Our last series part 1:----[Revision Series] UPSC SSC (Part 1 of 8) Science
Our last series part 2:----[Revision Series] UPSC SSC (Part 2 of 8) Science
In first part, we covered the topic:--
1. Difference between scaler and vector quantity
2. The concept of densities important but you don’t need to mugup absolute density value of various substances. Same goes for surface tension, viscosity etc.
In second part, we covered the topics:-
1. The working principles behind artificial satellites, geostationary satellites etc.
2. The concept of densities important but you don’t need to mugup absolute density value of various substances.
Cover following topics for Physics:-
1. Difference between scaler and vector quantity
2. Newton’s laws and their practical application
3. The working principles behind artificial satellites, geostationary satellites etc.
4. The concept of densities important but you don’t need to mugup absolute density value of various substances. Same goes for surface tension, viscosity etc.
5. Concepts and principles behind heat, electronic thermometer, refrigeration, radiation, solar cooker, thermos flask, carengine radiator, air-conditioners, pressure cookers, DTH TV, night-vision goggles, radar, oven, CAT Scan etc.
6. Optics: convex and concave glasses: differences applications, refractions,
7. Principle behind rainbow, LCD, camera microscope, LASER, compact disc etc. but no need to get bored with those complex diagrams.
8. Sound: echo, resonsnace, doplar effect, sonic boom, dolby etc. : again you need to have idea on basics. No need for going into minute details.
9. Same for Magnetism and electricity, Nuclear physics.
10. In short, you should be aware of the concepts and principles but You don’t need to mugup equations of Velocity, acceleration, pendulum, sound etc.
Today in third part of [Revision Series] UPSC SSC (Part 3 of 8) Science, we will discuss:-
Principle behind rainbow, LCD, ordinary and digital camera, microscope, LASER, compact disc etc. but no need to get bored with those complex diagrams.
Principle behind rainbow
Figure 1:
Basic diagram showing formation of rainbow.
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'Overview
Note:
Angles not to scale.
The formation of a rainbow involves a series of physical phenomena - reflection, refraction, dispersion and total internal reflection.
The occurrence of each of these is due to the interaction of light with air and water and the boundaries between them.
The Steps Involved in the Process
Figure 2: Ray digram - light through raindrop
1. Light from Sun strikes raindrop
2. Some of the light is reflected
3. The rest of the light is refracted
4. Light splits into component colours
5. Reflected at rear of raindrop (TIR)
6. Refracted again as it leaves raindrop
7. Colours are further dispersed
1. Light from sun strikes raindrop.
White light from the Sun has to hit the raindrops at a certain angle before a rainbow is possible. It is best if the sun is fairly low in the sky such as dawn and late afternoon. The angle is important as it effect the direct the light travels after it hits the raindrops and that determines whether or not we will see a rainbow.
2. Some of the light is reflected.
It is possible to see through a glass window but, at the same time, see your own reflection. This is because the window both transmits and reflects light. Water can do this too - that is why you can see a reflection in a pool of clean water and also see the bottom.
When light from the sun hits a water droplet, some of the light is reflected. This light will obey the Law of Reflection.
3. The rest of the light is refracted.
The light that is not refracted crosses the air-water interface (boundary layer). When this happens it slows down because the water is more dense than the air. The reduction of speed cause the path of the light to bend - this is called refraction. In this case the path of the light rays bends toward the normal line.
4. White light splits into component colours.
White light is made up of a spectrum of colours, each with its own wavelength. Different wavelengths travel at different speeds and when they encounter a change to medium that is more dense or less dense, the speeds are efected by different amounts. Hence, the colours separate. This phenomenon is know as Dispersion.
5. Light is reflected at rear of raindrop (TIR).
At the rear of the raindrop, the light hits the water-to-air interface. If the angle of incidence is greater than the critical angle, Total Internal Reflection will occur. A rainbow will only be seen if this happens, otherwise the light will continue out the other side of the raindrop and continue to move away from the would-be viewer.
6. Light is refracted again as it leaves raindrop.
Just as the light changed speed as it entered the raindrop, its speed changes again as it leaves. Here, the light is moving from a more dense medium (water) to a less dense medium (air). As it does so, it speeds up and its path bends. In this case the path of the light rays bends away from the normal line. This is another example of refraction.
