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The focal length of a convex lens is minimum for a) red b) violet c) blue d) green

The focal length of a convex lens is minimum for a) red b) violet c) blue d) green

Grade:upto college level

3 Answers

Saurabh Koranglekar
askIITians Faculty 10335 Points
3 years ago
The focal length is larger for red colour for both convex and concave lenses.High frequency waves, like blue colour, travel the slowest in any given medium, compared to the low frequency waves like red colour. (except for in vacuum, in which they all travel with the same speed).Thus,high frequencywaves like blue colour, bend more (more refraction or more refractive index) compared tolow frequencywaves like red.Thus when incident on a convex (or concave) lens, blue colour would bend more and thus converge (or diverge) closer to the lens. Hence, blue colour would have a shorter focal length, compared to red colour. Thus the focal length of a convex (or concave) lens is maximum for red colour.
Arun
25750 Points
3 years ago
The light with more wavelengths like redrefracts the least and the colour with minimumlike violet wavelength refracts the maximum. There is no relationship between the two as the focal length of a lens is a constant
Vikas TU
14149 Points
3 years ago
 blue colour would have a shorter focal length, compared to red colour. Thus the focal length of a convex (or concave) lens is maximum for red colour.

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