Saturday, 11 May 2013

Bad Physics: No Energy Radio Waves

Just a little bit of Bad Physics, this time from the L. A. Times. The story was "Mysterious hydrogen clouds detected in space, puzzling scientists", a nice story.
I quote
"The clouds don't emit light or energy, but the neutral atomic hydrogen that they are made of gives off a distinct radio signal that astronomers were able to pick up using the National Science Foundation's Green Bank Telescope which measures radio waves."
Apparently, these clouds do not emit light or energy, but they do emit radio waves that we can detect with out telescopes. Aghhh!!

I know that you already know this, but radio waves are one form of electromagnetic radiation, and (in terms of quantum mechanics) are packets of energy called photons. The energy of a photon is given by
where λ is the wavelength of the radiation.

Light has a wavelength of around 550nm, and so each photon carries some energy. Radio waves, however, have wavelengths from millimetres to many hundreds of kilometres. Such long wavelengths mean each photon carries a much smaller amount of energy, but they still carry energy!

2 comments:

  1. Do you like to use the term "light" to mean any kind of electromagnetic wave? I do. Radio waves are just really long wavelength light. It's the same phenomenon, so we may as well give it the same name.

    Anyway, more importantly, I'd love to see a rant post on the following topic: why the hell do people call infrared light "heat"? ARGH! IT DRIVES ME MAD!

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    Replies
    1. Light is a tricky one, but I am like you - I use light to basically cover all over the electromagnetic spectrum - and optical for that bit which we see. But the important thing is to remember is that there are no rigid boundaries for optical verses IR, or UV or radio or X-ray. And even optical is not well defined; clearly there are animals that see more of the solar spectrum than we can (and I wish I was a mantis shrimp to **really* see colours http://theoatmeal.com/comics/mantis_shrimp).

      As for IR being called heat - isn't that because it feels hot (and hot = heat :)

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