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Question
Define the magnifying power of a compound microscope when the final image is formed at infinity. Why must both the objective and the eyepiece of a compound microscope has short focal lengths? Explain.
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Solution
When the final image is formed at infinity.
When the final image is formed at infinity, the angular magnification due to the eyepiece is
me = D/fe
Thus, the total magnification when the image is formed at infinity can be defined as the product of magnification of objective lens and eyepiece. i.e
m = mome = (L/fo) (D/fe)
From the above the equation, we can see that to achieve a large magnification of a small object, the objective and eyepiece should have small focal lengths.
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