Thread by @realscientists

Hey all, let us have a look at some basics of optics and light science today! #phdchat #Physics #optics

Let us look at some common objects that can be used to understand the nature of light rays. This includes mirrors and lenses. #phdchat #physics #optics

Light travels in a straight line. It is the most fundamental property of light. An obstruction on the path may only change its direction, else it travels in a straight line. #phdchat #optics #light

Back to the objects used to study the nature of light.
Lenses: When light falls onto a lens, the light from top of the object will be refracted to the bottom and light from the bottom will be refracted to the top. This is true for a convex lens. #phdchat #lens #optics

That means, when we view an object through a convex lens, it will look inverted! This is a picture of my lab door as seen though a convex lens. #optics #physics #phdchat

Sorry about the break. Back to the basics of optics now! Here is a tiny fact about lenses. The first lens was not a solid piece of glass. Roman philosopher Seneca observed that a bowl of water could magnify objects. #histSTM #optics #physics #phdchat

Later in 1250, Roger Bacon invented the first convex lens. #histSTEM #PhDChat #optics

The word lens is derived from the Latin word 'lentil' and it means transparent mirror. Initially glass balls (lenses) were used as accessories and for religious purposes but these lenses have become ubiquitous today. #histSTM #physics #optics #PhDChat

One of the most prominent use of a convex lens dares back to the 12th or 13th century. During this time, it was used as a simple magnifier to read small letters. These magnifiers were referred to as devil's tools!

Following this, the eyeglasses emerged to fix problem with the eyesight. Following that we had robust instruments which gave science a whole new perspective! #optics #physics #optics #histSTEM

We have microscopes to delve deeper into the tiny kingdom not otherwise visible to the naked eye. #microscopes #optics #histSTEM

And we have telescope, to take us into the far alleys of the universe! #histSTEM #physics #optics

The next important and fundamental object which revolutionized the laws of optics is a mirror. A simple mirror. #histSTEM #physics #optics #phdchat

The first mirror was made by Rimand and Egyptians by polishing copper and bronze! #histSTEM #physics #optics #phdchat

Later, glass was made by polishing glass with reflective chemicals. #histSTEM #optics #physics

The main reason why a glass gets coated is because of the poor reflective nature of glass. If it isn't costed, we can just see through it! #phdchat #optics #histSTEM

Until 1835, mirrors were considered to be a luxury owning to the tedious process involved in making it. Saint Gobain in France was the lead manufacturers of mirrors for the rich. #histSTM #physics #optics

Mirrors work much different from how a lens works! They do not produce inverted images like a lens does. #optics #physics #PhDchat

I forgot to mention a point. Mirrors and lenses can be either convex or concave depending on how they are curved. #phdchat #optics #physics

A simple example of a system consisting of both a convex and a concave mirror is a spoon. Yes, a simple tea steel spoon! The inner side of the spoon, the one which holds the food, acts like a concave mirror and the backside acts as a convex mirror #optics #phdchat #basics

The next things about light is that, white light is made of three primary colors - red, green, and blue. Every other colored light out there is a combination of these three colors. #phdchat #optics #physics

Here is a simple experiment that I did to demonstrate that. I have used red, blue, and green LEDs and a white screen. #optics #physics #PhDchat

And white light is just a small part of the visible spectrum. The spectra is much wider. We have X rays, Gamma rays, ultraviolet rays, infrared rays, microwaves, and radio waves. While they are all light, their wavelengths and frequencies vary over a large range. #phdchat #optics

The visible spectrum, as the name suggests, is visible to the naked eye. Its colours are the colours of the rainbow. But there are other raditaions/light that are invisible though they are present all around us. #phdchat #optics #physics

Take mid infrared radiation. They have larger wavelength than that of visible light. Our bodies emit infrared radiation at all times. #optics #physics #phdchat

Here is another small experiment that I did to show you this invisible radiation. I use a black film which changes its colour to green and then blue on exposure to mid infra-red radiation. See what happens when I place it over the palm. #optics #physics #phdchat

Every range of the light spectrum comes with it's own advantages. #phdchat #optics #light

But do we have to potential to take energy from one regime in the spectrum and send it to another regime? Yeah, why not! That's where the term fluorescence comes in. #phdchat #optics #photonics

Take a simple neon marker. The ink used in such a marker are fluorescent in nature. When ultraviolet light falls on the ink, the electrons from lower energy levels can jump into higher energy levels. On decaying back, they emit light in the visible regime. Tada! #optics #phdchat

Here, I have used a fluorescent ink to write a message on a black chart and as you can see, it is invisible when seen with naked eye with a bit of sunlight. Then I turn on a ultraviolet LED. See, what message I have for you! #optics #phdchat #light

Another important point about light is that it can behave as both wave and a particle :) Another counterintuitive idea but quite interesting! #phdchat #optics #light

You can imagine this as follows. Everytime a particle is dropped into a pool of water, a ripple forms. So now to understand the disturbance created in the medium, we can look at the stone itself or the ripple that's formed. #phdchat #optics #light

Some phenomena can be explained using wave nature and some using particle nature. #phdchat #optics #light

These are some fundamental features of light. To conclude this thread, I want to show you what's called a Pepper Ghost! #phdchat #optics #light

Using this effect, you can easily create a 3D projection, right from your home. All you need is a sheet of plastic and YouTube! #phdchat #optics #hologram

Take a sheet of plastic, crease and cut as shown, fold it and place over your mobile phone/tablet. Go to YouTube, search for a Peppergram video ( should look like a kaleidoscopic video) and play it in fullscreen. View not from the top but from one side. #phdchat #optics

The entire effect is just due to refraction at the different faces of the plastic structure. The light from the screen changes direction and finally falls into the centre to create a 3D like image. #phdchat #optics #light

Here is another simple demonstration of how a set of lenses could be used to make an object invisible! This is again due to the way light gets refracted out from the point of view of the observer. #optics #light #phdchat

A lot of applications which were introduced to the world as part of science fiction took life with advances in optics. Some prominent examples include bluetooth and the invisibility cloak! #phdchat #optics #physics #fun

With this, I close this thread. More fun optics stuff at @sivashakthi!