In the experimental setup, we use a sodium source of light. It gives an intensively bright golden yellow light. Ahead of this source of light, we have a single slits. It is rectangular and arranged vertically. It is nearly 1 mm wide. Symmetrically to S, there are two slits S1 and S2. Which are nearly 0.3 mm wide, the distance d between the two slits is nearly 1 mm. A screen is held parallel to the slits at a distance of nearly 2 meter.The above arrangement ensures that light waves coming from S1 and S2 in the same phase. So, S1 and S2 are coherent sources.Let us now consider a point P on the screen. When either S1 and S2 alone is open, there is a continuous full light all along the screen. However, when both the slits are open, this uniformity disappears. Instead, we have a set of alternate bright and dark vertical lines, equally thick and equally distant from each other. These are called interference fringes.In arriving at P, the waves from S1 and S2 have to travel different paths. So, the waves arrive at P with a certain path difference. If path difference is equal to nλor phase difference is 2nπ, then the two wave trains reinforce each other giving a fringe of high intensity.

ที่มา : http://www.youtube.com/channel/UCflmr7Tyyy38MaAENetim_g อัพโหลดโดย 7activestudio