When a beam of white light is allowed to pass through a convex lens parallel to the principal axis, the different colours of light converge at different points on the principal axis after refraction. This is called:
Scattering
Chromatic aberration
Spherical aberration
Polarisation
Correct answer:B
Standard Method
Given: A beam of white light passes through a convex lens parallel to the principal axis, and different colours converge at different points after refraction.
Find: The name of this optical phenomenon.
The refractive index of a lens material depends on wavelength. Hence, different colours of white light refract by different amounts.
Blue light, having shorter wavelength, bends more than red light, having longer wavelength. Therefore, different colours come to focus at different points on the principal axis.
This defect is called chromatic aberration.
Therefore, the correct option is B.
Confusing chromatic aberration with spherical aberration. Spherical aberration is caused by different parts of the same lens focusing differently, whereas here the separation is due to different colours having different wavelengths. Identify whether the variation is with lens zone or with colour.
Choosing scattering because white light is involved. Scattering refers to deviation of light in a medium due to particles, not different focal points after refraction through a lens. Focus on the lens-based image defect described in the question.
Associating the effect with polarisation. Polarisation concerns the direction of oscillation of light waves and does not explain different colours focusing at different axial points. Use wavelength-dependent refraction as the key idea here.
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