# B What does coefficient of increase of physical quantity mean?

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1. May 13, 2018

### Nabin kalauni

I am extremely confused by the use of the term coefficient of increase of something. For example , if it is stated that the index of refraction varies linearly with a coefficient of 2.5×10^-5, how is this coefficient defined? Is it simply the slope of the line plotted with index of refraction on y axis and temperature on x axis? Or is it defined like in the case of coefficient of linear expansion?
α = Δn/ΔT or α = Δn/nΔT?
P.S. I am not sure if this falls under mathematics or physics. Excuse me if I posted it on the wrong topic.

2. May 13, 2018

### sophiecentaur

That's not a term I have come across but I can see it comes from the assumption that there's a linear relationship between one quantity and another.
y=y0 + Bx (sloppy terminology, perhaps but it contains the message)
A coefficient can be positive or negative, of course and positive would be the assumption if there is no explicit sign.
In the case of refractive index you quote, your coefficient corresponds to the dispersion relative to the value at a particular wavelength.
Have you looked at coefficient of thermal linear expansion? Hyperphysics is always a good source of this sort of information.

3. May 13, 2018

### Staff: Mentor

Usually the units can help you understand. What are the units of this coefficient you mentioned?

4. May 16, 2018 at 2:09 AM

### Nabin kalauni

Cool. The unit given was K^-1. So that must mean the latter definition works. Thank you.