Question

Using a swimming pool, two students decide to test the water by setting up an interference pattern at one end of the 50 m pool. They sit 2.0 m apart and create waves by tapping their right foot, in phase with each other, onto the water at a frequency of 1.0 Hz. The speed of the waves is measured to be 0.60 m/s. The teacher is standing at the other end of the pool watching the pattern that is created and decides to count the number of nodal lines present. What is the total number of nodal lines present in the pattern generated?

Answer 1

nodal line: positive reinforcement.

d sinTheta=m*lambda where m=0,1,2,3

d=2, lambda=.6m

sinTheta=m*.6/2= .3m
for m=0, first nodal line
for m=1, second notal, solution exists
for m=2, third nodal, solution exists
for m=3, fourth line, sinTheta=1.2, no solution

so he sees middle nodal, then two to each side, total five.
http://www.pa.msu.edu/courses/2000fall/PHY232/lectures/interference/twoslit.html