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.