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Explain the working of an astronomical telescope using refraction of light.
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The astronomical telescope consists of two lenses: objective and eyepiece. Objective has larger focal length and diameter to accommodate maximum amount of light coming from the far away (astronomical) objects.

Working :

  • A parallel beam of rays from an astronomical object is made to fall on the objective lens of the telescope.

  • It forms a real, inverted and diminished image A'B' of the object.

  • The eyepiece is so adjusted that A'B' lies just at the focus of the eye piece.

  • Therefore, a highly magnified image of the object is formed at infinity.

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