The Creation of Light

How is light created? All light starts as a vibration of charged particles, electrons that move between different energy levels. These vibrations are caused by atoms absorbing various types of energy. These are the main notes taken by students on light production- the next pages are gone over quickly-students are encouraged to print them out if they really want them.

Creating Light- (Vibrating Electrons) Here is an atom of phosphorus Tiny non-seen nucleus Key to drawing: electron Circles are Energy levels in the atom

Creating Light- (Vibrating Electrons) Currently all electrons are moving but are not “vibrating”. They are in their normal ground state. What causes a change? Energy of some form will hit the atom Energy approaching

Creating Light- (Vibrating Electrons) 1) If the energy is exactly the correct amount, one of the electrons will absorb it. Electrons absorbs energy of only a specific (unique) frequency. Energy approaching

Creating Light- (Vibrating Electrons) 2) With the new energy, the electron must jump to a farther energy level. This atom now has energetic electrons in the excited state. (no longer normal ground state). Now in a higher energy level.

Creating Light- (Vibrating Electrons) 3) The absorption of energy makes the atom unstable. The electron must release its extra energy before it can return to ground state.

Creating Light- (Vibrating Electrons) 4) As the electron falls back, the energy released is at the exact frequency of the energy it absorbed. If it is just the right amount of energy, you may see color! The atom is now in its ground state again.

The Big Picture Energy absorbed by the electron causes it to become excited and jump outward to a further energy level. As the electron falls back into its ground state, the same amount of energy is released in the form of light! This process repeats thousands of times a second.

For any element, several electrons are vibrating at the same time, and they move between various energy levels. Different wavelengths are given off depending on how far the electron travels. The collection of wavelengths given off by an excited atom are called……

SPECTRAL LINES!!! You can see an element’s spectral lines by passing the light through a small opening. The light then passes through a prism which separates the light into it’s individual wavelengths.

Spectral Lines Every element has a DIFFERENT set of spectral lines and can be used to identify the element. It’s like each element has it’s own team colors!

Spring 2006 UCSD: Physics 8; 2006

Emission vs Absorption

How can we use this? Gases, stars, and planets are made of MANY different elements. If we look at the light given off or reflected from these planets we can examine their composition due to their spectral lines.