The Spectrometer

A Spectrometer is an optical device used to study spectra from different sources of light.  

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         For the measurement of properties of light such as the wavelength and intensity, over a particular portion of the electromagnetic spectrum, Spectrometer is used. The field of physics in which spectral lines are produced using a diffraction grating along with the spectrometer in order to examine the spectrum of light is called spectroscopy. The typical spectrometer can be operated over a wide range of wavelengths from γ rays and X-rays to infrared but usually spectrometers are used to study the visible spectrum.

With the help of a spectrometer, the deviation of light by a glass prism and refractive index of the material of the prism can be measured quite accurately. Using diffraction grating, the spectrometer can be employed to measure the wavelength of the light.

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Terrestrial Telescope

As astronomical telescope forms inverted final images of heavenly bodies like moon and stars which are acceptable. But when terrestrial objects are to be viewed, it is necessary to have an erect final image. The erection of image can be made by introducing a third lens between objective and eye-piece of telescope.
This modified telescope is known as "Terrestrial Telescope" whose magnifying power is just equal to the magnification of astronomical telescope but it just gives erect image.  

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      Terrestrial telescope contains three lenses as compared to the astronomical telescope. It is also known as the spyglass. As astronomical telescope forms an inverted image of the object so, the main difference between the astronomical and terrestrial telescope is the erection of the final image with respect to the object. The third lens of short focal length f is placed at 2f which forms inverted image of the object. This image serves as the object for the eye-piece. The lens placed in the center of the telescope which actually erects the image is called as the Erecting lens. The resolving power of the telescope can be given by the relations as follows:

Where,

fo = Focal length of the objective lens

fe = Focal length of the eye-piece lens

f = Focal length of lens placed between objective and eye-piece i.e. Erecting lens

  Ray diagram for Terrestrial Telescope

Images for Terrestrial Telescope