Assertion -Two convex lenses of same material and equal focal length -f - from achromatic combination when separated by distance -f - Reason- 1F-1f1-1f2-df1f2 where F- equivalent focal length of lenses having focal lengths f1 and f2 separated by a distance -d -

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Assertion :Tw...

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Assertion :Two convex lenses of same material and equal focal length $^{'} f^{'}$ from achromatic combination when separated by distance $^{'} f^{'}$ . Reason: $\frac{1}{F} = \frac{1}{f_{1}} + \frac{1}{f_{2}} - \frac{d}{f_{1} f_{2}}$ where $F =$ equivalent focal length of lenses having focal lengths $f_{1}$ and $f_{2}$ separated by a distance $^{'} d^{'}$

Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

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Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

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Assertion is correct but Reason is incorrect

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Both Assertion and Reason are incorrect

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Solution

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
For achromatic combination of two convex lenses of same material separated by distance $x$ such that,
$\frac{ω}{f_{1}} + \frac{ω}{f_{2}} = \frac{2 x ω}{f_{1} f_{2}}$
Hence the Reason is not the correct explanation for Assertion.

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Assertion :Two convex lenses of same material and equal focal length ′f ′ from achromatic combination when separated by distance ′f ′. Reason: 1F=1f1+1f2−df1f2 where F= equivalent focal length of lenses having focal lengths f1 and f2 separated by a distance ′d ′

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for AssertionFor achromatic combination of two convex lenses of same material separated by distance x such that,ωf1+ωf2=2xωf1f2Hence the Reason is not the correct explanation for Assertion.