Thesis: Delhi Metro Might Be a PN Junction Diode

Fever does amazing things to you. An empty mind is the Devil’s workshop they say. And lying on the couch, doing nothing can generate many thoughts in the head. Some make sense, some may not, but I will share them all anyway.

I have been travelling in the metro since a long time now, courtesy my house being situated in between two different lines; The Red and The Yellow. The Red line was the first to start and the Yellow the next, so I can say that I have been using the Metro since it first arrived in Delhi. This has given me an ample time to observe.

A p-n junction in thermal equilibrium with zer...

Image via Wikipedia

I know, a lot has been said about the different kinds of people who travel by the metro. They have been categorised into different categories. There are those who talk loud over the phone. Making sure that everyone within a 500 meter radius knows, that a delivery of 10 cartons has

to made by 3 PM to a store in Gurgaon and that his wife will be going to her parents and has made dinner and has kept it in the fridge. Those who play music loud, despite there being a constant announcement over the speakers, that music should not be played inside. And then there are people who sit on the floor of the metro despite warnings from the aforementioned speakers. But aren’t such people everywhere.

Now, who hasn’t had had an experience with the sudden ringing of a cell phone in the cinema hall, when an important twist in the movie was coming up. So, I won’t talk about these people. But I will address a more important question, that has been bothering me since some time

Is The Metro One Big Junction Diode?

For the less educated ones, a diode is a two terminal device. It is made by joining two semi-conducting pieces, one with excess of positive particles called the P side and the other with excess of negative particles and is called the N side. The place at which the two sides are joined is called the PN junction. It is a gate where the majority charge carriers are concentrated, attempting to cross over to the other side. And they form a sought of a barrier that increases as the current across the diode increases. Opposites attract, that is the universal law.

So where is the similarity?

Basic Assumptions

Even at 0A current supply there is a slight voltage reading

Those who have travelled by the Metro, might have noticed that the area right in front of the door tends to have the highest density of human population. Both inside and outside the Metro. Let us assume the people inside as the Positive charge carriers and the ones outside as the Negative charge carriers. That

means that the door can be safely considered to the be junction across which the transfer of charge will take place.

No Load Current

At no load, that is when no current is being transferred across the diode, there still is a small barrier around the gate. In a real diode, this can be observes via a multimeter that gives a small reading of voltage. In the metro we can observe this phenomenon using our visual senses. Most of the particles inside the Metro have an affinity to stay close to the junction gate. Even though, the train would be moving and the station a good 5 minutes away. They refuse to move inside towards the more open space.

The Negative Particles Remain in Line at No Load

Outside the metro, i.e. on the platform, the Negative carriers station themselves in anticipation. Though the gate is not present, but somehow the particles have a sixth sense of knowing where the gate will arrive (the notification that tells you where the door will be, also helps). Let us call it an invisible gate, or say that though the gate is not present, there still remains some positive charge over that spot to attract them. The usually stay in a line, guided by a few neutral particles wearing the Metro Dress.

Load Characteristics

As the current is passed, the majority carriers start crossing over the other side. The barrier increases which restricts the flow of particles. But as the current is further increased, the barrier breaks down and the diode starts conducting heavily.

The current equivalent for the metro is the arrival of the train on the station. As the train nears the station, the barrier grows. The negative ions outside,

On the verge of a Junction Barrier Breakdown

which were aligned in an orderly fashion also begin to move around in a haphazard direction. As the charges attempt to cross over, clashes occur due to barrier opposition from both side. Sometimes a flurry of abuses can be heard. Usually in different languages. As the junction barrier breaks down, the particles on both sides, rush to the other side. The force of the charged particles can best be compared with a Tsunami. And if you are caught in this wave…well may god have mercy on your soul. Unlike a real diode the the bias does not effect the working here.


With the above points, I have tried to prove that the Metro is nothing but a big PN junction diode with multiple gates, parallel to each other.

Foreign Particles were also observed

Is it or is it not? That I leave to you guys to decide

Did I make sense? Did I not? No don’t think too much on that. I write this piece as my head spins with fever.

22 Responses to “Thesis: Delhi Metro Might Be a PN Junction Diode”
  1. +1 Patty…pretty good observation if I do say so myself.

  2. tangyorangesour says:


  3. Pzes says:

    Wait. Woah!! 🙂

  4. Prateek says:

    Epic. I blogged on the observation in Metro but this is more like a Semi-conductor.
    Can I also saw Metro is a Zener Diode, reverse bias does the trick here too (pun).

  5. Purbaray says:

    I see…. the electric currents have played havoc with your brain. And we can safely conclude that the Metro is fully charged.

  6. LOL
    It indeed is a nice comparison. But what about the reverse bias? Your post on a junction diode makes me think of rewriting a post that I had thought of but left out of procrastination. Perhaps, in due time.

    Nice witty post.

    Blasphemous Aesthete

  7. “For the less educated ones”
    So if we don’t know what a PN junction diode is we’re illiterate?

  8. Mayank says:

    Interesting observation prateek. I had all but forgotten PN diodes – thanks to you for refresher. Made me wonder what analogy will hold true for mumbai locals. Where the junction is always broken. The people standing in line was nice – never knew, delhizens have started doing a la singapore.

  9. Sapna says:

    ha ha nice esp liked the caption “Foreign particles”.

    P.S: Get Well soon 🙂

  10. Deboshree says:

    I am very intrigued by this elaborate thesis. The fever seems to be very productive if you don’t mind my saying that. 😀

  11. what course are you in snow leopard???

    Im a planner(urban &environmental)….and i have done some studies in my masters years myself….so this is an interesting read…

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  1. […] Posted by snowleopard on August 15, 2012 · Leave a Comment  Made this comic for an event in the college. You might also like to check the “Thesis” I had written on the Delhi Metro by clicking on this link – Thesis: Delhi Metro Might be a PN Junction Diode […]

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