10.01.2007

Let's learn about light!

[UPDATE]: Spectroscope build instructions delayed until I fix whatever the hell is wrong with my digital camera. Sorry :\

This weekend I was blessed with a dearth of homework, so I decided to build two types of spectrometer from more-or-less useless items found around my bedroom. But before we get to the fun part (building), we need to learn some science-y shit first.

Electromagnetic Energy

What we commonly refer to as "light" is actually a type of electromagnetic radiation that is visible to the eye (note: radiation means the exchange of energy between bodies which need not be in physical contact). The electromagnetic spectrum includes radio waves, microwaves (actually a type of radio wave),infrared radiation, visible light, ultaviolet light, x-rays, and gamma rays. Electromagnetic radiation travels in waves (though it also exhibits characteristics of a particle, we will not be dealing with that aspect here). Below is a diagram of a wave with it's parts labeled (click images for full version).


Electromagnetic energy at a particular wavelength λ (in vacuum) has an associated frequency f and photon energy E. Therefore, the electromagnetic spectrum can be expressed in terms of these three qualities:
wave speed (c) = frequency x wavelength
λ = c/f
E = h/f
E = (hc)/λ
Where:
c = The constant of light 299,792,458 m/s (exact)
h = Planck's constant 1.05 *10 -34 kgms -1

Thus, high frequency waves such as x-rays and gamma rays have a short wavelengths and high energy while low frequency waves such as radio and IR have long wavelengths and low energy.

The electromagnetic spectrum


Spectra
Most objects in the universe either emit, reflect, or transmit some type of light. The spectrum of an object (the distrubution of light over the electromagnetic spectrum) is determined by an object's composition. Therefore, by observing an object's spectra we can determine it's composition. Depending on the nature of the radiation, different types of spectra can be observed. If the spectrum is composed by thermal emission radiated by the object itself an emission spectrum can be observed. If the spectrum is composed primarily of background light, some of which is transmitted by the object and some of which is absorbed, an absorbtion spectrum can be observed.

Each element has a characteristic fingerprint that is unique to that particular atomic makeup. For example, the element sodium shows two distinct yellow lines known as the Sodium D-lines at 588.9950 and 589.5924 nanometers. This color will be familiar to anyone who has seen a sodium vapor lamp. Below is both the absorption and and emission spectra of sodium.




Tomorrow we will learn how to make a spectroscope out of common household materials to observe various specta.

3 comments:

Anonymous said...

WOW!!!!!
this is amazin'!!!!
like LOL

Anonymous said...

this is really boring
im going to bed

Mekelle said...

You write very well.

My Zimbio