Light and optics

 

Light and optics

Light is the kind of energy that makes it possible for us to see. Without light there would be no life on earth. Green plants use the sun’s light to grow and produce food. In this process they produce oxygen, which we need to breathe. Without plants there would be no animals or food.

Light also provides us with fuel. The energy that the sun has sent to earth for millions of years has been stored in plants and then changed into coal, oil and gas – energy that we use today to operate machines and produce electricity and power.

We also get heat from the sun. Without it our planet would be so cold that nothing could live on it. 

Sources of light

All light comes from atoms, tiny particles that make up everything in our universe. When atoms gain energy they give it off as light. An atom that has such energy is called excited.

Some light is natural , like sunlight or light from stars . Other light is produced from things people make, like lamps or flashlights. A light bulb glows because electricity heats a wire inside. Candles produce light from fire when you light them. Lasers are devices that produce powerful beams of light in which all particles have the same energy and travel in the same direction.

There are certain substances that glow in the dark. Their atoms are excited for a certain time and after that they release light. Some insects, like fireflies glow naturally.

Nature of light

For a long time scientists were not sure about how light travels through space. Some thought that light behaves like a wave, others claimed that light particles travel in a straight line. Today, scientists agree that light is an electromagnetic wave made up of electrical and magnetic forces that travel through space at a very high speed. However, light is also a stream of particles called photons, which travel like a beam.

Light waves can be compared to waves in water. They have a wavelength, frequency and amplitude. The wavelength is the distance between the two highest parts of a wave, the frequency is the number of times that a wave passes a certain point every second, and the amplitude is the distance between the highest and lowest points of a wave. 

Electromagnetic waves

Not all electromagnetic waves are visible. Light refers to those waves that we can see.

Light that comes from the sun is basically white. It is made up of all colours. When it passes through a specially shaped glass called a prism it breaks up into different colours. When the sun comes out while it is still raining, we often observe a rainbow because light must pass through raindrops. It breaks up into all the colours of the visible spectrum. Violet light is at one end of the spectrum because it has the shortest wavelength, red light, which has the longest wavelength, is at the other end.

Ultraviolet rays are invisible waves with shorter wavelengths. They cause sunburn and may lead to skin cancer. In small amounts these rays have a good effect on our skin because they produce vitamin D. X rays are even shorter rays that can penetrate a human body. Doctors use them to take pictures of bones and other inside organs.

Waves with lengths longer than red light are called infrared rays. When you stand in front of a fire you feel warm, largely because infrared light is shining on you. Microwaves and radio waves are even longer. Microwaves are used to make food warm. Radio and TV stations broadcast programs by sending out radio waves, which may have a wavelength of up to a few meters.

How light behaves

When light waves strike an object three things may happen. The light can be reflected, absorbed or it may change its direction.

What happens to light depends on the kind of object or material that it hits. Transparent objects, like glass, let light waves pass through without mixing them up. You can see through this material. Translucent material also allows rays to pass through, but it mixes them up so that you cannot see through such objects clearly. Opaque materials don’t let any light pass through. 

Reflection

Most objects do not produce their own light. You can see these objects because light from the sun or from a lamp bounces off them and then travels to your eyes.

Some objects reflect little light, others, like mirrors or water reflect almost all the light because they are smooth and flat. The rays bounce off in only one direction. Reflected light also makes things sparkle and shine. When light shines on a normal object, like a tree, the rays bounce off in many directions.

 

Refraction

When light passes through an object it slows down because the molecules of a solid object are more densely packed than air molecules. It also changes its direction of travel – it refracts.

Example: Swimming pools do not look as deep as they really are because of the way light is bent. Water slows light down by about 25 per cent and glass slows it down even more. Light waves bend towards the glass, slow down and behind the glass resume their normal speed.

Another example is picking up a stone in water. The stone is not where you think it is. It appears to be farther away than it really is.

