# Find the wavelength or speed of the waves

1. Jan 8, 2007

### megashell

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

In a large water tank experiment, water waves are generated with straight, parallel wave fronts, 3.00 m apart. The wave fronts pass through two openings 5.00 m apart in a long board. The end of the tank is 3.00 m beyond the board. Where would you stand, relative to the perpendicular bisector of the line between the openings, if you want to receive little or no wave action?

2. Relevant equations

P(n) * S(1) - P(n) * S(2) = (n - 1/2) * wavelength

sin ANGLE(n) = (n - 1/2) * wavelength / (distance between sources)

x(n) / L = (n - 1/2) * wavelength / (distance between sources)

3. The attempt at a solution

I really have no idea how to go about this. I've read through the section (Nelson Physics 12 text book) three or four times now. I don't see how the equations relate. The sample questions are similar, except they just ask to find the wavelength or speed of the waves. I know the answer is 1.25 m (from the back of the book), but I haven't a clue how to get it. Any help would be great! Thanks!

2. Jan 8, 2007

### cristo

Staff Emeritus
The third equation gives you a formula for deconstructive fringes. Try that.

3. Jan 8, 2007

### megashell

But w hat do I use for x(n) and L?

4. Jan 8, 2007

### cristo

Staff Emeritus
Isn't x what you want to find out? If so, I'd say L was the distance from the board to the back of the tank.

5. Jan 8, 2007

### megashell

When I use 1 for n, I get 0.9. 2 for n, 2.7.

6. Jan 8, 2007

### cristo

Staff Emeritus
Hmm, I'm not too sure then. What do the symbols on the left hand side of your first equation mean?

7. Jan 8, 2007

### megashell

x(n) is the perpendicular distance from the right bisector to the point on the nodal Line
L is the distance from the point P(n) to the midpoint between the two sources