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Himanshu posted an Question
May 28, 2020 • 18:24 pm 30 points
  • IIT JAM
  • Physics (PH)

Optics two lenses of focal length 10cm and 20cm......

Here I am asking two different question Q.1 From pic 1 it's solution and most importantly what is achromatic double???? provide me it's all formula/condition. Q.2 From pic 2&3 here it's obtaining total power of the attached figure but why there is a minus in combined power (highlighted) how sign convention is used there ???

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  • Himanshu Pandey

    Abhishek sir it's answer is given 13.6cm not 15

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    Chandra prakash

    achromatic lens-doublet is formed by placing in contact a convex lens of focal length f1 and a concave lens of focal length f3....... I hope u understood it

    eduncle-logo-app

    f3* ...replace by f2.

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    Abhishek singh best-answer

    For your first doubt. Achromatic double means, combination of two lenses such that the chromatic Aberration is removed. and it's condition is attached alongwith. Do read this comment and follow the attached. Best regards.

    eduncle-logo-app

    this method has already been discussed in one of your previous doubts. They have changed the language of question. But they have asked the same concept.

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    Abhishek singh Best Answer

    Solution for second part of your question. Do ask doubts if any. actually powers are always add when lenses are in contact. but here the power itself is negative for Plano concave lens. that's why there is a negative sign. Best regards.

    cropped8956732998023180629.jpg
    eduncle-logo-app

    do remember these methods of solving questions.

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    Ruby negi

    ohmega 1 and omega 2 in last page is dispersive power of lens 1 and lens 2.

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    Dhairya sharma

    dear in second question..... as we know total power should be sum of power of both lenses but it's negative due to direction of their focus distance. and the factor of two must be here due to some condition given in question.

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