Unit 1 Question 2

Question

Explain in your words the differences between three types of spectra (continuous, emission, absorption), and provide examples on where and when would one observe each of those spectra in the surrounding world.

 

Answer 1

To define the differences between three types of spectra, let's first define a "spectra" as an electro-magnetic wave. We can further define an electro-magnetic wave as merely oscillating magnetic and electric fields such that the oscillating electric field induces an oscillating magnetic field in response. Light is the most familiar example of an electro-magnetic wave. Because light is really then just oscillating magnetic and electric fields, it is capable of traveling (propagating) through empty space; such as from the Sun to our earth. If we think of the electro-magnetic oscillations being limited to one 2-dimensional plane, we can more easily comprehend the characteristic frequency and wavelength of a particular electro-magnetic (E-M) wave.

In a continuous spectrum E-M wave, the wavelength and frequency range is not limited. Very short wavelength E-M waves result in very high frequencies and very high penetration energies, such as gamma rays and X-rays, while very long wavelength E-M waves result in very low frequencies and low penetration energies such as FM and AM radio waves.

An absorption spectrum results when we consider the part of the continuous E-M spectrum which is absorbed, or subtracted out, when the waves interact with atoms of some material. In the process, momentum and energy is given to some atoms in the material. An example would be white light sent through a red piece of glass or film. Red glass or film both reflects and transmits light in the red spectrum (red wavelengths) while all other colors (Blue - Green etc.) are absorbed. The red light is part of the emission spectrum, while the non-transmitted (absorbed) colors comprise or make up the absorption spectrum.

Watch the top of a soap bubble! Right before it pops the color of the top of the soap bubble should appear to be...black. Why? Because just as the bubble is about to pop, it is too thin to reflect any light back to your eyes, so you see black (the absence of light).