# Lenses often contain thin coatings to reduce reflections...

1. Feb 14, 2017

### AlexisFair

1. The problem statement, all variables and given/known data

Lenses often contain thin coatings to reduce reflections and UV radiation. Explain how this works.

2. Relevant equations

3. The attempt at a solution
To reduce reflections on lenses, known as back-glare, they are often coated in what is called anti-reflective (AR). The AR causes the intensity of light reflected from the inner surface and the light reflected from the outer surface of the film to be nearly equal. The two reflections from each side of the film cancel each other out through destructive interference therefore decreasing the glare. In short, AR works by shifting the light waves out of phase resulting in destructive interference minimizing the glare. As the reflections are cancelled, energy still has to go somewhere and thus transmits into the lenses. In addition, most UV blockage is done by making the lens from a material that absorbs UV radiation.

This question is very simple for a lot of my classmates but I ten too lose marks on these types of questions as english is not my second language. But yes, is my answer correct and is it clear to read?

2. Feb 14, 2017

### kuruman

Your answer is clear to read as far as the English is concerned. Did you write it yourself? More importantly, do you understand what it is saying and do you think you will be able to solve a problem that requires you to use the ideas that your answer expresses?

3. Feb 14, 2017

### AlexisFair

Yes I did. I got some help from our text book but I did not want to plagiarize it. I use my own words as much as possible without changing any of the theories. Yes I do, for the most part I understand the concepts is just my english structure can sometimes mess up what I want to say when i write answers or do essays. Then again, I made this account to double check my work (Also, to gain some help if I'm unclear of something.) and to see if i have made a mistake and to see if i can include more or do more. I'm not the most smartest student but I'm willing to learn and try.

Should I include anything else? Maybe include "destructive interference is when one waves crest meets another waves troph" ?

Last edited: Feb 14, 2017
4. Feb 14, 2017

### kuruman

You have done well. Expressing these ideas in your own words helps your understanding. Yes, I think it will be a good idea to explain destructive interference and write an equation or two showing mathematically what is going on. Since you asked to correct your English, the crest of one wave meets the trough not "troph". If you want to include more, you need to understand more and perhaps go beyond your textbook. You can start here https://en.wikipedia.org/wiki/Anti-reflective_coating specifically section 3.3, "Interference coatings." I or someone else could re-check your answer if you choose to add more to it.

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