Scattering

Scattering shows us what happens when light rays hit atoms, molecules or tiny particles. These particles send off light in new and different directions. Most of the sky is blue because air molecules scatter more blue rays towards us than they do the other colours in sunlight. When the sun reaches the horizon in the evening it looks orange or red because the light that gets to us has lost so many of the other colours through scattering.

Colour

The colour of an object depends on the way it reflects and absorbs light. An object can absorb certain colours and reflect others. The colour that we see is a combination of all the colours it reflects, we can’t see the colours that it absorbs. An apple, for example, looks red because its surface reflects colours from the red end of the spectrum and absorbs the rest.

White objects reflect all colours of light, black objects absorb all colours.

How light is measured

Speed of light

Light travels fastest in empty space, where nothing can block its path. Its speed here is always the same: about 300,000 km per second. The light from the sun, which is about 150 million km away from the earth, reaches our planet in about 9 minutes.

Brightness

The brightness of light is measured in the unit candles, a name that dates back to the old days when wax candles were the only ways of lighting up a room. The amount of light that an object receives depends on how far away the light source is. If a simple candle shines directly on a flat surface that is one foot (about 30 cm) away light has an intensity of one foot-candle. An average 60 watt light bulb emits about 60 foot candles of light. In the metric system we measure the intensity of light in the unit lux. 1 lux is the light that shines on a flat surface one metre away.

Wavelength and frequencies

Scientists measure wavelengths in nanometres, which equals one billionth of a metre. Visible light ranges from 400 nanometres for violet light to about 700 nanometres for red light.

Frequencies are measured in a unit called hertz. A wave has a frequency of one hertz if one crest of the wave passes a checkpoint every second. Because visible light has a short wavelength and a high speed it has a high frequency, Violet light for example has a frequency of 750 trillion hertz. Radio waves, on the other hand have very low frequencies.

Electricity

 

Electricity

Everything is made up of atoms. Each one of them has three particles : protons, neutrons and electrons. Electrons spin around the centre of an atom. They have a negative charge. Protons, which are in the centre of atoms, have a positive charge.

Normally, an atom has as many protons as it has electrons. It is stable or balanced. Carbon, for example has six protons and six electrons.

Scientists can make electrons travel from one atom to another. An atom that loses electrons is positively charged, an atom that gets more electrons is negatively charged.

Electricity is created when electrons move between atoms. Positive atoms look for free negative electrons and attract them, so that they can be balanced.

Conductors and Insulators

Electricity can pass through some objects better than through others. Conductors are materials through which electrons can travel more freely. Copper, aluminium, steel and other metals are good conductors. So are some liquids like saltwater.

Insulators are materials in which electrons cannot move around. They stay in place. Glass, rubber, plastic or dry wood are good insulators. They are important for your safety, because without them, you couldn’t touch a hot pan or plug in a TV set.

Electric Current

When electrons move through a conductor an electric current is created. A current that always flows in one direction is called a direct current (DC). A battery for example, produces a direct current. A current that flows back and forth is called an alternating current (AC).

Electric Circuits

Electrons cannot jump freely through the air to a positively charged atom. They need a circuit to move. When a source of energy, like a battery, is connected to a light bulb the electrons can move from the battery to the light bulb and back again. We call this an electric circuit.

Sometimes there are many circuits in an electrical device that make it work. A TV set or a computer may have millions of parts that are connected to each other in different ways.

You can stop the current from flowing by putting a switch into the circuit. You can open the circuit and stop electrons from moving.

A piece of metal or wire can also be used to produce heat. When an electrical current passes through such metal it can be slowed down by resistance. This causes friction and makes the wires hot. That’s why you can toast your bread in a toaster or dry your hair with warm air from a hairdryer.

In some cases wires can become too hot if too many electrons flow through them. Special switches ,called fuses, protect the wiring in many buildings . 

Kinds of electricity

Static electricity

·         happens when there is a build-up of electrons

·         it stays in one place and then jumps to an object

·         it does not need a closed circuit to flow

·         it is the kind of electricity you feel when you rub your pullover against an object or when you drag your feet over a carpet.

