# Light waves through grating. Min and Max measurements of wavelenghts in nm

#### Mugen112

1. The problem statement, all variables and given/known data
Light passes through a 220 lines/mm grating and is observed on a 1.4m wide screen located 1.2m behind the grating. Three bright fringes are seen on both sides of the central maximum.

What are the minimum and maximum possible values of the wavelength?
2. Relevant equations
y=LtanØ
dsinØ=m*wavelength

3. The attempt at a solution

I started by looking at the first equation that is listed. y=LtanØ
To find y, I just looked at the 220lines/mm and that is .00022lines/nm. So then I just converted L into nm and plugged in the numbers.

700000000 = 1200000000tanØ
then
tan-1(700000000/1200000000) = about 30 degrees???? ... I then put that into the second equation and get something wayyyy off for the wavelength. like .00037nm!?!
I've been working on this problem for over an hour and can't seem to find what I'm doing wrong or how to approach this the correct way. Any help is appriciated. Thanks!!!

Last edited:
Related Introductory Physics Homework News on Phys.org

#### Carid

d is the distance between two lines in the grating (hint: it is not a density)

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving