Karnataka Board PUCPUC Science 2nd PUC Class 12

Does Focal Length of a Lens Depend on the Colour of the Light Used? Does Focal Length of a Mirror Depend on the Colour? - Physics

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Short Note

Does focal length of a lens depend on the colour of the light used? Does focal length of a mirror depend on the colour?

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Solution

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.

Concept: Lenses
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Chapter 20: Dispersion and Spectra - Short Answers [Page 441]

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HC Verma Class 11, Class 12 Concepts of Physics Vol. 1
Chapter 20 Dispersion and Spectra
Short Answers | Q 5 | Page 441

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  2. A spherical air bubble is embedded in a piece of glass. For a ray of light passing through the bubble, it behaves like a ______.
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    (b) diverging lens
    (c) mirror
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  4. The magnification of an image by a convex lens is positive only when the object is placed ______.
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  4. Write an expression for magnifying power of a compound microscope when its final image lies at the least distance of distinct vision (D).
  5. State any one difference between a reflecting telescope and a refracting telescope.

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