7. Colours are further dispersed.
As the rays are refracted once again, the various wavelengths are effected to different extents. The overall result of this is increased separation of the component colours of white light. This is Dispersion.
Principal behind LCDs (Liquid Crystal Displays)
Televisions used to be hot, heavy, power-hungry beasts that sat in the corner of your living room. Not any more! Now they're slim enough to hang on the wall and they use a fraction as much energy as they used to. Like laptop computers, most new televisions have flat screens with LCDs (liquid-crystal displays)—the same technology we've been using for years in things like calculators, cellphones, and digital watches. What are they and how do they work? Let's take a closer look!
How does a television screen make its picture?
For many people, the most attractive thing about LCD TVs is not the way they make a picture but their flat, compact screen. Unlike an old-style TV, an LCD screen is flat enough to hang on your wall. That's because it generates its picture in an entirely different way.
You probably know that an old-style cathode-ray tube (CRT) television makes a picture using three electron guns. Think of them as three very fast, very precise paintbrushes that dance back and forth, painting a moving image on the back of the screen that you can watch when you sit in front of it.
Flatscreen LCD and plasma screens work in a completely different way. If you sit up close to a flatscreen TV, you'll notice that the picture is made from millions of tiny blocks called pixels (picture elements). Each one of these is effectively a separate red, blue, or green light that can be switched on or off very rapidly to make the moving color picture. The pixels are controlled in completely different ways in plasma and LCD screens. In a plasma screen, each pixel is a tiny fluorescent lamp switched on or off electronically. In an LCD television, the pixels are switched on or off electronically using liquid crystals to rotate polarized light. That's not as complex as it sounds! To understand what's going on, first we need to understand what liquid crystals are; then we need to look more closely at light and how it travels.
What are liquid crystals?
We're used to the idea that a given substance can be in one of three states: solid, liquid, or gas—we call them states of matter—and up until the late 19th century, scientists thought that was the end of the story. Then, in 1888, an Austrian chemist named Friedrich Reinitzer (1857–1927) discovered liquid crystals, which are another state entirely, somewhere in between liquids and solids. Liquid crystals might have lingered in obscurity but for the fact that they turned out to have some very useful properties.
Solids are frozen lumps of matter that stay put all by themselves, often with their atoms packed in a neat, regular arrangement called a crystal (or crystalline lattice). Liquids lack the order of solids and, though they stay put if you keep them in a container, they flow relatively easily when you pour them out. Now imagine a substance with some of the order of a solid and some of the fluidity of a liquid. What you have is a liquid crystal—a kind of halfway house in between. At any given moment, liquid crystals can be in one of several possible "substates" (phases) somewhere in a limbo-land between solid and liquid. The two most important liquid crystal phases are called nematic and smectic:
1. When they're in the nematic phase, liquid crystals are a bit like a liquid: their molecules can move around and shuffle past one another, but they all point in broadly the same direction. They're a bit like matches in a matchbox: you can shake them and move them about but they all keep pointing the same way.
2. If you cool liquid crystals, they shift over to the smectic phase. Now the molecules form into layers that can slide past one another relatively easily. The molecules in a given layer can move about within it, but they can't and don't move into the other layers (a bit like people working for different companies on particular floors of an office block). There are actually several different smectic "subphases," but we won't go into them in any more detail here.
What is polarized light?
Nematic liquid crystals have a really neat party trick. They can adopt a twisted-up structure and, when you apply electricity to them, they straighten out again. That may not sound much of a trick, but it's the key to how LCD displays turn pixels on and off. To understand how liquid crystals can control pixels, we need to know about polarized light.
Light is a mysterious thing. Sometimes it behaves like a stream of particles—like a constant barrage of microscopic cannonballs carrying energy we can see, through the air, at extremely high speed. Other times, light behaves more like waves on the sea. Instead of water moving up and down, light is a wave pattern of electrical and magnetic energy vibrating through space.
