This is an experiment to measure the wavelength and creating element. This is our creating element and this is the screen. M of the experiment is to measure the wavelength and the creating. So first of all, basically what we have to do, we will just find out the thing. Apprates, what apparatus basically we are using here? This is laser source. This one is the creating. I am using here this grating which have 15,000 lines per inch. This is our screen. So there are only three components into this apparatus. By using this we have to find out the wavelength and the grating element. So first of all we have to find out the wavelength. So this is the laser source as I said earlier. So this laser light basically falls only this grating element and as a result of it it is diffracted. And this diffraction pattern is developed. This bright is for this screen, this one, the central maxima. And here this is of the first order. This one and this is the first order diffraction. So what is the important point? To find the diffraction grating and the laser wavelength, we have to use a diffraction. This diffraction is basically that it is N lambda is equal to 2 d sin theta. So I can use this N lambda is equal to 2 d sin theta. So if suppose I want to find out this lambda. So how to find it? It means from the observation I have to find out this d, this theta and the order of N. So what is the order of N? N is the diffraction order which order basically we are considering. So suppose I am using N is equal to 1. What is it means? If I use N is equal to 2 then what is the meaning of it? N is equal to 1 and N is equal to 2. So N is equal to 1 means that this tiny, this is the central maxima. And this one is the first order diffraction. So this N is equal to 1. If I am getting one more here that will be N is equal to 2. And now then after how to find out this d? This d is the grating element and grating element one can find out with the help of grating. Now right now we have 15,000 lines per inch into the grating. So we know that 1 inch is equal to 2.54 centimeter and 1 centimeter. The number of lines basically in 2.54 centimeter are 15,000. So 15,000 lines means you have 15,000 slits of equal space. So I have to find out this one. Select of a slit width of this grating. So that is basically grating element. This is grating element. And for this particular it will be d 1 slit width, 1 slit width will be that is d will be equal to 2.54 centimeter upon 15,000 lines. So this will be the slit width. So by this way one can find out this d and how to find out theta. If you see carefully this experiment. The distance between the grating and this is grating that will be suppose capital D. This is the horizontal distance between the screen and between the grating. So this I can say this is capital D. So I am writing here this is capital D. That is the distance between the screen and the grating which we are using here. Now the next point is we are looking that this is our central maxima. This is our central maxima. And this one is the first order diffraction in both the side. This one and this one. So the average distance from the central maxima orbit that will be first we have to measure this distance then after this one and take the average orbit. So that will be Y. Now in first Y1 and Y2. Take the average orbit that will be Y. So this situation looks like here your screen this is the grating and this is central maxima. This one is the first order diffraction. So I am saying that the distance between grating and this screen is D and this distance is Y1 and Y2. So I am taking the average so that average will be this one. Now this is Y. So I have to find out this theta. So using tan theta, tan theta will be equal to Y upon D. And from here I can find out theta. Theta will be tan inverse Y upon D. And now I can use this theta into this diffraction formula. So by this way I can find out the lambda. So by this way one can basically do the calculation 40 wavelength and then compare with this standard value. So this is the way to find out the wavelength using this experiment.