Slits per cm on diffraction grating

[msk172]

Homework Statement

Light of 650 nm can be seen in three orders in a particular grating. About how many slits per cm does this grating have?

Homework Equations

Yikes.

The Attempt at a Solution

Either this question is ridiculously hard resulting in me not even having a clue where to start, or it is so easy that I don't even deserve to get it right.. haha. If someone could just point me towards the right CONTINENT, I might have a chance.. heh. Thanks in advance.

 

[Redbelly98]

I would start with the diffraction grating equation, which relates the angles of different order beams to the wavelength, slit spacing, and order #.

This question is not as bad as it seems at first.

More info:
https://www.physicsforums.com/library.php?do=view_item&itemid=201

 

[msk172]

I understand that, but without knowing the length of the grating, how could one possible ascertain slits / cm?

 

[Redbelly98]

The equation gives you the distance between adjacent slits. Take the reciprocal of that distance (in cm), and you get the number of slits per cm.

 

[msk172]

Got it. Ugh. Too many hours of looking at this screen. Thanks for your time.

 

[Redbelly98]

You're welcome, no problem.