When sunlight streams down from the sky, the light waves are all mixed up and vibrating in every possible direction. But if we put a filter in the way, with a grid of lines arranged vertically like the openings in prison bars (only much closer together), we can block out all the light waves except the ones vibrating vertically (the only light waves that can get through vertical bars). Since we block off much of the original sunlight, our filter effectively dims the light. This is how polarizing sunglasses work: they cut out all but the sunlight vibrating in one direction or plane. Light filtered in this way is called polarized or plane-polarized light (because it can travel in only one plane).
If you have two pairs of polarizing sunglasses (and it won't work with ordinary sunglasses), you can do a clever trick. If you put one pair directly in front of the other, you should still be able to see through. But if you slowly rotate one pair, and keep the other pair in the same place, you will see the light coming through gradually getting darker. When the two pairs of sunglasses are at 90 degrees to each other, you won't be able to see through them at all. The first pair of sunglasses blocks off all the light waves except ones vibrating vertically. The second pair of sunglasses works in exactly the same way as the first pair. If both pairs of glasses are pointing in the same direction, that's fine—light waves vibrating vertically can still get through both. But if we turn the second pair of glasses through 90 degrees, the light waves that made it through the first pair of glasses can no longer make it through the second pair. No light at all can get through two polarizing filters that are at 90 degrees to one another.
How LCD televisions use liquid crystals and polarized light
An LCD TV screen uses the sunglasses trick to switch its colored pixels on or off. At the back of the screen, there's a large bright light that shines out toward the viewer. In front of this, there are the millions of pixels, each one made up of smaller areas called sub-pixels that are colored red, blue, or green. Each pixel has a polarizing glass filter behind it and another one in front of it at 90 degrees. That means the pixel normally looks dark. In between the two polarizing filters there's a tiny twisted, nematic liquid crystal that can be switched on or off (twisted or untwisted) electronically. When it's switched on, it rotates the light passing through it through 90 degrees, effectively allowing light to flow through the two polarizing filters and making the pixel look bright. Each pixel is controlled by a separate transistor (a tiny electronic component) that can switch it on or off many times each second
How colored pixels in LCD TVs work
There's a bright light at the back of your TV; there are lots of colored squares flickering on and off at the front. What goes on in between? Here's how each colored pixel is switched on or off:
How pixels are switched off
1. Light travels from the back of the TV toward the front from a large bright light.
2. A horizontal polarizing filter in front of the light blocks out all light waves except those vibrating horizontally.
3. Only light waves vibrating horizontally can get through.
4. A transistor switches off this pixel by switching on the electricity flowing through its liquid crystal. That makes the crystal straighten out (so it's completely untwisted), and the light travels straight through it unchanged.
5. Light waves emerge from the liquid crystal still vibrating horizontally.
6. A vertical polarizing filter in front of the liquid crystal blocks out all light waves except those vibrating vertically. The horizontally vibrating light that travelled through the liquid crystal cannot get through the vertical filter.
7. No light reaches the screen at this point. In other words, this pixel is dark.
How pixels are switched on
1. The bright light at the back of the screen shines as before.
2. The horizontal polarizing filter in front of the light blocks out all light waves except those vibrating horizontally.
3. Only light waves vibrating horizontally can get through.
4. A transistor switches on this pixel by switching off the electricity flowing through its liquid crystal. That makes the crystal twist. The twisted crystal rotates light waves by 90° as they travel through it.
5. Light waves that entered the liquid crystal vibrating horizontally emerge from it vibrating vertically.
6. The vertical polarizing filter in front of the liquid crystal blocks out all light waves except those vibrating vertically. The vertically vibrating light that emerged from the liquid crystal can now get through the vertical filter.
7. The pixel is lit up. A red, blue, or green filter gives the pixel its color.
What's the difference between LCD and plasma?
A plasma screen looks similar to an LCD, but works in a completely different way: each pixel is effectively a microscopic fluorescent lamp glowing with plasma. A plasma is a very hot form of gas in which the atoms have blown apart to make negatively charged electrons and positively charged ions (atoms minus their electrons). These move about freely, producing a fuzzy glow of light whenever they collide. Plasma screens can be made much bigger than ordinary cathode-ray tube televisions, but they are also much more expensive.
