Story-I: The Great Expectations-2

contd...

Leaning back on the bench, Pip tried to relax. A thin film of oil floating on water, reflecting the colors of rainbow, caught his attention. ‘Thin-film interference’ he thought to himself. His thoughts rolled back to his 9th standard.


“How is a rainbow formed? Who will explain?”
One arm raised.
“Yes Pip” said the Science Sir simultaneously gesturing with his hand.

“When sunlight passes through raindrops, it splits into various colors. L..Like the prism” Pip finished with slight stammering at the end. Apparently his interest in solving physics puzzles from weekly magazines helped him to know the answer.

“Good. That is what it is in brief” Sir continued. “White light, which is nothing but the light you see, is a bunch of spectrum of various colors. Again, spectrum is nothing but a range of wavelengths. Each color in the spectrum has different wavelength. For example, Red light has a wavelength of 700nm and violet has a wavelength of 400nm. One should note here that when I say Red is at 700nm, it doesn’t mean that it is at 700nm only. There are also other shades of red near 700nm. This is why we see a band of red in the rainbow and not a single line. Same thing applies to all other colors too.” He paused a moment and continued. “When the white light passes through prism, it undergoes refraction. We have seen earlier, from Snell’s Law, that the angle of refraction directly depends on the wavelength.” He paused again and looked at the class. “Joseph! Stand-up and tell what is Snell’s Law”. He almost shouted resting his tired bum on the class table.

Joseph was scribbling something. Apparently he is sketching another film poster. Ever since he watched ‘Titanic’, he developed a fantasy in sketching. Although not as good as ‘Jack Dawson’, he is not bad at it and has been improving. He dropped his pen suddenly on the table and stood up. All heads towards him now.

“Yes, What is Snell’s Law?” Questioned the Sir again.
Joseph just stood silently with what is called a ‘blank-face’.

“Next” came a firm voice from Sir after giving ample time to Joseph.
Then stood the all famous Abdul-Jabbar-Khan. Famed for his great grand name and the often sheepish laugh which he carried all the way all the time. His face can never be ‘blank!’ So he stood up with a huge grin with all sorts of shy and ‘trying-hard-to-control’ emotions. That was good enough for the class to burst in to laughter. Not even the Sir could hide it from class.

“Who will answer this?” he finally gave up on the row and looked up for some soothing from someone in the class. About 8 to 10 hands were in the air. That seemed to be a good relief to him in a class of 40 odd.

“Rohan, come to the board and write the equation” he said picking Rohan from the hands raised and offering him the chalk piece.
Rohan went to the board and wrote the equation:
Sin(θ1)/Sin(θ2) = v1/v2 = λ1/λ2 = n2/n1.


He then returned the chalk to Sir and went back to his seat.


“So this is Snell’s Law” Continued Sir. “This also shows that waves of different wavelength bend at different angles at the refracting surface. Since we have seen that there are lights or colors of different wavelengths in the white light, they are bent at different angles at the surface of the prism. This results in the split and thereby we see a spectrum of colors. In the case of a rainbow, the water drops falling from clouds act as natural prisms to the sunlight. This phenomenon is called dispersion.” Sir stopped there for a moment. “Any questions?” he asked the class.


“Sometimes when it rains we see thin films of oil on water reflecting rainbow colors. Is this too due to the same reason?” Sasha’s voice echoed softly from the girl’s corner. Sasha is a petite gal with more number of questions than neurons in her brain. She was often called ‘puppy’ for her continuous howling.


“No. That is a totally different concept. It is due to interference of the light being reflected from the top and bottom surfaces of the oil above the water. Dispersion plays its role here too but it’s not the main reason. You can understand it much better after I finish the concepts of phase and interference. I will explain then.” Sir responded. And Sasha noted it down for future use. She doesn’t miss any of those ‘Shasha-Questions’. That’s what they were called.


“Excuse me, Sir” It was the head master with the P.E.T and 4 guys from the 10th standard. Apparently they are the new ‘House-Leaders’ of the school and now it would be the division of houses namely, blue; yellow; green; red. They have already picked the Assistant-House-Leaders, 4 gals for 4 houses from the penultimate standard, and Rachel is the Assistant-House-Leader for Blue House. Pip would be the House-Leader of a House at class level. He is anxiously waiting. He wants it to be the Blue House for him.

The vibration of his cell phone woke up Pip from his retrospect. He unlocked it to see the message.
“Wru” from Rachel.
“In d park… Waiting fr u…” He replied.
“Im stuck up wid smthn. Wll b thr in hf hr” The response was spot-on.

to be contd...