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CBSE - XII Science - Physics - Ray Optics and Optical Instruments

Q.On a convex lens ,light of red and violet colour is incident separately , then how does the focal length of lens change?

Asked by Ravi consul 4th March 2015, 6:48 PM
Answered by Expert


If red light and violet is incident on a convex lens, you will observe that red lideviates the least and are brought to a focus at point R. Whereas, the violet rays are deviated the most and are brought to a focus at point V.
From the figure, we can see that the focal lenght of the lens for red colour light (OR) is more than that of violet (OV). Also, the focal lenght depends on the refractive index which depends on the wavelength.Hence, fr > fv
Answered by Expert 11th December 2017, 5:38 PM

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