Principle behind ordinary and digital camera
How ordinary film cameras work
If you have an old-style camera, you'll know that it's useless without one vital piece of equipment: a film. A film is a long spool of flexible plastic coated with special chemicals (based on compounds of silver) that are sensitive to light. To stop light spoiling the film, it is wrapped up inside a tough, light-proof plastic cylinder—the thing you put in your camera.
When you want to take a photograph with a film camera, you have to press a button. This operates a mechanism called the shutter, which makes a hole (the aperture) open briefly at the front of the camera, allowing light to enter through the lens (a thick piece of glass or plastic mounted on the front). The light causes reactions to take place in the chemicals on the film, thus storing the picture in front of you.
This isn't quite the end of the process, however. When the film is full, you have to take it to a drugstore (chemist's) to have it developed. Usually, this involves placing the film into a huge automated developing machine. The machine opens up the film container, pulls out the film, and dips it in various other chemicals to make your photos appear. This process turns the film into a series of "negative" pictures—ghostly reverse versions of what you actually saw. In a negative, the black areas look light and vice-versa and all the colors look weird too because the negative stores them as their opposites. Once the machine has made the negatives, it uses them to make prints (finished versions) of your photos.
If you want to take only one or two photographs, all of this can be a bit of a nuisance. Most people have found themselves wasting photographs simply to "finish off the film." Often, you have to wait several days for your film to be developed and your prints (the finished photographs) returned to you. It's no wonder that digital photography has become very popular—because it solves all these problems at a stroke.
How digital cameras work
Digital cameras look very much like ordinary film cameras but they work in a completely different way. When you press the button to take a photograph with a digital camera, an aperture opens at the front of the camera and light streams in through the lens. So far, it's just the same as a film camera. From this point on, however, everything is different. There is no film in a digital camera. Instead, there is a piece of electronic equipment that captures the incoming light rays and turns them into electrical signals. This light detector is called a charge-coupled device (CCD).
Photo: A typical CCD chip. The green rectangle in the center (about the size of a fingernail) is the light-sensitive part; the gold wires coming off it connect it into the camera circuit.
If you've ever looked at a television screen close up, you will have noticed that the picture is made up of millions of tiny colored dots or squares called pixels. Laptop LCD computer screens also make up their images using pixels, although they are often much too small to see. In a television or computer screen, electronic equipment switches all these colored pixels on and off very quickly. Light from the screen travels out to your eyes and your brain is fooled into see a large, moving picture.
In a digital camera, exactly the opposite happens. Light from the thing you are photographing zooms into the camera lens. This incoming "picture" hits the CCD, which breaks it up into millions of pixels. The CCD measures the color and brightness of each pixel and stores it as a number. Your digital photograph is effectively an enormously long string of numbers describing the exact details of each pixel it contains. You can read more about how a CCD produces a digital photograph in our article on webcams.
How digital cameras use digital technology
Once a picture is stored in numeric form, you can do all kinds of things with it. Plug your digital camera into your computer, and you can download the images you've taken and load them into programs like PhotoShop to edit them or jazz them up. Or you can upload them onto websites, email them to friends, and so on. This is possible because your photographs are stored in digital format and all kinds of other digital gadgets—everything from MP3-playing iPods to cellphones and computers to photo printers—use digital technology too. Digital is a kind of language that all electronic gadgets "speak" today.
Taking a digital photo: looking at the image on the LCD screen.
If you open up a digital photograph in a paint (image editing) program, you can change it in all kinds of ways. A program like this works by adjusting the numbers that represent each pixel of the image. So, if you click on a control that makes the image 20 percent brighter, the program goes through all the numbers for each pixel in turn and increases them by 20 percent. If you mirror an image (flip it horizontally), the program reverses the sequence of the numbers it stores so they run in the opposite direction. What you see on the screen is the image changing as you edit or manipulate it. But what you don't see is the paint program changing all the numbers in the background.
Some of these image-editing techniques are built into more sophisticated digital cameras. You might have a camera that has an optical zoom and a digital zoom. An optical zoom means that the lens moves in and out to make the incoming image bigger or smaller when it hits the CCD. A digital zoom means that the microchip inside the camera blows up the incoming image without actually moving the lens. So, just like moving closer to a TV set, the image degrades in quality. In short, optical zooms make images bigger and just as clear, but digital zooms make images bigger and more blurred.
