Light absorption

Title : Light absorption

Writer : Charles university 2nd faculty of medicine, Junghoo Lee

Table of contents

-Mechanism, example(phenomenon) of Light absorption -References

-MECHANISM, EXAMPLE(PHENOMENON) OF LIGHT ABSORPTION

Light is absorbed and converted into energy. In the case of plants, this process is known as photosynthesis. However, they are by no means the only species or objects that do this. