JAMB 2015 Physics · Question 23

A motor boy of a driver saw what seems to appear to be a pool of water a head of him, while his driver drives…

Question

A motor boy of a driver saw what seems to appear to be a pool of water a head of him, while his driver drives a new truck on a sunny day. Which of the following explains his observation?

A.He saw a flying objects
B.He must be thinking of water and food
C.He was seeing the shadow of the car
D.The sun ray from the sky were passing from a hot air (layer) to cold layer

Answer: D. The sun ray from the sky were passing from a hot air (layer) to cold layer

Explanation written with AI and checked against the answer key

Analysis of the Question

This question tests your understanding of Optics, specifically the phenomenon of Refraction and Total Internal Reflection as they relate to atmospheric conditions. The observation described is a classic example of a mirage.

Explanation of the Concept

A mirage occurs on hot, sunny days when the air near the ground becomes significantly hotter (and therefore less dense) than the air higher up.

Temperature Gradient: As the sun heats the road surface, the layer of air immediately above the road becomes very hot. The air layers above that remain cooler and denser.
Refraction: Light rays from the sky travel from the cooler, denser air into the hotter, less dense air. According to Snell's Law, when light travels from a denser medium to a less dense medium, it bends away from the normal.
Total Internal Reflection: As the light rays continue to bend away from the normal, they eventually hit the hot air layer at an angle greater than the critical angle. At this point, the light undergoes Total Internal Reflection and is reflected upwards toward the observer's eye.
The Illusion: The observer's brain assumes light travels in a straight line. When the reflected light reaches the eye, the brain traces it back to the ground, creating the illusion of a shimmering pool of water (which is actually just an image of the blue sky).

Step-by-Step Solution

Step 1: Identify the phenomenon. The "pool of water" on a hot road is a mirage.
Step 2: Evaluate the physics. Mirages are caused by the variation in the refractive index of air due to temperature differences.
Step 3: Analyze the options. • A, B, and C are psychological or incorrect physical explanations. • D describes the transition of light through air layers of different temperatures (densities), which is the fundamental cause of the refraction and reflection that creates the mirage.

Conclusion

While the phrasing in option D ("passing from a hot air to cold layer") is a simplified way of describing the temperature gradient, it correctly identifies that the phenomenon is caused by light passing through air layers of different temperatures.

Exam Tip: Whenever you see a question about a "mirage," "shimmering road," or "oases in the desert," always look for keywords like refraction, total internal reflection, or temperature gradient. These are the physics principles that govern these illusions!

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