We combined a convex lens of focal length f_1 | vedclass

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(A) For a combination of two thin lenses in contact,the equivalent focal length $F$ is given by the formula: $\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f

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$f_1 > f_2$

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(A) For a combination of two thin lenses in contact,the equivalent focal length $F$ is given by the formula: $\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2}$.Here,$f_1$ is the focal length of the convex lens (positive,so $f_1 > 0$) and $f_2$ is the focal length of the concave lens (negative,so let $f_2 = -|f_2|$).Substituting these,we get: $\frac{1}{F} = \frac{1}{f_1} - \frac{1}{|f_2|} = \frac{|f_2| - f_1}{f_1 |f_2|}$.Thus,$F = \frac{f_1 |f_2|}{|f_2| - f_1}$.For the combination to behave like a concave lens,the equivalent focal length $F$ must be negative.This occurs when the denominator $|f_2| - f_1  |f_2|$.Therefore,the combination behaves like a concave lens if $f_1 > f_2$ (where $f_2$ represents the magnitude of the focal length).

We combined a convex lens of focal length $f_1$ and a concave lens of focal length $f_2$. Their combined focal length is $F$. The combination of these lenses will behave like a concave lens if:

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