Question

spectrograph

Your overall goal is to create a spectrum that is as bright and spread-out as possible so that the locations of hydrogen's spectral lines can be measured The basic idea is shown in the diagram at the bottom of this page. Light shines out from the hydrogen gas tube in all directions. Some of this light is "caught" by a lens called the collimator, which, if placed correctly, collimates light. Collimated light means light rays that are all parallel. This light (of all wave- lengths) enters the grating. The grating separates the light into slightly different angles depending on wavelength, but each wavelength is still collimated This wavelength-separated light now enters a lens called the camera, which fo- cuses each wavelength of light into specific real images on the screen (if the screen is placed correctly). Some questions to consider for your own spectrograph design: What kind of lens should the collimator be? And the camera? What would the effects be on the spectrum (and the subsequent measure- ments you could make on that spectrum) if the collimator had a shorter or longer focal length? Or if the camera had a shorter or longer focal length? If you had your choice of different focal lengths, what would be the better choices for the collimator and camera? Where do the gas tube, lenses, and screen need to be placed for the pseudo- ray diagram shown below to be true? What kind of lens should the camera be? If you have a choice of different focal lengths within that type of lens, what choices would be better, and why? What kind of lens should the collimator be? If you have a choice of different focal lengths within that type of lens, what choices would be better, and why? gas tubę bluer light redder 982 grating camera collimator lens lens light screen Where should the collimator be placed relative to the light source? Where should the screen be placed relative to the camera?

Answer 1

The collimator makes the rays parallel. So it should be convex lens. The camera also focuses the rays on the screen so the camera lens should be convex. If the focal length of the collimator is larger, then more rays can enter into collimator Then more light rays are made parallel and fall on grating. So, light intensity on screen increases so larger focal length is better. If the camera lens has larger focal length then on screen light intension decreases. So, shorter focal length is better. The position of gas tube is at the focus of collimator lens. The screen also placed at the focus of camera lens