Physics Problem

Kevin Drum posts the following:

Over the past couple of weeks, I've noticed that my distance vision is a little fuzzy. Time for new glasses, you say, and you're probably right. But here's the odd thing. I keep all my old glasses, and last night I tried them all on just to see if an older prescription worked better than my current glasses. What I discovered was a little strange.

Right under my TV I happen to have two LED clocks. One uses red LEDs and the other uses blue LEDs. With my current glasses, the blue LEDs are sharp and the red LEDs are fuzzy. But when I put on glasses that are a few years old, it changes. The red LEDs are sharp and the blue LEDs are fuzzy. The difference is quite noticeable, not a subtle thing at all.

Anyone know what this is all about?

Naturally some of his commenters got the correct answer, but you should try to solve it without looking (zillions got wrong answers, of course). Hint: there are two parts to the answer, one involving physics, the other involving physiology.

UPDATE/Solution: OK, since only one person ventured this, and not really successfully. The eye is not an achromatic lens. Red and blue focus at different distances. Young people don't notice this since their eyes automatically adjust by slightly changing the focus of the lens of the eye. Old people, with stiff, inflexible lenses, can't do this.

Comments

Post a Comment

Popular posts from this blog

Anti-Libertarian: re-post

The most pointed critique of social security and liberalism in general is the libertarian critique. The problem with libertarians, for a liberal, is that we have too much in common. We both believe in individual rights, tolerance of individual differences, and dislike government prescription of religion. The basic difference, it seems to me, is the different answers we give to Cain's (with thanks to the Captain - my original version had the corpse asking the question!) famous question: "Am I my brother's keeper?" That's not really my basic bitch against the libertarians though. My real complaint is the same as my complaint against most religion - its premise is a fraud. For those who can't stand to wait for the punchline, I believe that trying to implement libertarian principles leads to tyranny or social disintegration. Demonstrating that takes some historical (and pre-historical) context. For all but the last 15,000 or so of the 100,000 years the human spec
Read more

Uneasy Lies The Head

Uneasy lies the head that wears a crown ........... Shakespeare Henry IV, Part II. So it is with us and our slightly distant primate cousins , so it seems. A 9-year study of wild baboons in Kenya by Princeton University and the Institute of Primate Research may turn conventional assumptions of alphas males upside down. The study found that alpha males have high testosterone levels, which allows them to dominate other baboons, get access to more food, and attract better mates. This is expected. Surprisingly, though, the alpha males also have high levels of stress hormone glucocorticoid, which scientists measured from their feces samples. In fact, the stress of alpha baboons was on par with low-ranking baboons. The convention wisdom is that access to food and females provides life security and thus less stress for dominant males. Conversely, weak males who are constantly threatened by starvation and physical violence from stronger males are thought to be more stressed. The st
Read more

We Call it Soccer

The US played its best, and maybe only good game of World Cup, but lost thanks to brilliant goalkeeping by the Swedish keeper and the bizarre method soccer uses to settle ties when three US stars could not put the ball on frame from the 12 yard spot.  At the end it came down to a blocked shot that spun in by maybe a couple of centimeters. Well, that's football - too much like life.   Which brings me to a modest proposal.  Replace the thirty minute overtimes with as many 7-player 15 minute periods as needed to settle it.  Scoring should be much easier with fewer players.
Read more