The Creation of LightThe Creation of Light

How is light created?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.

• 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.

Creating Light- (Vibrating Electrons)Creating Light- (Vibrating Electrons)

Here is an atom of phosphorusHere is an atom of phosphorus

Tiny non-seen nucleus Tiny non-seen nucleus

Circles are Circles are Energy Energy levels in the levels in the atomatom

electronelectron

Key to drawing:Key to drawing:

Creating Light- (Vibrating Electrons)Creating Light- (Vibrating Electrons)

Currently all electrons are moving but are Currently all electrons are moving but are not “vibrating”. not “vibrating”.

They are in their normal They are in their normal ground stateground state..

What causes a change?What causes a change?

Energy of some form will Energy of some form will hit the atomhit the atom

Energy approachingEnergy approaching

Creating Light- (Vibrating Electrons)Creating Light- (Vibrating Electrons)

Energy approachingEnergy approaching

1) If the energy is exactly the correct 1) If the energy is exactly the correct amount, one of the electrons will amount, one of the electrons will absorb it.absorb it.

Electrons absorbs energy Electrons absorbs energy of only a specific of only a specific (unique) frequency.(unique) frequency.

Creating Light- (Vibrating Electrons)Creating Light- (Vibrating Electrons)

2) With the new energy, the electron 2) With the new energy, the electron must jump to a farther energy level.must jump to a farther energy level.

This atom now has This atom now has energetic electrons energetic electrons in the in the excited stateexcited state. . (no longer normal (no longer normal ground state).ground state).

Now in a Now in a higher energy level. higher energy level.

Creating Light- (Vibrating Electrons)Creating Light- (Vibrating Electrons)

3) The absorption of energy makes 3) The absorption of energy makes the atom unstable. The electron the atom unstable. The electron must release its extra energy before must release its extra energy before it can return to ground state.it can return to ground state.

Creating Light- (Vibrating Electrons)Creating Light- (Vibrating Electrons)4) As the electron falls 4) As the electron falls back, the energy back, the energy released is at the exact released is at the exact frequency of the frequency of the energy it absorbed. energy it absorbed.

If it is just the right If it is just the right amount of energy, you amount of energy, you may see color!may see color!

The atom is now The atom is now in its ground in its ground state again.state again.

The Big PictureThe Big PictureEnergy absorbed by the electron causes it to Energy absorbed by the electron causes it to become excited and jump outward to a further become excited and jump outward to a further energy level.energy level.

As the electron falls back into its ground state, the As the electron falls back into its ground state, the same amount of energy is released in the form of same amount of energy is released in the form of light!light!

This process repeats thousandsThis process repeats thousandsof times a second.of times a second.

For any element, several electrons are vibrating at For any element, several electrons are vibrating at the same time, and they move between various the same time, and they move between various energy levels. energy levels.

Different wavelengths are given off depending on Different wavelengths are given off depending on how far the electron travels. The collection of how far the electron travels. The collection of wavelengths given off by an excited atom are wavelengths given off by an excited atom are called…… called……

SPECTRAL LINES!!!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.

• 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 LinesSpectral 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!

• 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 13

How can we use this? 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.

• 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.