# Light problem -- diffraction grating distance between adjacent bright fringes

1. May 1, 2015

### student07

1. The problem statement, all variables and given/known data
Light from a laser with a wavelength of 760 nm is directed at a diffraction grating of 1500 lines/cm. If the diffraction grating is located 1.5 m from the screen, calculate the distance between adjacent bright fringes.

2. Relevant equations
Δx = Lλ / d
760 nm = 7.60 x 10^-7 m = λ
1.5 = L
1cm/1500 = 6.67 x 10^-6 m = d

3. The attempt at a solution
Δx = (1.5 m)(7.60 x 10^-7 m) / (6.67x 10^-6 m) = 1.71 x 10^-13 m

2. May 1, 2015

### ehild

Can it be correct? You see the bright fringes on the screen. Their distances is in the range of mm or cm, Can 10-13 m true???

3. May 1, 2015

### student07

I saw other people getting 1.72 cm which is 0.0172 m but the the answered I wrote is what I got in the calculator so I'm not sure how they got that

4. May 1, 2015

### ehild

You typed in wrong number in the calculator when you divided by 6.67x10-7.

I guess you did not use parentheses.

Last edited: May 2, 2015
5. May 2, 2015

### BvU

Dear sudent,

you want to avoid this kind of disaster by estimating the outcome of a calculation before using an electronic calculator. In this case you divide 7.6 by 6.7 which is a little more than 1, and 10-7 by 10-6 which is 10-1.
Times 1.5 should give a little over 0.15. So your answer is 17.1 cm.

6. May 2, 2015

### student07

actually Ehild was right I did not use parenthesis when I divided by 6.67x10-7 so the actual answer is 0.171 m.

Thank you for your help guys!