Double slit and colored wavelength

1. Nov 17, 2008

Kris1120

1. The problem statement, all variables and given/known data

White light spans the wavelength range be-
tween about 400 nm and 700 nm.
If white light passes through two slits
0.656 mm apart and falls on a screen 1.7 m
from the slits, what is the distance between
the first-order violet and the first-order red
fringes?

2. Relevant equations

sin(theta) = m*lambda / d

x = L*tan(theta)

3. The attempt at a solution

I used the first equation to solve for theta for both red light (lambda = 700 nm) which gave theta = .061139 and violet light (lambda = 400 nm) which gave theta = .034936. I used the second equation to plug in theta and solve for x for each of them. I then subtracted the x value of violet from the x value for red and converted to mm. My final answer was 6.781 mm.

2. Nov 17, 2008

alphysicist

Hi Kris1120,

Can you show the steps in how you got 6.781mm? That does not look right to me.

3. Nov 17, 2008

Kris1120

theta(red) = inverse sin (700 e-9 m / .656 e-3m) = .061139 degrees
x=tan(.061139)*1.7m = .007818

theta(violet)= inverse sin (400 e-9 m / .656 e-3 m) = .034936 degrees
x=tan(.034936)*1.7m = .001037

.007818 - .001037 = .006781 m = 6.781 mm

4. Nov 17, 2008

alphysicist

I'm getting 0.001814 for this. Would you check it again?

5. Nov 17, 2008

Kris1120

yes! I hate when I do silly things like that! Thank you for correcting me!