# Slit & light interference

1. Jan 31, 2013

### quicksilver123

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

Two narrow slits are cut into a sheet of paper and set in front of a laser beam, causing an interference pattern to appear on the wall.
If the distance from one slit to the third bright fringe is 0.5000004 m
and the distance from the other slit to the same bright fringe is 0.5000008 m
calculate the wavelength of the light from the laser.

2. Relevant equations

| PmS1 - PmS2 |= m$\lambda$

3. The attempt at a solution

|0.5000004-0.5000008|=(3)$\lambda$
0.0000004/3 = $\lambda$
$\lambda$ = 0.000000133 m

| P3S1 - P3S2|
| PmS1 - PmS2|

How would I turn one into the other?

|0.50000030-0.50000165|=3$\lambda$
$\lambda$=0.00000135/3
$\lambda$=0.00000045m = 450nm

I'd like to know where they got the values of:

PmS1=0.50000030m
and
PmS2=0.50000165m

Last edited: Jan 31, 2013
2. Jan 31, 2013

### TSny

Did you leave out the "5" after the decimal points? Your work looks correct to me. I don't see where the book's numbers come from either.

3. Jan 31, 2013

### quicksilver123

didn's leave anything out :/

sorry, i edited my original post a second ago.

| P3S1 - P3S2|
| PmS1 - PmS2|

How would I turn one into the other?

4. Jan 31, 2013

### TSny

Is the distance from the first slit to the bright fringe 0.000004 m or 0.500004 m?

Let m = 3?

5. Jan 31, 2013

### quicksilver123

sorry, corrected the mistake.

the book has been known to make errors in their solutions... but i was wondering if there's something i'm missing

6. Jan 31, 2013

### TSny

I think your work is correct.

7. Jan 31, 2013

### quicksilver123

alright, thanks