Why coloured reflection on CDs and DVDs ?

Hey welcome, let’s ask questions what we see in our lives and understand physics based on that. Yesterday when I was watching a DVD I had seen colors on its surface I was amazed why I see colors on its surface and not on any other surface there must be amazing physics working behind this. Well, CDs and DVDs both the same but DVDs store more information as we all know hey again one more question why is that here we go we didn’t get an answer but now we have another question. Anyways let’s continue in our journey of finding answers. I know CDs is used to store information like audio, video blah blah blah information. Similarly like a magnetic tape, DNA molecules, phonographs, credit cards, etc. So form this we know we can store information in so many ways. Well in CDs or DVDs it’s done with lasers, reflection, refraction, interference of light, etc . However the information is stored in it. It is read by electronic circuitry. So let’s begin with it 
As we all know in all modern technology information is stored. In 0 and 1 and this means whatever is written in the disk is only 0 and 1.  here once and zeros are bits. And 8 bits make a byte. Whatever we store in computers is just a series of 0 and 1. So whatever is stored in CDs is just a very long number. A CD contains a 16-bits number which gives the intensity of sound. The CD holds 44,100 such numbers for each second of the music record. Actually, double of it cos we store music on two channels which we call as stereo all this is just a number so don’t be too concern about it 
The 0 and 1 can be coded as electrical switches that get on or off in computer memory. In CDs, the digital information is stored in tiny pits stamped into the plastic of the disc and covered with a thin metallic layer.
This pit is very tiny of range 1-3 mm and 1/2 mm wide. To give u an idea of how small it is the human hair is 100 mm in diameter. I hope this gives u an idea of how small this pit is. This pit lies in spiral tracks on the disc. Let’s talk about some statics fact in CDs there are 22,000 tracks and sum of all these tracks forms 3 miles. The more we make pits then more information we can store here we got a clue. 
In CDs this holed is larger than DVDs so that’s why DVDs store more information than CDs.
Now hold up a CD on your hands and u will see  in it. This is evidence for pits are they in CDs cos we can’t see these pits with our normal eyes. Now many of u think we got the answer actually sorry to say that we still so far from the answer which makes it more clear.
Then the information is read with the help of lasers. In CDs, the information is stamped from above but the disc is read it from below so for beam the pits appear as raised areas.
The beam of light is larger than pits. When light hits the flat area it gets reflected back but when it falls on pits edge. Interfere and scattering of light waves diminish the light we
intensity of the reflected light. (  about interference and dispersion of light in waves topic when we will discuss for now dispersion is spreading of light and interference is the property of waves it cancels each other.) Thus the presence of pits product various light patterns in CDs each pit edge means one and in-between area is zero. This pattern of varying light intensity is read as patters of zeros and ones and gets processed then it gets converted into an electrical signal. And sent to speaker or display 
Unlike other information storing devices, it can be coppoed number of times without losing its quality. Why is that cos in another device like magnetic tapes it’s gets affected with the magnetic field and inform stored in it’s become affected in CDs this is not a case cos its store’s information in such a way most of the physical phenomenon can’t affect its data. One of the most advantages of it is that its data can’t get affected by dust u like other data storing devices. Because pits are so tiny when dust particles fall on it the beam of the laser is larger than that of dust it’s somehow managed to focus on the pit. More about it we will discuss in when we discussed lights. 
 We have heard about recordable CDs – R discs it uses chemicals to become opaque when high power laser hits its surface the lager burns the information in it. You have heard about burning a disc before I’m sure. And when low power laser hits it’s surface it again able to read the information on it this CD can be used more than once but it has its limitations we can’t use it a number of times we want for that DVD- RW discs developed 
CDs and DVDs are amazing devices it’s no longer available or better say we don’t use it nowadays. Cos we got smaller information storing devices like pen-drive, memory chips, etc but this CDs uses simple laws of physic and made it applicable that’s Beauty of the human mind it has no limits 

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