In a double slit interference experiment, the separation between the slits is 1.0 mm, the wavelength of light used is 5.0 × 10-7 m and the distance of the screen from the slits is 1.0 m. (a) Find the distance of the center of the first minimum from the center of the central maximum. (b) How many bright fringes are formed in one centimeter width on the screen?
Given, separation between the slits 
wavelength of light used, 
The distance between the screen and the slit, 
(a)Here, we first find the distance between two consecutive maximal and then divide it by 2 to obtain the distance of the center of the first minimum from the center of the central maximum.
(b) The width of one fringe is 
Therefore, number of such fringes present in 1 cm region is 
.
Therefore, 20 such fringes will be present.