Homework Help: Double Slit Problem Help

1. Aug 9, 2006

MD2000

In a Young's double-slit experiment, the seventh dark fringe is located 0.023 m to the side of the central bright finge on a flat screen, which is 1.1 m away from the slits. The separation between the slits is 1.5 10-4 m. What is the wavelength of the light being used?
m

I'm having some trouble understanding what exactly the equation is saying. I know I have to use sin theta = mlambda/d for the bright fringe and then sin theta = (m+1/2)lambda/d for the dark..but I'm not sure how to get theta..I figure I need to use the two initial values that I'm given but I'm not sure what those values exactly mean..any help?

2. Aug 9, 2006

Andrew Mason

Use:
$$\lambda = \frac{d\sin\theta}{(m+1/2)}$$ where $\sin\theta = .023/1.1$.

AM

3. Aug 10, 2006

sdekivit

draw yourself a triangle and note that $$sin \theta = \frac {d_{minumum-central finge}} {d_{slit-screen}}$$