Why digital cameras compress images
mage for a moment that you're a CCD. Look out of a window and try to figure out how you would store details of the view you can see. First, you'd have to divide the image into a grid of squares. So you'd need to draw an imaginary grid on top of the window. Next, you'd have to measure the color and brightness of each pixel in the grid. Finally, you'd have to write all these measurements down as numbers. If you measured the color and brightness for six million pixels and wrote both down both things as numbers, you'd end up with a string of millions of numbers—just to store one photograph! This is why high-quality digital images often make enormous files on your computer. Each one can be several megabytes (millions of characters) in size.
To get around this, digital cameras, computers, and other digital gadgets use a technique called compression. Compression is a mathematical trick that involves squeezing digital photos so they can be stored with fewer numbers and less memory. One popular form of compression is called JPG (pronounced J-PEG, which stands for Joint Photographic Experts Group, after the scientists and mathematicians who thought up the idea). JPG is known as a "lossy" compression because, when photographs are squeezed this way, some information is lost and can never be restored. High-resolution JPGs use lots of memory space and look very clear; low resolution JPGs use much less space and look more blurred.
Most digital cameras have settings that let you take pictures at higher or lower resolutions. If you select high-resolution, the camera can store fewer images on its memory card—but they are much better quality. Opt for low-resolution and you will get more images, but the quality won't be as good. Low-resolution images are stored with greater compression.
Turning ordinary photos into digital photos
There is a way to turn photos from an ordinary film camera into digital photos—by scanning them. A scanner is a piece of computer equipment that looks like a small photocopier but works like a digital camera. When you put your photos in a scanner, a light scans across them, turning them into strings of pixels and thus into digital images you can see on your computer.
Inside a digital camera
Ever wondered what's inside a digital camera? What takes the photo? Where's it stored? What makes the flash work? And how do all these bits connect together? When you take electronic gadgets apart, they're much harder to understand than ordinary machines (things that work through a clear physical mechanism): you can't always see which part does which job or how. Even so, it can be quite illuminating to peer into your favorite gadgets to see what's hiding inside. I don't recommend you try this at home: opening things up is the quickest way to invalidate your warranty; it's also a good way to ensure they'll never work again!
The main parts of a digital camera
We've opened up the camera in our top photo—and these are the parts we've found inside:
1. Battery compartment: This camera takes two 1.5-volt batteries, so it runs on a total voltage of 3 volts (3 V).
2. Flash capacitor: The capacitor charges up for several seconds to store enough energy to fire the flash.
3. Flash lamp: Operated by the capacitor. It takes a fair bit of energy to fire a xenon flash like this, which is why a lot of indoor flash photography quickly uses up your batteries.
4. LED: A small red LED (light-emitting diode) indicates when the self-timer is operating, so you can take photos of yourself more easily.
5. Lens: The lens catches light from the object you're photographing and focuses it on the CCD.
6. Focusing mechanism: This camera has a simple switch-operated focus that toggles the lens between two positions for taking either close-ups or distant shots.
7. CCD: This is the light-detecting microchip in a digital camera. You can't actually see the CCD in this photo, because it's directly underneath the lens. But you can see what it looks like in our article on webcams.
8. USB connector: Attach a USB cable here and connect it to your computer to download the photos you've taken. To your computer, your camera looks like just another memory device (like a hard drive or a flash memory).
9. SD (secure digital) card slot: You can slide a flash memory card in here for storing more photos. The camera has a very small internal memory that will store photos too.
10. Processor chip: The camera's main digital "brain". This controls all the camera's functions. It's an example of an integrated circuit.
11. Wrist connector: The strap that keeps the camera securely tied to your wrist attaches here.
12. Top case: Simply screws on top of the bottom case shown here.
Another important part, not shown here, is the LCD display that shows you the photos you've taken. It's mounted on the back of the electronic circuit board so you can't see it in this photo.
A brief history of photography
1. Steven Sasson's electronic digital camera patent from 1977.
2. 4t