·         lightning is a form of static electricity

Current electricity

·         happens when electrons flow freely between objects

·         it needs a conductor—something in which it can flow , like a wire.

·         current electricity needs a closed circuit

·         it is in many electrical appliances in our homes - toasters, TV sets , computers.

·         a battery is a form of current electricity

 How batteries work

A battery has liquid or paste in it that helps it produce electric charges. The flat end of the battery has a negative charge and the end with the bump has a positive charge.

When you link a wire between both ends a current flows. When the current passes through a light bulb electric energy is converted into light.

The chemicals in the battery keep the ends charged and the battery going. As times passes, the chemical becomes weaker and weaker and the battery cannot produce any more energy.

 How electricity is produced

Generators are used to transform mechanical energy into electrical energy. A magnet rotates inside a coil of wire. When the magnet moves, an electric current is produced in the wire.

Most power stations use turbines to make the generator rotate. Water is heated to make steam , which pushes the blades of the turbine. Gas, oil or coal can be used to heat the water. Some countries build power stations on rivers, where the moving water pushes the turbine blades.

 How electricity is measured

Electricity is measured in watts, named after James Watt who invented the steam engine. It would take about 750 watts to equal one horsepower.

A kilowatt-hour is the energy of 1,000 watts that work for one hour. If, for example, you use a 100-watt light bulb for 10 hours you have used 1 kilowatt of electricity.

 How electricity is transported

The electricity produced by a generator travels along cables to a transformer that changes the voltage of electricity. Power lines carry the high-voltage electricity over very long distances. When it reaches your home town another transformer lowers the voltage and smaller power lines bring it to homes, offices and factories.

 Electrical safety

 It is important to understand why and how you can protect yourself from electrical injuries.

Electric shock occurs when an electric current passes through your body. It can lead to heart failure and can damage other parts of your body. It can also burn your skin and other body tissues.

A very weak electrical object, like a battery, cannot do any harm to you, but inside the house you have devices and machines that use 220 volts.

Most machines in your house have safety features to protect you. It something goes wrong, a special wire leads the electricity to the ground where nothing can happen.

There are also electrical dangers outside your house. Trees that touch power lines can be dangerous. Lightning has more than enough electricity to kill a person. If you get caught in a thunderstorm stay away from open fields and high places. One of the safest places is your car, because lightning will only hit the outside metal of the car.

 

Marie Curie

Marie Curie discovered two new chemical elements – radium and polonium. She carried out the first research into the treatment of tumors with radiation, and she founded of the Curie Institutes, which are important medical research centers.

She is the only person who has ever won Nobel Prizes in both physics and chemistry.

Marie Curie’s Early Life and Education

Maria Salomea Sklodowska was born in Warsaw, Poland on November 7, 1867. At that time, Warsaw lay within the borders of the Russian Empire. Maria’s family wanted Poland to be an independent country.

Marie’s mother and father – Bronislawa and Wladyslaw – were both teachers and encouraged her interest in science.

When Marie was aged 10, her mother died. Marie started attending a boarding school, then moved to a gymnasium – a selective school for academically strong children. Aged 15, Marie graduated from high school, winning the gold medal for top student. She was passionate about science and wanted to continue learning about it.

Problems

Two obstacles stood in Marie’s way:

• her father had too little money to support her ambition to go to university
• higher education was not available for girls in Poland

Marie’s sister Bronya faced exactly the same problems.

To overcome the obstacles they faced, Marie agreed to work as a tutor and children’s governess to support Bronya financially. This allowed Bronya to go to France and study medicine in Paris.

For the next few years of her life, Marie worked to earn money for herself and Bronya. In the evenings, if she had time, she studied chemistry, physics, and mathematics textbooks. She also attended lectures and laboratory practicals at an illegal free “university” where Poles learned about Polish culture and practical science, both of which had been suppressed by the Russian Tsarist authorities.

