# Intensity and wavelength

1. Jan 15, 2009

### jullrich

1. The problem statement, all variables and given/known data: The diagram represents two coherent light sources emitting light of equal intensity and wavelength. The intensity of the light at point P is zero. Which of the following could be the difference in path length taken by the light in traveling from each source to point P?

2. Relevant equations: the diagram looks like a 3-4-5 triangle with the short side left off and where to two lines cross for a point on the opposite side to be point P. The length of one side is 4.3 cm and the other side is 5.1 cm.

3. The attempt at a solution: we know the answer is 1/2 lamda but have no idea how to how solve this ... please help
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jan 15, 2009

### kbaumen

Welcome to PF!

Do you know what is interference and what conditions must be applied for interference to occur?

3. Jan 15, 2009

### jullrich

No interference and no conditions.

4. Jan 15, 2009

### kbaumen

What do you mean no interference? You haven't studied it or it isn't the case here?

Check out when waves interfere to cancel each other. To understand this, you must know how to plot a graph for a wave. And if you could upload the diagram (the actual one or sketched in paint), it would be a bit easier to discuss the exercise. Just remember that nobody will solve it for you. People will only give you hints to help you better understand the exercise and solve it yourself.

5. Jan 15, 2009

### jullrich

The diagram looks like two rays from the same origin point.
The end of the rays would be the light itself.

6. Jan 15, 2009

### kbaumen

Well, you got me confused. At first you say that the diagram is a triangle but now you say that waves originate from the same point and meet at point P. For two waves two have an interference minimum (cancel out each other, hence have an intensity sum zero at an intersection point) they must be coherent and one must have the distance traveled by lamda/2 more. As much as I understand from your description of the exercise, this is what's asked. However, you have these 4.3 and 5.1 and I'm rather confused why.