electron microscopes

[tiger~torah]

i know that an electron microscope has a shorter wavelangth than a light microscope. But why does this make the resolution on an electron microscope better? I'm a bit confused :s

[beso]

A feature can only be imaged by electromagnic waves where the wavelength is shorter than the size of the feature. Longer wavelengths wave right around the object without interacting.

[fo3nix]

Imagine a golf ball. It's a spherical ball, with loads of little pits on the surface.

Imagine you don't know this though, for a second. And to make it easier, imagine that it's really big -- the size of a football or something.

You could take little table tennis balls, and fire them at the big golf ball. You can then measure the angle that it hits the golf ball and bounces off at. By doing this, you can get a picture of what the golf ball looks like. If the table tennis balls are larger than the pits, then their bounce won't really be affected by them, because they'll just be little imperfections to it, so the golf ball with appear spherical after you've used enough tennis balls.

But if you instead use far smaller balls that easily fit inside the pits of the giant golf ball, then if you fire one and it happens to hit inside the pit, it might bounce back at a really weird angle. You'd notice that it wasn't a nice sphere like a football. You'd do this again and again, and it may hit the rim of the pits, etc. Eventually, you'll build up a picture of the golf ball.

So, to see the features of a normal golf ball, you have to use objects that are far smaller than the pits of the golf ball. We can see the pits because the light that we see, made of little particles called photons, are really, really tiny.

Particles adhere to the de Broglie relation, linking momentum to wavelength (which you can think of as the diameter of the particle). So by making the electron go really fast (and have a large momentum), you can make the wavelength really small, helping you to see the little pits and added detail on surfaces.