# Thread: Fringe pattern of a sodium lamp

1. ## Fringe pattern of a sodium lamp

1. The problem statement, all variables and given/known data
Hi
Please, what fringe pattern would be obtained with a sodium vapour lamp?

2. Relevant equations

3. The attempt at a solution
I am guessing that a dominant yellow colour would be obtained. The sodium is almost acting like a monochromatic light and therefore has a particular wavelength. But I am not sure how correct my answer is. Also, what will the sketch look like? Please comment

2. Originally Posted by gbenguse78
1. The problem statement, all variables and given/known data
Hi
Please, what fringe pattern would be obtained with a sodium vapour lamp?

2. Relevant equations

3. The attempt at a solution
I am guessing that a dominant yellow colour would be obtained. The sodium is almost acting like a monochromatic light and therefore has a particular wavelength. But I am not sure how correct my answer is. Also, what will the sketch look like? Please comment
There must be more to this than what you have posted, we need the context to determine what fringes you are talking about.

Sodium light is for most purposes monochromatic as you say.

CB

3. The full question is: Sketch an arrangement that may be used to observe the fringe pattern when light from a narrow slight slit illuminated by a sodium vapour lamp is passed through a pair of double slits.
Describe the fringe pattern you would expect to observe.

Does this help?

4. Originally Posted by gbenguse78
The full question is: Sketch an arrangement that may be used to observe the fringe pattern when light from a narrow slight slit illuminated by a sodium vapour lamp is passed through a pair of double slits.
Describe the fringe pattern you would expect to observe.

Does this help?
Yes, it is asking for the two slit fringe pattern.

The fringes occur in those directions for which the light from the slits is in phase.

Draw a diagram, then to be in phase in a direction $\theta_n$ requires that the triangle shown in the diagram is a right triangle.

CB

5. Thanks. So the angle theta is adjacent to d?

6. Originally Posted by gbenguse78
Thanks. So the angle theta is adjacent to d?
Yes

CB

7. Thanks a lot. Got my exam by 1pm today.