# How many nodal and antinodal lines are there?

1. Jan 2, 2013

### Ilan

1. The problem statement, all variables and given/known data
In an interference pattern produced by two point sources separated by 3.5cm and vibrating in phase, the first order nodal line forms an angle of 20 degrees with the perpendicular bisector of the line segment joining the two sources. What is the wavelength? How many nodal and antinodal lines are there?

2. Relevant equations
PD = m * lambda
PD = d * sin(theta)

3. The attempt at a solution
3.5sin20=0.5lambda
lambda = 2.4cm

I'm not sure how to go about calculating the number of lines. The answer is up to first order antinodal and up to 2nd order nodal.

2. Jan 2, 2013

### PeterO

Nodal lines occur in places where the path difference from the sources is 0.5λ, 1.5λ, 2.5λ, ...

If your wavelength of 2.4cm is correct, that means 1.2cm, 3.6cm, 6.0cm , etc .

How do those differences fit alongside a source separation of 3.5 cm ?

Note: I have not checked, at all, the correctness of your λ = 2.4cm answer