Which of the following is not due to the refraction of light?

Correct option is C

The correct answer is (C) Image formation by a convex mirror

Explanation:
• Refraction is the bending of light when it passes from one transparent medium to another with a different optical density.
• A mirror, however, whether plane, concave, or convex, operates purely on the principle of reflection (the bouncing back of light from an opaque, polished surface).
• Therefore, the image formation by a convex mirror (like the rear-view mirror of a car) is entirely due to reflection, not refraction.

Information Booster:
• Convex Mirror Properties: A convex mirror always forms an image that is virtual, erect, and diminished (smaller than the object), allowing it to provide a wider field of view for drivers.
• Atmospheric Refraction: The Earth's atmosphere has layers of varying densities and temperatures. As starlight passes through these shifting layers, it refracts repeatedly, causing the star's apparent position and brightness to flicker—this is the twinkling effect.

Additional Knowledge:
• Option A (Twinkling of stars): Caused by atmospheric refraction as light travels through turbulent air layers.
• Option B (Delayed sunset/Early sunrise): Atmospheric refraction bends sunlight coming from below the horizon, making the sun visible for about 2 minutes before actual sunrise and 2 minutes after actual sunset.
• Option D (Convex lens): Lenses are made of transparent glass. They form images exclusively by refracting (bending) the light rays that pass through them.