Answer
$ 1.17mm$
Work Step by Step
First, we use a trig ratio to relate the angle, the distance to the minima, y, and the length to the screen, L.
$\sin \theta =y/L$
Now we can use the above relationship and the give values in equation (36-3) to solve for the distance to the minima, y,
Therefore;
$\alpha \sin \theta = \Delta m \lambda $ where $m=1,2,3,....$ (minima)
$\alpha (y/L) = \Delta m \lambda $
$y = \Delta m \lambda L / \alpha $
$y = (2-1) 589*10^{-9}m *3.00m / 0.001m $
$y = 1.17*10^{-3}m$
$y = 1.17mm$