In November 1891, aged 24, Marie followed Bronya to Paris. There she studied chemistry, mathematics, and physics at the Sorbonne, Paris’s most prestigious university. The course was, of course, taught in French, which Marie had to reach top speed in very quickly.

At first she shared an apartment with Bronya and Bronya’s husband, but the apartment lay an hour away from the university. Marie decided to rent a room in the Latin Quarter, closer to the Sorbonne.

This was a time of hardship for the young scientist; winters in her unheated apartment chilled her to the bone.

Top Student Again

In summer 1893, aged 26, Marie finished as top student in her master’s physics degree course. She was then awarded industrial funding to investigate how the composition of steel affected its magnetic properties. The idea was to find ways of making stronger magnets.

Her thirst for knowledge pushed her to continue with her education: she completed a master’s degree in chemistry in 1894, aged 27.

Homesick

For a long time, Marie had been homesick. She dearly wished to return to live in Poland. After working in Paris on steel magnets for a year, she vacationed in Poland, hoping to find work, but were no jobs for her.

A few years earlier she had been unable to study for a degree in her homeland because she was a woman. Now, for the same reason, she found she could not get a position at a university.

Back to Paris and Pierre

Marie decided to return to Paris and begin a Ph.D. degree in physics.

Back in Paris, in the year 1895, aged 28, she married Pierre Curie. Pierre had proposed to her before her journey back to Poland. Aged 36, he had only recently completed a Ph.D. in physics himself and had become a professor. He had written his Ph.D. thesis after years of delay, because Marie had encouraged him to.

Pierre was already a highly respected industrial scientist and inventor who, at the age of 21, had discovered piezoelectricity with his brother Jacques.

Pierre was also an expert in magnetism: he discovered the effect now called the Curie Point where a change of temperature has a large effect on a magnet’s properties.

Marie Curie’s Scientific Discoveries

The Ph.D. degree is a research based degree, and Marie Curie now began investigating the chemical element uranium.

Why Uranium?

In 1895, Wilhelm Roentgen had discovered mysterious X-rays, which could capture photographs of human bones beneath skin and muscle.

The following year, Henri Becquerel had discovered that rays emitted by uranium could pass through metal, but Becquerel’s rays were not X-rays.

Marie decided to investigate the rays from uranium – this was a new and very exciting field to work in. Discoveries came to her thick and fast. She discovered that:

• Uranium rays electrically charge the air they pass through. Such air can conduct electricity. Marie detected this using an electrometer Pierre and his brother invented.
• The number of rays coming from uranium depends only on the amount of uranium present – not the chemical form of the uranium. From this she theorized correctly that the rays came from within the uranium atoms and not from a chemical reaction.
• The uranium minerals pitchblende and torbernite have more of an effect on the conductivity of air than pure uranium does. She theorized correctly that these minerals must contain another chemical element, more active than uranium.
• The chemical element thorium emits rays in the same way as uranium. (Gerhard Carl Schmidt in Germany actually discovered this a few weeks before Marie Curie in 1898: she discovered it independently.)

By the summer of 1898, Marie’s husband Pierre had become as excited about her discoveries as Marie herself. He asked Marie if he could cooperate with her scientifically, and she welcomed him. By this time, they had a one-year old daughter Irene. Amazingly, 37 years later, Irene Curie herself would win the Nobel Prize in Chemistry.

Discovery of Polonium and Radium, and Coining a New Word

Marie and Pierre decided to hunt for the new element they suspected might be present in pitchblende. By the end of 1898, after laboriously processing tons of pitchblende, they announced the discovery of two new chemical elements which would soon take their place in Dmitri Mendeleev’s periodic table.

The first element they discovered was polonium, named by Marie to honor her homeland. They found polonium was 300 times more radioactive that uranium. They wrote:

“We thus believe that the substance that we have extracted from pitchblende contains a metal never known before, akin to bismuth in its analytic properties. If the existence of this new metal is confirmed, we suggest that it should be called polonium after the name of the country of origin of one of us.”

