Double slit

[deleted647690]

When you are trying to find the distance between fringes on the screen in this experiment, does the equation:

y=lamda*L / d

only work for fringes right next to eachother? So for example, you could use this to find the first fringe that appears away from the origin on the screen, but you couldn't use this to find the distance to the second fringe, because there is nothing in the equation that would vary. Lamda, L, and d are the same for every fringe.


The reason I ask is that BR uses the above equation I have provided, but after watching videos online, I have found that there is another set of equations used to solve this type of problem:

mlambda = dsintheta
y = L*theta


So is the first equation I provided only good for finding the distance to the first fringe displaced from the origin? (by origin, I mean the center line of light on the screen, in the middle of all of the other lines)

---

Members don't see this ad.

 

[sazerac]

When you are trying to find the distance between fringes on the screen in this experiment, does the equation:

y=lamda*L / d

only work for fringes right next to eachother? So for example, you could use this to find the first fringe that appears away from the origin on the screen, but you couldn't use this to find the distance to the second fringe, because there is nothing in the equation that would vary. Lamda, L, and d are the same for every fringe.


The reason I ask is that BR uses the above equation I have provided, but after watching videos online, I have found that there is another set of equations used to solve this type of problem:

mlambda = dsintheta
y = L*theta


So is the first equation I provided only good for finding the distance to the first fringe displaced from the origin? (by origin, I mean the center line of light on the screen, in the middle of all of the other lines)

You are flying too close to the border between mathematics (exact) and engineering ("good enough").

With the distances and angles involved in a typical double slit experiment, theta is so small that the following are all considered equivalent:
tan(theta)
sin(theta)
theta

Sure the simple physics equations derived for Young's experiment will start to fail towards the far edges (large thetas) of an experiment, but that isn't really relevant to a multiple choice exam that rewards fast approximations.