00:01
So in this question, we have the double straight interference, and we first do it with a red laser, and then we replace the laser with another different laser, and we find that the separation between different fringes become different.
00:18
And from how the separation between fringes change, we want to know what is the wavelength of the other light.
00:25
So, this is a usual graph we have.
00:32
Light, light, theta, theta.
00:37
And again, we are just right down our user relationships that d times sine theta equals m times lambda.
00:48
In this case, we do not know what d is, and then with sine theta is roughly equals x2 over l, we also do not know what l is.
01:06
So we have limited information.
01:07
But let's first just write down everything.
01:10
So it's d times x over l when we when i plug the slumber inside equals m lambda and that gives me x equals m lambda l over d.
01:24
So here let's see, let's take a look at this.
01:28
We're looking, we're given 5 millimeter is the space between red fringes.
01:37
So like between between two red fringes, the m is different by one.
01:45
So delta x, this is like, when you have two different fringes, this is the second order and this is a third order, there, this is just an example, it could be the first or the second.
01:58
So delta x will be lambda l over d, because in this case, m equals one.
02:05
And you can see that in some way, delta x is proportional to lambda.
02:13
So we can find this.
02:15
Right now, what we have is we have 5mm...