Presentation on theme: "The Masters of Light – a history of the celebrities of light from Euclid to Einstein – a history of the celebrities of light from Euclid to Einstein."— Presentation transcript:
The Masters of Light – a history of the celebrities of light from Euclid to Einstein – a history of the celebrities of light from Euclid to Einstein
The beginning and Big Bang The beginning and Big Bang Euclid – the law of reflection Euclid – the law of reflection Alhazen – the origin of light Alhazen – the origin of light Snell & Descartes – the law of refraction Snell & Descartes – the law of refraction Fermat´s principle Fermat´s principle Ole Rømer – the hesitation of light Ole Rømer – the hesitation of light Newton – the spectrum of light Newton – the spectrum of light Huygens principle Huygens principle Young´s experiment Young´s experiment Maxwell – the electromagnetic waves Maxwell – the electromagnetic waves Bohr´s atomic model Bohr´s atomic model Einstein and light Einstein and light
The Beginning In the beginning God created the heavens and the earth. Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters. And God said, "Let there be light," and there was light. God saw that the light was good, and He separated the light from the darkness. God called the light "day," and the darkness he called "night." And there was evening, and there was morning — the first day. This is how Genesis begins. This is how Genesis begins.
Religion or science Genesis tells the story of creation which takes place upon seven days. But you cannot find the word “day” in the Hebrew manuscript. Instead of “day” the term “period” ought to be used. “Period” would be a more correct translation. Thus there is no conflict between religion and science at this point. The Big Bang took place about 14,000,000,000 years ago. It took about 300,000 years to cool the Universe sufficiently and to weaken the gravitational forces enough to make light escape. So from the beginning there was no light – only darkness, just as Genesis tells us. Consequently we will never be able to see the beginning of everything – without the light we are blind.
Euclid – the law of reflection The Greek philosophers made the first thoughts about the nature of the light. In the year 280 B.C. Euclid discovered that the light is spreading in an upright way and thus he formulated the law of reflection : The incident and the reflected ray of light are equal to the normal of the mirror and the angle of incidence is equal to the angle of reflection. But Euclid thought that light are rays which come from the eye. It had to spread with an infinite velocity as, when opening your eyes, you are immediately able to see distant objects. In the year 60 A. D. Heron of Alexandria advanced the general hypothesis that light is spreading according to the shortest distance between two points. On this basis he was able to derive the results of Euclid.
Alhazen – the origin of light About the year 1000 the focus of science had moved to the Arabic world, where Alhazen in Baghdad wrote a series of books about optics. Alhazen was the first to understand that light has its origin outside the human being and that the rays of light are reflected into the eyes from the objects they strike. Alhazen also advanced a hypothesis about the final velocity of light and the reduced velocity of light when passing through dense materials. Alhazen = Abu Ali Hasan Ibn Al-Haitham
Snell & Descartes – the law of refraction In 1621 the next major breakthrough took place. The Dutchman Willebrord Snell discovered how light is refracted by various materials. This is the law of refraction as demonstrated on the following page. René Descartes also formulated the Law of refraction, but he believed that light spreads with an infinite velocity.
The law of refraction. You can change the indices of refraction, view the rays of light and move the fish.
Fermat´s principle The Frenchman Pierre de Fermat did not agree with the theories of Descartes. He thought, just like Heron and Alhazen, that the light has a finite velocity. In 1657 he formulated the principle saying that light follows the shortest distance between 2 points. On this basis Fermat was able to formulate the law of the rectilinear spreading of light, the law of relection and the law of refraction which together form the basis of geometrical optics.
Ole Rømer – the hesitation of light In 1676 Ole Roemer performed a series of measurements of the periods of revolution for the moons of Jupiter. He observed irregularities in the periods of revolution. His explanation was the hesitation of light due to the variable distance between the Earth and Jupiter. Ole Roemer discovered that it takes the light 8 to 11 minutes to reach the Earth from the Sun. Today we know that it takes 8 minutes and 20 seconds. The velocity of light is m/s in vacuum, but normally we use the rounded figure km/s.
Newton – the spectrum of light In the sixteenth century Isaac Newton was the great master of mechanical physics. He also made important works of optics. He invented the reflecting telescope and discovered that the white light is formed by blending light of all colours. In 1704 Newton published his work ”Opticks – or a treatise of the reflexions, refractions, inflexions and colours of light”. Newton strongly advocated that light is made of particles.
Huygens´ principle The Dutch physicist Christiaan Huygens was an opponent of the ideas of light particles of Newton. In 1678 he published ”Traité de la Lumière”, where he described the nature of light as waves. The principle of Huygens states that each point of a ray of light can be explained by small waves coalesce to form a wave front. The theory of Huygens gave a beautiful explanation of refraction, diffraction, interference and reflection – and prepared the way for an interpretation of the polarization of the light and double refraction.
Young's experiment In 1801 the British doctor Thomas Young performed a conclusive experiment. He proved that light displays interference which is a single-valued wave length phenomenon. He decided this wave length to be about 0, 0005 mm. It was now possible to prove that all geometrical optics is a consequence of the wave theory.
Young´s experiment – interference between 2 sources of light (S 1 and S 2 ) Press ”Fringes” to view the screen. Move P to see the interference spectrum.
Maxwell – the electromagnetic waves James Clerk Maxwell became the first to investigate the relation between light and electromagnetic waves. The equations of Maxwell are an outstanding theoretical work based on the works of Faraday, Reimann and Gauss. In 1862 Maxwell wrote “hardly can we not avoid the conclusion that the light is made of transverse waves in the same medium which cause electric and magnetic phenomena.” Subsequently Hertz was the first to prove the theories of Maxwell experimentally by means of an oscilloscope.
Maxwell – the electromagnetic waves ( E=electric field, B=magnetic field ). You may change the frequency and the wave length.
Bohr´s atomic model Niels Henrik David Bohr is the most famous Dane next to H.C. Andersen. In 1913 he advanced the theory of his atomic model which indicates, that the electrons follow certain orbits around the nucleus. His theory implicates that there are a certain number of energy states for a an atom. Bohr´s theory explains a number of nuclear light phenomena. The complementary principle of Bohr implies that you may view light as waves or as particles – photons – depending on which phenomenon you consider. The correspondence principle of Bohr bridged the classic physics and the quantum physics.
Einstein and light In 1905 Albert Einstein described the light as packets of energy – photons. Different light have different photons and some photons are able to loosen electrons from certain metals. If the photons loosen a lot of electrons so that they succeed one another the electrons produce electricity. Thus Einstein explained the photoelectric effect. In 1917 Einstein developed the theory which resulted in the development of laser light. Watch the animation of photons.
The Moon reflects some of the light particles – photons – which come from the Sun. Press mirrors and watch photons being reflected.