The second element the couple discovered was radium, which they named after the Latin word for ray. The Curies found radium is several million times more radioactive than uranium! They also found radium’s compounds are luminous and that radium is a source of heat, which it produces continuously without any chemical reaction taking place. Radium is always hotter than its surroundings.

Together they came up with a new word for the phenomenon they were observing: radioactivity. Radioactivity is produced by radioactive elements such as uranium, thorium, polonium and radium.

A Ph.D. and a Nobel Prize in Physics!

In June 1903, Marie Curie was awarded her Ph.D. by the Sorbonne.

Her examiners were of the view that she had made the greatest contribution to science ever found in a Ph.D. thesis.

Six months later, the newly qualified researcher was awarded the Nobel Prize in Physics!

She shared the prize with Pierre Curie and Henri Becquerel, the original discover of radioactivity.

The Nobel Committee were at first only going to give prizes to Pierre Curie and Henri Becquerel.

However, Pierre insisted that Marie must be honored.

So three people shared the prize for discoveries in the scientific field of radiation.

Marie Curie was the first woman to be awarded a Nobel Prize.

 

Amedeo Avogadro

                                 Lived 1776 – 1856.

Amedeo Avogadro is best known for his hypothesis that equal volumes of different gases contain an equal number of molecules, provided they are at the same temperature and pressure.

His hypothesis was rejected by other scientists. It only gained acceptance after his death. It is now called Avogadro’s law.

Avogadro was also the first scientist to realize that elements could exist in the form of molecules rather than as individual atoms.

Avogadro’s Life

Amedeo Avogadro was born in Turin, Italy, on August 9th, 1776.

His family background was aristocratic. His father, Filippo, was a magistrate and senator who had the title of Count. His mother was a noblewoman, Anna Vercellone of Biella.

Amedeo Avogadro inherited the title of Count from his father. In fact, Amedeo Avogadro’s full name was Count Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto – quite a mouthful!

Avogadro was highly intelligent. In 1796, when he was only 20, he was awarded a doctorate in canon law and began to practice as an ecclesiastical lawyer.

Although he had followed the family tradition by studying law, he gradually lost interest in legal matters. He found science was much more intellectually stimulating.

Mathematics and physics in particular attracted his logical mind. He spent increasing amounts of time studying these subjects. He was helped in this by the prominent mathematical physicist Professor Vassalli Eandi.

In 1803, in cooperation with his brother Felice, Avogadro published his first scientific paper, which looked at the electrical behavior of salt solutions. This was state-of-the-art science: only three years earlier, Avogadro’s fellow Italian Alessandro Volta had invented the electric battery.

In 1806, aged 30, Avogadro abandoned his successful legal practice and started teaching mathematics and physics at a high school in Turin. In 1809 he became a senior teacher at the College of Vercelli.

In 1820 Avogadro became professor of mathematical physics at the University of Turin. Unfortunately, this post was short lived because of political turmoil. Avogadro lost his job in 1823.

Avogadro was reappointed in 1833 and remained in this post until, at the age of 74, he retired in 1850.

Although he was an aristocrat, Avogadro was a down-to-earth, private man, who was quietly religious. He worked hard and his lifestyle was simple. His wife’s name was Felicita Mazzé. They married in 1818 when Avogadro was aged 42. They had six sons.

Avogadro’s Contributions to Science

In the early 1800s, scientists’ ideas about the particles we now call atoms and molecules were very limited and often incorrect. Avogadro was deeply interested in finding out how the basic particles of matter behave and come together to form chemical compounds.

