Light is all around us, making our world an easy place to navigate. But, what really is light? And why does it behave the way it does. It's a question that has spurred the curiosity of ancient Greek philosophers like Epicurus to the modern day scientists working at CERN.
At the basic level light is described as ___________
Light is an electromagnetic radiation. But what does that mean? Electromagnetic Radiation is one of the ways energy is transmitted - in the form of a wave. Electro magnetic wave is made up of two fields, an electric field and a magnetic field that swing back and forth at 90 degrees to one another in a synchronised manner. But, here is an interesting thing. Light is a not just a radiation wave; it is also a particle.
The light particles are known as ___________
Photons are tiny bundles of electromagnetic energy that make up light. Hence it is described as a particle (smallest unit of matter that occupies space and has mass). But, photons don't have mass and are always in motion. Here is where light gets weird and a little difficult to understand. It has a dual personality - it can be a wave or a particle but not both at the same time.
All the elements in the universe are made up of a small unit called an atom. The atom can be further broken down into protons, neutrons and electrons. The electrons revolves around the nucleus (center of the atom that contains neutrons and protons) in orbits. When an atom absorbs energy, the electron move higher up the orbit. This is known as an excited state and electrons don't like to stay excited very long. So, to jump back to their original stable state, they emit a photon or one bundle of electro-magnetic energy called light.
Visible Light - is small part of the electromagnetic radiation range. The range is based on the wavelength - the distance between two successive peaks or valleys in a wave.
The longest wavelength in the visible spectrum belongs to the colour _________
Visible spectrum is composed of VIBGYOR (Rainbow Colors); Violet, Indigo, Blue, Green, Yellow, Orange and Red. Red has the longest wavelength while violet has the shortest.
Isaac Newton was the first scientist to discover the visible spectrum. He found out that when light passes through a prism, different components of light break up and change direction revealing a spectrum of color.
This is known as __________
When a narrow beam of light strikes a Prism at an angle, the light waves changes speed and direction as it enters and leaves the prism. In vacuum or space, all the colors in the visible spectrum travel at the same speed, but in the prism the speed and the amount of bend differs for different colors. Higher the speed, larger the bend. The color red which has the lowest speed bends the least, while violet with the highest speed bends the most. This leads to dispersion of light.
We talked about light bending when it enters and leaves the prism. When a light enters from one medium into another, it changes direction. In the image, bending of light creates an illusion of broken pencil.
This is phenomenon called __________?
Though it may not seem like much, refraction has very important every day use. Corrective lenses like spectacles and contact lenses work on the principle of refraction. So do Fiber optic cables, microscope, telescope etc. And most importantly our eyes can see because of the refraction of light by cornea on to the retina - which helps us see all the color of the nature.
But, how does an object gets it's color?
The colour of an object is mainly determined by the wavelength(s) _________ by the object
The colour that we see is the wavelength(s) or the color that is reflected by the object. The objects that absorbs all wavelength are visible to us as 'black' and the ones that reflect back all wavelengths appear as 'white' . This is the reason black tends to heat up faster as it absorbs all the wavelengths. Most of the electromagnetic radiation do not reach the earth except for partial UV, visible, partial IR and radio waves. Over the years, the human eyes have evolved to see only that part of electromagnetic spectrum which we call the visible wavelengths of light.
The part of the eyes that is sensitive to different wavelength is?
Cone cells are a part of Retina that are sensitive to bright light and can distinguish the different wavelengths. When a certain wavelength of visible light enters the cone, a chemical reaction takes place resulting in an electric impulse that is signaled to the brain which in turn interprets the colour.
What is the speed of light in vaccum?
The speed of the light varies according to the medium it travles in-- but the constant value used for all the calculations is the speed of light in a vacuum denoted by "c", which is equal to exactly 299,792,458 metres per second. It was in 1983, that the exact value of speed of light was known.
Light may travel the fastest, but here is a fun fact, when we look up at the night sky, we might be seeing the stars that are already dead a long time ago. They might have died even before you were born. We can see them now because these stars are so far away that it takes hundreds of lights years for their light to reach us. Because light travels at such high speeds they are used as measures of astronomical distance.
What is a light year?
The distance that light travels in one year-- Light year is equal to the distance it takes the light to travel in a year. This value is 9.4607 × 1012 km.
The farthest visible star is 16,308 light-years away from us. The amount of time it approximately takes for the sunlight to reach the earth is just 8.3 minutes.
Visible light is the reason we can differentiate textures, gauge the depth and distance our surrounding. Though just a sliver of the electro-magnetic radiation, it has shaped our lives on this planet innumerable ways. It also continues to fascinate us with the opportunities it provides to explore and further the reaches of science.
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