15 year olds
When I graduated from standard 7 to standard 8 we had a new teacher to teach us Physics. I still remember her name was Kalpana. We used to call her “Kalpana Miss”. She taught very well. She answered every question honestly. She made sure you understood it. She encouraged asking questions. What was more she loved me. I was the most mischievous of the whole class. But I was never punished. I was also the guy who asked the most questions. And also the guy who paid he most attention to every concept. But only till I understood it.
We had a great time in her class. She had a knack of covering a lot of concepts rapidly. But her classes never seemed cluttered or hurried. Probably because she herself understood the subject with clarity. And whatever she could not answer, she asked us to discuss with her after the class.
I still remember one topic very well. We were studying REFRACTION. Why mirages occur in deserts? It was optics again. She explained that land on the deserts gets heated up very rapidly and starts heating up the air above. Since air is a bad conductor of heat, it is a little sloppy in transferring the same heat to the air lying above it. Hence the lower layers of air, the ones closer to the land, were always hotter than the ones above. Due to irregular expansion under these differential temperature conditions, different layers of air would develop different mass densities. And hence different optical densities as well.
When blue light entered these layers from from the sky, it would skew a little and bend away from its normal course. Every time it entered a new density layer, it would skew a little more. After a series of continual bending, it would finally start moving upwards away from the ground.
That was cool! Light bends so much due to refraction, that it starts moving upwards after it has suffered enough refraction. It never hits the sand at all. So it can’t have the color of sand. It still has the color of the sky. Blue. And when such light enters our eyes, we see it as blue light coming from the land. It looks like water. That is a mirage.
I was listening intently. And as soon as she finished, I jumped with a question.
“Light only skews away from the normal when it is enters a layer of different optical density. But onces, the light is skewed enough that it is almost horizontal to the ground, it has no differential optical densities to cross. So it should just move horizontal. Why does it move upwards?” I said. Now that was a big sounding question. Immediately the class lost interest. But I was persistent. She tried to convince me that that is how it is. But I never gave in. I went on arguing.
“Light bends so much due to refraction, that it starts moving upwards after sometime” she said again. “But light has no reason to skew anymore once it is completely horizontal. It doesn’t cross any optical differentials anymore. So it should NOT bend upwards.”
This was clearly a dent in her argument. So a few boys took notice that maybe I was serious about this. And maybe I was even right. So another guy stood up. His name was Siddharth. He tried to explain me what the teacher was saying. But I insisted that it doesn’t break my argument. After sometime another guy stood up. His name was Anindo. He was a very cool headed guy. He also said something about the problem at hand. And we all got into an argument. Siddharth and Anindo on one side, and me on another. We were defending our own point of views like professors who were involved in a big debate. It felt like we were working on something very important. We wracked our brains very hard. We gave it everything we had. We were 15 years old.
Anindo finally said, “I don’t think we can say anything against Abhishek’s argument.”
And the argument ended abruptly. We all understood that we don’t understand this completely. We all agreed that the argument is given in the book was flawed.
I wonder now, how it must have felt then. I had put the whole class against me. I did not care what they thought. I argued with my teachers if I felt they were wrong. I never gave in until I understood and agreed with them. When I was 15, I had a lot of courage and confidence. I trusted my head.
Years later when I was discussing the same with my friend, he pointed out that the reversal of direction of light was because of what we called Total Internal Reflection and was not just a case of ordinary refraction. Then it all fit into place.