He studied the work of two other scientists:

1. John Dalton
In 1808 John Dalton published his atomic theory proposing that all matter is made of atoms. He further stated that all atoms of an element are identical, and the atoms of different elements have different masses. In doing so, Dalton carried chemistry to a new level. But he also made mistakes about the way elements combine to form compounds. For example, he thought water was made of one hydrogen atom and one oxygen atom and wrote it as HO; today we know water contains two hydrogens to every oxygen and we write water as H20. Actually, Avogadro figured this out, as we shall see.

2. Joseph Gay-Lussac
In 1809 Joseph Gay-Lussac published his law of combining gas volumes. He had noticed that when two liters of hydrogen gas react with one liter of oxygen gas, they form two liters of gaseous water. All gases that he reacted seemed to react in simple volume ratios.

Avogadro’s Hypothesis

In 1811 Avogadro published a paper in Journal de Physique, the French Journal of Physics. He said that the best explanation for Gay-Lussac’s observations of gas reactions was that equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules. This is now called Avogadro’s law. He published it when he was working as a physics teacher at the College of Vercelli.

In Avogadro’s (correct) view, the reason that two liters of hydrogen gas react with a liter of oxygen gas to form just two liters of gaseous water is that the volume decreases because the number of particles present decreases. Therefore the chemical reaction must be:

2H2 (gas) + O2 (gas) → 2H20 (gas)

In this reaction three particles (two hydrogen molecules and one oxygen molecule) come together to form two particles of water… or 200 particles react with 100 particles to form 200 particles… or 2 million particles react with 1 million particles to form 2 million particles… etc. The observable effect is that after the reaction, when all of the hydrogen and oxygen gases have become H20 gas, the volume of gas falls to two-thirds of the starting volume.

As a result of these observations Avogadro became the first scientist to realize that elements could exist as molecules rather than as individual atoms. For example, he recognized that the oxygen around us exists as a molecule in which two atoms of oxygen are linked.

 

André Marie Ampère

Lived 1775 – 1836.

André-Marie Ampère made the revolutionary discovery that a wire carrying electric current can attract or repel another wire next to it that’s also carrying electric current. The attraction is magnetic, but no magnets are necessary for the effect to be seen. He went on to formulate Ampere’s Law of electromagnetism and produced the best definition of electric current of his time.

Ampère also proposed the existence of a particle we now recognize as the electron, discovered the chemical element fluorine, and grouped elements by their properties over half a century before Dmitri Mendeleev produced his periodic table.

The SI unit of electric current, the ampere, is named in his honor.

Beginnings

André-Marie Ampère was born into a well-to-do family in the city of Lyon, France, on January 20, 1775. His father was Jean-Jacques Ampère, a businessman; his mother was Jeanne Antoinette Desutières-Sarcey, the orphaned daughter of a silk-merchant. André-Marie’s parents already had a daughter, Antoinette, born two years before André-Marie.

It was an intellectually exciting period in French history; Antoine Lavoisier was revolutionizing chemistry; and Voltaire and Jean-Jacques Rousseau, the leaders of the French Enlightenment, were urging that society should be founded on science, logic, and reason rather than the religious teachings of the Catholic Church.

When André-Marie was five years old, his family moved to a country estate near the village of Poleymieux about six miles (10 km) from Lyon. His father had grown so wealthy that he no longer needed to spend much time in the city. A second daughter Josephine was born when André-Marie was eight.

An Unusual Education
The education André-Marie received was rather unusual. His father was a great admirer of Jean-Jacques Rousseau, one of the leaders of the French Enlightenment. He decided to follow Rousseau’s approach for André-Marie’s education. This meant no formal lessons.

André-Marie could do as he pleased, learning about anything he felt like. He was also allowed to read anything he wanted to from his father’s large library. A recipe for disaster, you may think? In fact, it worked! And it worked exceptionally well. André-Marie developed an insatiable thirst for knowledge, going as far as learning entire pages of an encyclopedia by heart.

Although a child of the French Enlightenment, André-Marie did not reject the church, and he remained a practicing Catholic throughout his life.

