# Wave Interference Question

1. Oct 2, 2009

### wilson_chem90

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

A two-point source operates at a frequency of 1.0 Hz to produce an interference pattern in a ripple tank. The sources are 2.5 cm apart and the wavelength of the waves is 1.2 cm.

Calculate the angles at which the nodal lines in the pattern are far from the sources. (Assume the angles are measured from the central line of the pattern).

Relevant equations:
dsinO = (n-1/2)(wavelength)

O = angle theta

3. The attempt at a solution

my problem is that i can't figure out how many nodal lines there are in order to do the question. I know once i rearrange the equation i can find the angle, by the way i rearranged it to be O = sin inverse [(n-1/2)(wavelength)/d}.

2. Oct 2, 2009

### Delphi51

Just go on n = 1, 2, 3, ... until your calculator blows up!
(that is, until you get a sine value greater than 1).
You must have missed drawing all those crest circles and interference lines in high school. You can actually see a pattern and get a formula for the number of lines. I think it is 4 times the number of wavelengths of separation, counting both destructive and constructive lines.

3. Oct 3, 2009

### wilson_chem90

Sorry, i'm still not following unfortunately..

4. Oct 3, 2009

### Delphi51

dsin A = (n-1/2)(wavelength)
sin A = (n-1/2)(wavelength)/d
A = inverse sin[(n-1/2)(wavelength)/d]
When n = 1, A = invSin(1/2*1.2/2.5) = invSin(0.24) = 13.9 degrees
When n = 2, ...

5. Oct 3, 2009

### wilson_chem90

ohh okay i thought thats what you meant. So i honestly just keep doing that until i get to a whole number?

6. Oct 3, 2009

### Delphi51

Yes, keep going. You'll know when to stop.