# Physics Learning Center

## 9 Common Questions of a Double Slits

physics.fisikastudycenter.com,-Learning 9 common questions of a double slits experiment, the bright fringe distance, the dark fringe distance, the distances between certain fringes and the maximum number of fringes seen on the screen will be discussed.

Problem
Given two slits and a screen of 80 cm away at an interference experiment below.

If the light used has 6000Å of wavelength and the two slits are 0,6 mm aprat, find the 9 items below :
1) the distance of the second bright fringe from the central fringe
2) the distance of the fourth bright fringe from the central fringe
3) the distance between the second and the fourth bright fringe
4) the distance of the fifth dark fringe from the central fringe
5) the distance of the second bright fringe from the fifth dark fringe
6) the distance between two bright fringes (one bright fringe to the next)
7) the distance between two dark fringes (one dark fringe to the next)
8) the distance between a bright fringe to the next dark fringe
9) the number of bright fringes seen on the screen

The given data:
screen distance → L = 80 cm = 0,8 m = 8 x 10−1 m
two-slits distance → d = 0,6 mm = 6 x 10−4 m
light wavelength → λ = 6000 Å = 6000 x 10−10 m = 6 x 10−7 m

1) the distance of the second bright fringe from the central fringe → n = 2, bright

2) the distance of the fourth bright fringe from the central fringe → n = 4, bright

3) the distance between the second and the fourth bright fringe

4) the distance of the fifth dark fringe from the central fringe → n = 5, dark

Catatan :
When you use the equation dY/L = (n + 1/2) λ for this question, for the fifth dark fringe use n = 4

5) the distance of the second bright fringe from the fifth dark fringe

6) the distance between two bright fringes (one bright fringe to the next)
Take the distance of the first bright fringe from the central fringe, where the central fringe is at distance "0", so we just need to find the first bright fringe distance from the central :

7) the distance between two dark fringes (one dark fringe to the next)
Is it the same with the distance between two bright fringes distance? Think about it!

8) the distance between a bright fringe to the next dark fringe
Take the distance difference between the firs dark fringe distance and the central:

9) the number of bright fringes seen on the screen

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