5 Things You Should Know About Light

5 Things Every Human Should Know About Light


All of these are electromagnetic waves and they all travel at the same speed (the speed of light). However, they have different interactions with matter. If you are inside, your mobile phone can still get data from a cell tower since these radio waves pass through most walls. Can you see through the walls? No. Visible light does not pass through most walls. X-rays mostly go through your skin, but you can’t see (with visible light) through skin – that would just be weird.

Technically the interaction with light and matter depends on the frequency of light – but since frequency and wavelength are related, we can just talk about the wavelength.

Why Are the Dwarves Seven?

Why Is Snow White?

The whiteness of newly fallen snow is, of course, one of its primary defining characteristics, so it’s tempting to just say that, you know, that’s the way snow is. But it’s actually a pretty good question, because snow is really just frozen water, and frozen water tends to be transparent

The Coin Paradox

The Coin Paradox

A teaser. For the setup, go to the link.

In each case the rolling coin has made one complete rotation. But the red arc at the top is half the length of the red line at the bottom. Why?

I have a more physics-y than a formal math-y explanation of why, which I will post soon.


OK, here’s my answer.

In the rolling case, all you have is rotation. On rotation gives you 2*pi, so it rolls one circumference.

But in the other case you have rotation and revolution (spin and also orbital motion). Going halfway around the coin gives you an equal contribution of each, so the amount of spin only requires pi rotation, and it rolls half of the circumference. If the coin’s point of contact never changed, it would still do a rotation over the course of its revolution. If the orientation stayed fixed, the point of contact would make a complete trip around the coin.

A related example of this is the moon. If viewed from an external inertial frame (where the distant stars appear to be fixed), the moon rotates around the earth every ~4 weeks. But since it’s tidally locked and always has the same part facing the earth, it also rotates once about its axis.


(yay! internet finally restored!)

Why 50 million smart meters still haven’t fixed America’s energy habits

The upshot: Right now, smart meters aren’t waking Americans up and making them conscious of their energy use — because they aren’t being paired with what behavioral research shows us is needed for that to happen.

This is the story of why the smart meter revolution has, thus far, fallen short — and how we can better use one of the most pivotal innovations in the electricity sphere to save energy, cut greenhouse gas emissions and save a lot of money.

I can vouch for the notion of immediate feedback being an important component to changing behavior — something that’s discussed in the article. My new-ish car tells me my instantaneous gas efficiency and reminds me of things that I know but would not necessarily be thinking about, such as how wasteful it is to romp on the gas when speeding up, or how hitting the brakes means you are bleeding away your kinetic energy as heat. So it’s modified how I drive — smaller accelerations. Less gas when speeding up and coasting to slow down, when it’s appropriate to do so. So I can see how this would work for home energy use, too.

Na Na Na Na Na Na Na Na, Boom Boom

Sodium’s explosive secrets revealed

The explosion, say Pavel Jungwirth and his collaborators at the Czech Academy of Sciences in Prague, is not merely a consequence of the ignition of the hydrogen gas that the alkali metals release from water. That may happen eventually, but it begins as something far stranger: a rapid exodus of electrons followed by explosion of the metal driven by electrical repulsion.

Neat. It’s not the hydrogen reacting with air that causes the alkali to explode. That reaction doesn’t cause more surface area to be created as the reaction unfolds, so it can’t “accelerate”

Video in the link, including slow-motion views of the explosion.

It Was Good

Let there be light! Celebrating the theory of electromagnetism

There was also another controversy raging at the time, concerning the nature of light. It was known that light travelled through space with a finite speed, rather than leaping instantaneously from its source to our eyes.

But no-one knew, a century-and-a-half ago, what light was actually made of.

Most physicists agreed it travelled through space as a wave but they didn’t know what these light waves were made of, and they didn’t know how they got from one place to another. Maxwell was about to solve all these mysteries.

Spot Was Observed to Run

How to write your first scientific paper

First advice is to take it seriously. Science isn’t science unless you communicate your results to other people. You don’t just write papers because you need some items on your publication list or your project report, but to tell your colleagues what you have been doing and what are the results. You will have to convince them to spend some time of their life trying to retrace your thoughts, and you should make this as pleasant for them as possible.

Lots of good stuff here. Make sure you know something about the journal to which you are submitting, too. Details vary — this ties in with the “pick a level of discussion and stick with it.”

Bee also mentions that students often write as part of a group. Feedback from colleagues is important and usually makes for a better paper. My advice is drop the ego and be receptive to criticism. And hope that you work with people who will give you honest feedback (a situation I have been fortunate to be in for many years)