If focal lengths of a convex lens for red and violet lights are $f_r$ and $f_v$ respectively, then:

i) $f_r = f_v$
ii) $f_v

Question

If focal lengths of a convex lens for red and violet lights are $f_r$ and $f_v$ respectively, then:

i) $f_r = f_v$
ii) $f_v < f_r$
iii) $f_r < f_v$
iv) $f_v \geq f_r$

Accepted Answer

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> [!TLDR]
> Violet light has a larger refractive index than red, so a convex lens has a shorter focal length for violet: $f_v<f_r$.
>
> By the lens-maker's relation $\dfrac{1}{f}=(n-1)\left(\dfrac{1}{R_1}-\dfrac{1}{R_2}\right)$, focal length decreases as $n$ increases. Since $n_{violet}>n_{red}$, we …

Q.If focal lengths of a convex lens for red and violet lights are $f_r$ and $f_v$ respectively, then:

Concept understanding — Dispersion by a Prism

Dispersion by a Prism – First Principles

The core idea: refractive index depends on colour

The precise statement

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Q.If focal lengths of a convex lens for red and violet lights are frf_rfr​ and fvf_vfv​ respectively, then:

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Q.If focal lengths of a convex lens for red and violet lights are $f_r$ and $f_v$ respectively, then:

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