A white light is falling on a bi-convex lens. | vedclass

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(B) The focal length $f$ of a lens is given by the Lens Maker's formula: $\frac{1}{f} = (\mu - 1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right)$.Accord

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(B) The focal length $f$ of a lens is given by the Lens Maker's formula: $\frac{1}{f} = (\mu - 1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right)$.According to Cauchy's formula,the refractive index $\mu$ is related to the wavelength $\lambda$ as $\mu = a + \frac{b}{\lambda^2}$.For white light,the wavelengths follow the order $\lambda_V Since $\mu$ is inversely proportional to $\lambda^2$,we have $\mu_V > \mu_R$.Substituting this into the lens formula,since $\frac{1}{f} \propto (\mu - 1)$,we get $f_V This means the focal length for violet light is smaller than the focal length for red light.Therefore,the violet light focuses closer to the lens than the red light,which corresponds to the behavior shown in option $(B)$ of the provided images.

$A$ white light is falling on a bi-convex lens. Which of the following options represents the correct qualitative behaviour of the focussing of this light?

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