# Homework Help: Light problem help.

1. Dec 8, 2009

### fallen186

1. The problem statement, all variables and given/known data
Light of wavelength 635 nm is used to illuminate normally two glass plates 16 cm in length that touch at one end and are separated at the other end by a wire of radius 0.02 mm. How many bright fringes appear along the total length of the plates?

2. Relevant equations
http://www.phys.washington.edu/users/savage/Class_123/Assigns_123_99/***_99_6/soln99_6/node6.html <-- Same problem except with different numbers and it has a shows solution.

$$2d = (m + \frac{1}{2})*\lambda$$

$$2* 0.04mm = (m + \frac{1}{2}) * 635 nm$$

$$\frac{0.08 mm}{635 nm} = (m + \frac{1}{2})$$

$$125.984 = m + \frac{1}{2}$$

m = 125.484 or 125

yet I get the answer wrong

2. Dec 8, 2009

### rl.bhat

Here m is not the number of bright fringes. What about the length 16 cm?