Quality of Lenses Using Newton's rings

AI Thread Summary
The discussion focuses on using Newton's rings to assess lens quality, specifically examining the relationship between ring width and lens perfection. It is noted that equal widths of the fringes indicate a perfect lens, but there is uncertainty about deriving a numerical value for lens quality. A suggested formula for calculating the radius of the nth dark ring is r_n = √(nRλ), where λ is the light wavelength and R is the lens radius of curvature. The possibility of using the lens maker's equation was also considered, although the limited use of one lens per set of rings complicates this approach. Overall, the conversation seeks clarity on quantitative methods for evaluating lens quality through experimental data.
wilsonge
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Homework Statement


Basically I'm writing up a formal report on our experiment on Newton's rings - one of the things in our aims was in investigate the quality of the lenses we were using. Whilst many sites also say Newton's rings can be used to investigate the quality of the lenses not much further information was given and I couldn't find anything in our lab sheet.

So far I think I've gathered from my research that its to do with the width of the rings produced (i.e. equal widths of the fringes means a perfect lens). However I am unclear as to what the exact process is to getting a numerical value of the quality of the lens - is there a equation somewhere that I'm missing? If there is no equation can I express this numerically with some kind of units?

Homework Equations


Good Question :) Are there any?

The Attempt at a Solution


Not really applicable but see above - cause my question is littered with the limited research I've found

Sorry this isn't really layed out in quite the way you want it - but it isn't really algebra either :)

Thanks in advance for any help given,
George

P.S. Not sure if this should have gone in the undergraduate section - sorry if its in the wrong place!
 
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Been thinking a bit more about this and I'm wondering could I use the lens maker's equation and then use the difference in the refractive index - only problem is I only used one lens for each set of Newton's Rings formed so not sure if that gets me anywhere or not

George
 
The radius of the nth dark ring is given by

r_n = \sqrt{n\;R\;\lambda}

where \lambda is the wavelength of light and R the lens radius of curvature. I suppose you could calculate R for each measured rn and then provide a standard deviation figure or some such.
 
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