# Two-slit interference

1. May 3, 2009

### fwFAWFSERG

SOLVED

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

A two-slit interference set-up with slit separation d =0.30 mm produces interference fringes at a particular set of angles THETAm (where m = 0, 1, 2,) for red light of frequency f = 4.9×10^14 hz.

If one wishes to construct an analogous two-slit interference set-up that produces interference fringes at the same set of angles THETAm for room-temperature sound of middle-C frequency f = 262 hz, what should the slit separation distance be for this analogous set-up?
this particular problems answer is 640 but i cant seem to arrive at that
2. Relevant equations
sin(theta)= m(wavelength)/d

3. The attempt at a solution
i believe sin(theta) is equalin both, so i dont see why it wouldnt come down to wavelenth/d is proprotional to wavelenth/d, or converting to frequency 1/fd = 1/fd or fd=fd.

Last edited: May 3, 2009
2. May 3, 2009

### nickjer

You know $$\lambda = v/f$$, but they both have different velocities so you can't use fd = fd.

3. May 3, 2009

### fwFAWFSERG

arent their velocities equal at c, being the speed of light?

4. May 3, 2009

### nickjer

Sound doesn't travel at the speed of light. At least not where I live at.

5. May 3, 2009

### fwFAWFSERG

oh that is quite true, shouldnt have overlooked that, so i can now say the formula is
c/fd = 343/fd?

edit: yes i can, thanks alot nickjer, i got it now.