Question

How can the chromatic aberration be corrected?
(A) By providing different suitable curvature to its two surface
(B) By combining it with another lens of opposite nature
(C) By reducing its aperture
(D) By providing proper polishing of its two surfaces

Answer 1

Hint: Recall why the chromatic aberration occurs in the lens? Recall the dependence of focal length of lens on the wavelength of light. To remove the chromatic aberration, the aberration produced by one lens should be eliminated by the other lens.

Complete answer:
To answer this question, we have to explain what chromatic aberration is. It is the change in the position of the image due to change in wavelength of light. We know that the refractive index of the glass depends upon the wavelength, \[\mu = \dfrac{{{\lambda _0}}}{\lambda }\], where, \[\mu \] is the refractive index,\[{\lambda _0}\] is the wavelength of light in vacuum and \[\lambda \] is the wavelength of light where we have placed the lens. Therefore, if the refractive index varies with wavelength, then the focal length, image distance and object distance also varies with the wavelength.We see the chromatic aberration can be removed by using two different lenses of opposite nature. The dispersion produced by the first lens can be removed by the second lens if placed properly. In that case, the first lens produces low dispersion which can be removed by the second lens that produces high dispersion. Therefore, the chromatic aberration can be eliminated by combining it with another lens of opposite nature.
The chromatic aberrations cannot be removed by providing suitable curvature to the both surfaces of the lens or by reducing the aperture. Also, by polishing the lens, only the image will be cleared but the chromatic aberrations cannot be removed. Therefore, the options (A), (C) and (D) are incorrect.

So, the correct answer is option (B).

Note: When the light passes through a certain glass, it undergoes dispersion and the red and blue light refracts through the lens. Since the red and blue light undergo the deviation at different angles, they focus at two different points and therefore, the image gets distorted.