Saturday, May 24, 2003
M I N D  G A M E S

Planck’s lamp
Aditya Rishi

Sir Joseph John Thomson (1856-1940) was awarded the Nobel Prize for Physics in 1906 having proved that electrons (consequently, light) are particles. 31 years later, his son, Sir George Paget Thomson (1892-1975) was awarded the Nobel Prize for proving that electrons are waves. They were both right.

1906: Joseph John Thomson, Cavendish Professor of Experimental Physics at Cambridge, where he succeeded the great Lord Rayleigh, is having celebrations at home. His work, ‘Conduction of Electricity through Gases’, published in 1903 and described by Lord Rayleigh as a review of "Thomson’s great days at the Cavendish Laboratory", has won him the Nobel Prize for Physics. He has a firm belief that his theories cannot be challenged.

His son, 14-year-old George, is, however, not like his father. The buzz is that he has, so far, shown no sign of being a future scientist. "I have done experiments with light, but I see nothing but darkness when I look into my son’s future," says Joseph John Thomson to his guests at the party. "Good heavens, Thomson! Surely, Master George has some talent that you haven’t spotted," says Lord Rayleigh.


"He only likes to play silly games. I have tried all ways to make him start taking interest in science, but failed every time," says the Nobel Laureate. "Have you tried playing games with him?" says Max Planck, who is also a Nobel Laureate. It is surely a distinguished gathering. "What games?" says Joseph John. "Let me demonstrate. Please, call your son, he hasn’t seen my house," says Planck.

Planck (to the boy after he’s brought): "A light bulb hangs in my room across the street and, outside, there are three switches, of which, only one is connected to the lamp. Right now, all switches are ‘off’ and the bulb is not lit. Let’s play a game. You are allowed to check in the room only once to see if the bulb is lit or not. This is not visible from the outside. Find out with which of the three switches the light bulb can be switched on." The guests follow George to Planck’s house.

To find the correct switch (1, 2, or 3), George turns switch 1 to ‘on’ and leaves it like that for a few minutes. After that, he turns switch 1 back to ‘off’ and turns switch 2 to ‘on’. Now, he enters the room. If the light bulb is lit, he’ll know that switch 2 is connected to it. The bulb is not lit, so, it has to be switch 1 or 3. He touches for short the light bulb. If the bulb is still hot, then, switch 1 was the correct one; the bulb is cold, so, it has to be switch 3. The guests: "Good heavens, Thomson! The child’s a genius." J.J. Thomson: "Gentlemen, I apologise for hiding the truth, but if I ever recommended his name for a Cambridge fellowship, I didn’t want anyone to say that he didn’t deserve it." (Write at The Tribune or