NEET-XII-Physics
20: dispersion and Spectra
- #5Does focal length of a lens depend on the colour of the light used? Does focal length of a mirror depend on the colour?Ans : Yes, the focal length of a lens depends on the colour of light.
According to lens-maker's formula,
`` \frac{1}{f}=(\mu -1)(\frac{1}{{R}_{1}}-\frac{1}{{R}_{2}})``
Here, f is the focal length, μ is the refractive index, R is the radius of curvature of lens.
The refractive index (μ) depends on the inverse of square of wavelength.
The focal length of a mirror is independent of the colour of light.
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