Light travels at a speed of in vacuum. Light travels at different speeds in different materials because as the light enters any material the atoms of the material absorb, scatter and remit light. Therefore, when it travels from one medium to another, the speed either increases or decreases. The amount by which its speed changes determines the amount by which it will change its direction.
The speed of light in vaccum is . The speed of light in a transparent medium such as glass, water or clear plastic is less than this. To calculate the amount by which the ray will deviates from its path we use a physical quantity known as refractive index. It is the ratio of the speed of light in vacuum to the speed light in that medium. As the refractive index is a ratio of two same quantities that is speed it does not have any units.
where c = the speed of light in vacuum and v = the speed of light in the medium.
In all material media the speed of light is less than c. Hence, the refractive index of a material medium is greater than 1. The speed of light in air at atmospheric pressure is very close to that in vacuum, and we generally take the refractive index of air as 1.
The refractive index of water is about 1.33, and that of ordinary glass and diamond are about 1.50 and 2.42 respectively.
Larger the refractive index of a medium, greater is the bending of light when it enters the medium from air obliquely. Thus light bends more when it enters a diamond than when it enters an imitation jewel made of glass.
Illustration:: A ray of light enters a diamond from air. If the refractive index of diamond is 2.42, by what per cent does the speed of light reduce on entering the diamond?
Solution:
The speed of light in diamond is therefore 41% of its speed in air. In other words, in diamond, the speed reduces by 59%.
When the refractive index is considered with respect to the vacuum, it is called absolute refractive index.
When the light travels from one medium to another medium, the extent of bending of light depends on the refractive index of medium 1 with respect to the refractive index of medium 2. When the light is going from medium 1 to medium 2, the ratio of refractive index of medium 2 to the refractive index of medium 1, is known as relative refractive index.
So we can say that refractive index of medium 2 w.r.t. the refractive index of medium 1 is ratio of speed of light in medium 1 to the speed of light in medium 2.
Illustration:: Find the refractive index of glass w. r. t. water. The refractive index of glass and water w. r. t. air are 3/2 and 4/3 respectively.
Solution: We know that
Here glass is the second medium
And water is the first medium
Illustration: If is the refractive index of medium 2 with respect to medium1, is the refractive index of medium 3 with respect to medium2, and is the refractive index of medium 1 with respect to medium3, then prove that
Solution: We know that refractive index of medium 2 with respect to medium 1
..........[ I ]
And refractive index of medium 3 with respect to medium 2
..........[ II ]
And refractive index of medium 1 with respect to medium 3
..........[ III ]
Using I, II and III, we get
Hence Proved.
In the case of refraction, the ratio of refractive index of medium 2 to the refractive index of medium 1, is known as ___________________ . | |||
Right Option : B | |||
View Explanation |
If the refractive index of benzene is 1.50, then speed of light in benzene is | |||
Right Option : C | |||
View Explanation |
The ratio of the speed of light in two media is 9:12 . The ratio of their refractive index is | |||
Right Option : B | |||
View Explanation |
Third consective year,my ward is in Abhyas with nice experience of admin and transport support.Educational standard of the institute recumbent at satisfactory level. One thing would live to bring in notice that last year study books was distributed after half of the session was over,though study ...
The experience was nice. I studied here for three years and saw a tremendous change in myself. I started liking subjects like English and SST which earlier I ran from. Extra knowledge gave me confidence to overcome competitive exams. One of the best institutes for secondary education.
Abhyas institute is one of the best coaching institute in the vicinity of Ambala cantt.The institute provides good and quality education to the students.The teachers are well experienced and are very helpful in solving the problems. The major advantages of the institute is extra classes for weak...
About Abhyas metholodology the teachers are very nice and hardworking toward students.The Centre Head Mrs Anu Sethi is also a brilliant teacher.Abhyas has taught me how to overcome problems and has always taken my doubts and suppoeted me.
My experience with Abhyas academy is very good. I did not think that my every subject coming here will be so strong. The main thing is that the online tests had made me learn here more things.
It has a great methodology. Students here can get analysis to their test quickly.We can learn easily through PPTs and the testing methods are good. We know that where we have to practice
My experience with Abhyas is very good. I have learnt many things here like vedic maths and reasoning also. Teachers here first take our doubts and then there are assignments to verify our weak points.
When I have not joined Abhyas Academy, my skills of solving maths problems were not clear. But, after joining it, my skills have been developed and my concepts of science and SST are very well. I also came to know about other subjects such as vedic maths and reasoning.
I have spent a wonderful time in Abhyas academy. It has made my reasoning more apt, English more stronger and Maths an interesting subject for me. It has given me a habbit of self studying
We started with lot of hope that Abhyas will help in better understnding of complex topics of highers classes. we are not disappointed with the progress our child has made after attending Abhyas. Though need to mention that we expected a lot more. On a scale of 1-10, we would give may be 7.
Abhyas is good institution and a innovative institute also. It is a good platform of beginners.Due to Abhyas,he has got knoweledge about reasoning and confidence.My son has improved his vocabulary because of Abhyas.Teacher have very friendly atmosphere also.
My experience was very good with Abhyas academy. I am studying here from 6th class and I am satisfied by its results in my life. I improved a lot here ahead of school syllabus.
In terms of methodology I want to say that institute provides expert guidence and results oriented monitering supplements by requsite study material along with regular tests which help the students to improve their education skills.The techniques of providing education helps the students to asses...
A marvelous experience with Abhyas. I am glad to share that my ward has achieved more than enough at the Ambala ABHYAS centre. Years have passed on and more and more he has gained. May the centre flourish and develop day by day by the grace of God.
Abhyas is a complete education Institute. Here extreme care is taken by teacher with the help of regular exam. Extra classes also conducted by the institute, if the student is weak.
My experience with Abhyas Academy has been very good. When I was not in Abhyas whenever teacher ask questions I could not speak it confidently but when I came in Abhyas, my speaking skills developed and now I am the first one to give the answer of teachers question.
Usually we see institutes offering objective based learning which usually causes a lag behind in subjective examinations which is the pattern followed by schools. I think it is really a work of planning to make us students grab the advantages of modes of examination, Objective Subjective and Onli...
Abhyas Methodology is very good. It is based on according to student and each child manages accordingly to its properly. Methodology has improved the abilities of students to shine them in future.
It was a good experience with Abhyas Academy. I even faced problems in starting but slowly and steadily overcomed. Especially reasoning classes helped me a lot.
One of the best institutes to develope a child interest in studies.Provides SST and English knowledge also unlike other institutes. Teachers are co operative and friendly online tests andPPT develope practical knowledge also.