When blue light is used instead of red light | vedclass

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(B) According to the Lens Maker's Formula: $\frac{1}{f} = (n - 1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right)$.Here,$n$ is the refractive index of th

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decrease

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(B) According to the Lens Maker's Formula: $\frac{1}{f} = (n - 1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right)$.Here,$n$ is the refractive index of the lens material.According to Cauchy's equation,the refractive index $n$ is inversely proportional to the square of the wavelength $\lambda$ $(n \propto \frac{1}{\lambda^2})$.The wavelength of blue light $(\lambda_b)$ is smaller than the wavelength of red light $(\lambda_r)$.Therefore,the refractive index for blue light $(n_b)$ is greater than the refractive index for red light $(n_r)$.Since $\frac{1}{f} \propto (n - 1)$,a higher refractive index results in a larger value of $\frac{1}{f}$,which means a smaller focal length $f$.Thus,when blue light is used,the focal length of the convex lens decreases.

When blue light is used instead of red light in a convex lens,its focal length will ......... .

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