# Determine ruling from grating constant

1. Oct 20, 2014

### Alexandra7

1. The problem statement, all variables and given/known data
If "d" is the grating constant, determine the ruling (number of lines/grooves per meter) "D"

2. Relevant equations
I have spent hours researching sites that are far too complicated for my understanding of physics. As a result the only relevant equation I could remotely relate to this problem is as follows:

N= 1/d

3. The attempt at a solution

N= 1/1.6555x10^-6m
= a really big number! such as 604,230 grooves/m or lines/m

It just doesn't make sense and I'm getting upset!
Please, pretty please with a cherry on top, is anyone able to help me? Physics is by far my worst subject but I'm trying!

2. Oct 21, 2014

### Staff: Mentor

Seems like it might be OK to me. 604,000 grooves/m is 6040 grooves in a centimeter. You didn't give the grating constant in your problem statement, but assuming that number is correct and your formula is correct, I don't see a problem. Do you have the answer available?

3. Oct 21, 2014

### Alexandra7

First of all, thank you for your contribution.

Unfortunately my textbook does not include a solutions manual so I can only try, then hope for the best. My professor said we would have a question similar to this one on a test which is why I'm freaking out.

The grating constant is 1.6555x10^-6m

4. Oct 21, 2014

### haruspex

If the grating constant is the gap between consecutive lines then the number of lines per unit distance is clearly just the inverse of this. Your answer must be right.

5. Oct 21, 2014

### Simon Bridge

... you are going to have to get used to how numbers behave.
Try checking your reasoning with something you are more used to:

If d=1mm, then N=1000 lines/meter right?
The short lines on a meter-rule are 1mm apart: how many of them are there?

For your example, d ~ 1000th of a millimeter - so how many lines are there in 1mm?
... how many of those groups are in 1m?
... so how many overall?

You actual d is slightly bigger than that so you'd get slightly fewer lines per meter - is your number consistent?