Why is light waves
In a physicist in England, Thomas Young, performed an experiment that showed that light behaves as a wave. He passed a beam of light through two thin, parallel slits. Alternating bright and dark bands appeared on a white screen some distance from the slit. Young reasoned that if light were made of particles as Newton suggested, only two bright bands of light would be projected on the white surface. The bright and dark bands demonstrated that the slits were causing light waves to interfere with each other.
Sometimes this interference is constructive, and the light waves add together to create a bright patch. Sometimes the intereference is destructive and results in the light waves cancelling each other out creating dark patches on the screen. In , Italian physicist Francesco Maria Grimaldi to discovered the phenomenon of light diffraction and pointed out that it resembles the behavior of waves.
Then, in , Dutch physicist Christian Huygens to established the wave theory of light and announced the Huygens' principle. Some years after the time of Newton, French physicist Augustin-Jean Fresnel to asserted that light waves have an extremely short wavelength and mathematically proved light interference.
In , he devised physical laws for light reflection and refraction, as well. He also hypothesized that space is filled with a medium known as ether because waves need something that can transmit them.
At that point, the particle theory of light fell out of favor and was replaced by the wave theory. The next theory was provided by the brilliant Scottish physicist James Clerk Maxwell to In , he predicted the existence of electromagnetic waves, the existence of which had not been confirmed before that time, and out of his prediction came the concept of light being a wave, or more specifically, a type of electromagnetic wave.
Until that time, the magnetic field produced by magnets and electric currents and the electric field generated between two parallel metal plates connected to a charged capacitor were considered to be unrelated to one another. Maxwell changed this thinking when, in , he presented Maxwell's equations: four equations for electromagnetic theory that shows magnetic fields and electric fields are inextricably linked.
This led to the introduction of the concept of electromagnetic waves other than visible light into light research, which had previously focused only on visible light. The term electromagnetic wave tends to bring to mind the waves emitted from cellular telephones, but electromagnetic waves are actually waves produced by electricity and magnetism. Electromagnetic waves always occur wherever electricity is flowing or radio waves are flying about.
Maxwell's equations, which clearly revealed the existence of such electromagnetic waves, were announced in , becoming the most fundamental law of electromagnetics. These equations are not easy to understand, but let's take an in-depth look because they concern the true nature of light.
Maxwell's four equations have become the most fundamental law in electromagnetics. The first equation formulates Faraday's Law of Electromagnetic Induction, which states that changing magnetic fields generate electrical fields, producing electrical current.
The second equation is called the Ampere-Maxwell Law. It adds to Ampere's Law, which states an electric current flowing over a wire produces a magnetic field around itself, and another law that says a changing magnetic field also gives rise to a property similar to an electric current a displacement current , and this too creates a magnetic field around itself. The term displacement current actually is a crucial point.
The third equation is the law stating there is an electric charge at the source of an electric field. The fourth equation is Gauss's Law of magnetic field, stating a magnetic field has no source magnetic monopole equivalent to that of an electric charge. If you take two parallel metal plates electrodes and connect one to the positive pole and the other to the negative pole of a battery, you will create a capacitor.
Direct-current DC electricity will simply collect between the two metal plates, and no current will flow between them. However, if you connect alternating current AC that changes drastically, electric current will start to flow along the two electrodes.
Electric current is a flow of electrons, but between these two electrodes there is nothing but space, and thus electrons do not flow. Maxell wondered what this could mean. Then it came to him that applying an AC voltage to the electrodes generates a changing electric field in the space between them, and this changing electric field acts as a changing electric current.
This electric current is what we mean when we use the term displacement current. A most unexpected conclusion can be drawn from the idea of a displacement current. In short, electromagnetic waves can exist. This also led to the discovery that in space there are not only objects that we can see with our eyes, but also intangible fields that we cannot see.
The existence of fields was revealed for the first time. Solving Maxwell's equations reveals the wave equation, and the solution for that equation results in a wave system in which electric fields and magnetic fields give rise to each other while traveling through space. The form of electromagnetic waves was expressed in a mathematical formula. Magnetic fields and electric fields are inextricably linked, and there is also an entity called an electromagnetic field that is solely responsible for bringing them into existence.
The visible portion is a very small part of the electromagnetic spectrum. The distance is from the peak of one wave to the peak of the next. Humans can see wavelengths from about nm, which appears dark red, to about nm, which appears violet.
The light with short wavelengths violet carries more energy than the light with long wavelengths red. Image courtesy of Windows to the Universe In Sir Isaac Newton published a book called "Opticks" which explained some of the mysteries of light. Newton showed that sunlight is a mixture of a continuous spectrum of colors.