Question: Assertion (A) : In a reflecting telescope, the image does not have chromatic aberration. Reason (R) : Chromatic aberration occurs only due to refraction of light through an optical medium.

Step 1 (Governing Principle): [0.25 Mark]
Chromatic aberration is an optical defect caused by the dispersion of light. It occurs because the refractive index ($\mu$) of a lens material depends on the wavelength ($\lambda$) of light, leading to different focal lengths for different colors: $$f \propto \frac{1}{(\mu - 1)}$$

Step 2 (Logical Deduction): [0.5 Mark]

• Assertion (A): Reflecting telescopes use concave mirrors as objective elements. Since the law of reflection ($\angle i = \angle r$) is independent of the wavelength of light, all colors focus at the same point. Thus, reflecting telescopes are free from chromatic aberration.
• Reason (R): Chromatic aberration is fundamentally a property of refractive elements (lenses) where the medium's dispersion causes light to split. Mirrors do not involve refraction; hence, they do not exhibit this defect.

Step 3 (Final Concluded Answer): [0.25 Mark]
Correct Option: Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).

💡 EL10 Concept Insight: Think of a lens like a prism that accidentally bends different colors of light by different amounts, making the image look blurry or rainbow-edged. A mirror doesn't care about color—it just bounces all light off its surface at the exact same angle, keeping the image sharp and clear!