Which of the following may be used to explain a mirage? I. Layers of air near the road surface have varying…

Analyze the question: A mirage is an optical illusion, commonly seen on hot roads, where a patch of road looks like shiny water. We need to pick which statements explain it.

Concept: On a hot day, the air layer touching the road is much hotter than the air above it. Hot air is less dense, so it has a lower refractive index. This gives layers of air with different refractive indices.

Light from the sky travelling downward passes from the denser (higher refractive index) cool air into less dense (lower refractive index) hot air. It bends away from the normal, and the angle of incidence keeps increasing. Eventually it exceeds the critical angle, and the light undergoes total internal reflection (or is refracted gradually upward). It then reaches the observer's eye as if it came from the road. The observer sees the sky's image on the road, which looks like a pool of water.

Check each statement:

• I. Layers of air near the road surface have varying refractive indices in hot weather. True. This is the basic cause of the mirage.
• II. Road surfaces sometimes become invisible in hot weather. False as an explanation. The road does not become invisible. Instead, an image of the sky appears on it. This is an observation or a wrong description, not the physical cause.
• III. Light from the sky can be refracted upwards after coming close to the road surface. True. This is the bending of light that produces the image.

So the statements that explain a mirage are I and III only.

Answer: A

Tip: For mirage questions, remember the key phrases "varying refractive index" and "light bends or totally reflects upward". Any option that says the road "disappears" is usually a distractor. Also remember that mirages on hot roads are a refraction effect, with total internal reflection at the end of the process.