“My father… never required me to study anything, but he knew how to inspire in me a great desire for knowledge. Before learning to read, my greatest pleasure was to listen to passages from Buffon’s natural history. I constantly requested him to read me the history of animals and birds…”

 

Mathematics
Aged 13, André-Marie began a serious study of mathematics using books in his father’s library. He submitted a paper about conic sections to the Academy of Lyon, but it was rejected.

The rejection spurred him into working harder than ever. His father bought him specialist books to help him improve. He also took his son into Lyon, where Abbot Daburon gave him lessons in calculus – the first formal lessons André-Marie ever had.

Physics
Having taken his son for formal mathematics lessons, his father also took him to Lyon’s college to attend some physics lectures, which resulted in André-Marie beginning to read physics books as well as mathematics books.

Revolution Followed by Tragedies
Life so far had been peaceful and enjoyable for André-Marie, but a period of tragedy was beginning to unfold.

In 1789, when André-Marie was 14, the French Revolution began.

In 1791, while André-Marie continued his home-studies on their country estate, the revolutionaries gave his father the legal role of Justice of the Peace.

In 1792, André-Marie’s older sister Antoinette died.

In 1793, the Jacobin faction of the revolution guillotined his father. (The great chemist Antoine Lavoisier was guillotined by revolutionaries in 1794.)

Mercifully, André-Marie, studying mathematics and science on the family estate, survived the revolution’s reign of terror. He was devastated by his father’s death and abandoned his studies for a year.

Becoming a Mathematician and Scientist

In late 1797, aged 22, André-Marie Ampère opened up shop as a private mathematics tutor in Lyon. He proved to be an excellent tutor, and soon students were flocking to him for help.

His tutoring work came to the attention of Lyon’s intellectuals, who were impressed by Ampère’s knowledge and his enthusiasm.

In 1802, he became a school teacher in the town of Bourg 40 miles (60 km) from Lyon. A year later he returned to Lyon to work in another teaching position.

In 1804, he moved to the French capital, Paris, tutoring university level classes at the École Polytechnique. His work impressed other mathematicians so much that he was promoted to full professor of mathematics in 1809, despite having no formal qualifications.

André-Marie Ampère’s Contributions to Science

Electromagnetism and Electrodynamics

In 1800, while Ampère worked as a private tutor in Lyon, Alessandro Volta had invented the electric battery. One result of this was that for the first time ever, scientists could produce a steady electric current.

In April 1820, Hans Christian Oersted discovered that a flow of electric current in a wire could deflect a nearby magnetic compass needle. Oersted had discovered a link between electricity and magnetism – electromagnetism.

In September 1820, François Arago demonstrated Oersted’s electromagnetic effect to France’s scientific elite at the French Academy in Paris. Ampère was present, having been elected to the Academy in 1814.

Ampère was fascinated by Oersted’s discovery and decided he would try to understand why electric current produced a magnetic effect.

The Electron

To explain the relationship between electricity and magnetism, Ampère proposed the existence of a new particle responsible for both of these phenomena – the electrodynamic molecule, a microscopic charged particle we can think of as a prototype of the electron. Ampère correctly believed that huge numbers of these electrodynamic molecules were moving in electric conductors, causing electric and magnetic phenomena.

Discovery of Fluorine

Ampère did not restrict his interests to mathematics and physics; they were wide ranging and included philosophy and astronomy. He was particularly interested in chemistry. In fact, preceding his work in electromagnetism, he made significant contributions to chemistry.

Ampère discovered and named the element fluorine. In 1810, he proposed that the compound we now call hydrogen fluoride consisted of hydrogen and a new element: the new element had similar properties to chlorine he said. He and Humphry Davy, who was British, entered into correspondence (even though France and Britain were at war). Ampère proposed that fluorine could be isolated by electrolysis, which Davy had previously used to discover elements such as sodium and potassium.

It was only in 1886 that French chemist Henri Moissan finally isolated fluorine. He achieved this using electrolysis, the method Ampère had recommended.