# Homework Help: Lloyd single Mirror

1. Dec 2, 2012

### merc90

1. The problem statement, all variables and given/known data: In a loud single mirror exp. a bright fringe of width 0.2 mm is seen at a point on the screen kept at a distance 1.0 m from the source. When the mirror is raised up to increase the angle of incidence at any point of the mirror by a dist. of 0.9 mm, fringe width of the same fringe becomes 0.5 mm, find the wavelength of the source.

2. Relevant equations: wavelenght = distance between the two slits (a) * fringe width (X) / distance from source to screen (D)

3. The attempt at a solution: How to find the distance between the two slits? Should I be proceeding by finding "a" by a= incidence angle*D?

2. Dec 2, 2012

### Redbelly98

Staff Emeritus
Welcome to Physics Forums.

You can use the first equation you wrote,
... and write it twice, because there are two situations:
(1) the distance between the "slits" is a
(2) the distance between the "slits" is ____ [where you fill in the blank here].

3. Dec 2, 2012

### merc90

Thanks Redbelly98 for the quick reply.

Is the answer: wavelength = 6000 A correct?

Steps:
wavelength = 2*a*X/D
Therefore, 2*a*0.2/1000=2*(a-0.9)*0.5/1000
which gives, a=1.5 or 2*a = 3.0
so, wavelength =3.0*0.2/1000
=6000 A

4. Dec 2, 2012

### Redbelly98

Staff Emeritus
Looks good!

You may need to better explain how you worked the units, if you submit your homework to be graded or have to work a similar problem on an exam someday.