)

The Greek word for amber is elektron. Modern words such as electron, electrified, electricity, and electronics all come from the Greek word for amber. More than 100 years passed before French scientist Charles Du Fay (1698 – 1739) showed that there are actually two kinds of electrical charge. Charles Du Fay noticed that two pieces of amber, when rubbed with fur, repel each other. Two pieces of glass, when rubbed with silk, also repel each other.

However, if ‘electrified’ amber is brought near ‘electrified glass’ the amber and glass attract each other. Du Fay concluded that there must be two kinds of electricity. Du Fay classed the charge on amber resinous electricity (because amber is hardened resin); he called the charge on glass vitreous electricity. Eventually these names were replaced with negative and positive electricity. (2 fluid model)

The terms positive and negative electricity were first used by the American Benjamin Franklin ( ). Franklin actually thought there was only one kind of electricity. In his view, an excess of electricity was positive; a shortage of electricity was negative. His theory was incorrect, but the terms positive and negative are still used today.

Models of Electricity Scientists use Observations about nature to construct models and theories to explain how nature works. These models can change over time when new observations are made. This is what happened to the theory that explains how electricity works.

In the 1600’s, the theory to explain how electricity was called the one-fluid model. William Gilbert suggested that electricity was a fluid that could flow between objects.

A brief chemistry lesson… All matter is made up of atoms. Atoms are made of: neutral neutrons Positive protons Negative electrons Protons and neutrons are stuck in the middle and do not move. Electrons are located in orbits and can move from atom to atoms.

Benjamin Franklin explained that positive and negative charges were due to the electric fluid. When an object lost fluid it became negatively charged, and when it gained fluid it became positively charged.

Just Enough Fluid Too little fluid Too much fluid

Over time the theory changed because of new observations by DuFay. The two-fluid model of electricity was suggested. This model used two types of fluid instead of just one. One of the fluids was thought to be positively charged while the other was negatively charged.

An object could gain a positive charge by either gaining positive fluid or losing negative fluid. An object could gain negative charge similarly.

Du Fay’s Theory Two Fluids Equal amount – neutral Two Fluids More blue – negative Two Fluids More Red – positive Attracted Objects Trading fluids

Then, in 1897 J.J. Thomson discovered the electron (which you will learn about A LOT in the chemistry unit) This meant that the model of electricity had to be changed again, to pretty much what we use now. This is called the particle theory of electricity

Remember that an atom is made up of a nucleus containing protons and neutrons. The nucleus has an overall positive charge. Spinning around the positive nucleus are electrons, which are negatively charged.

The particle model of electricity states that when two objects are rubbed together, electrons are removed from the atoms of one object and move to the second object, it becomes negatively charged. The first object is positively charged because it is missing some electrons. NOTHING in the nucleus moves! Negatively charged electrons move, while positive charges are stuck where they are.

Some atoms hold their electrons loosely while others hold on tight.

Particle Model of Electricity (Electron Theory) Facts KNOW THESE! MEMORIZE! 1. There are two kinds of charge, positive and negative. 2. Charge is conserved, it cannot be created nor destroyed. 3. A neutral body has an equal number of positive and negative charges.

Particle Model of Electricity (Electron Theory) 4. Positive charges are fixed (cant move) and negative charges (electrons) are free to move. 5. An excess of negative charges indicates a negatively charged body. A deficit of negative charges leaves a positively charged object.

Particle Model of Electricity (Electron Theory) 6. Charge is shared by contact. Materials which allow charges to move easily are called conductors. Materials in which charges do not move easily are called insulators. 7. Like charges repel and unlike charges attract.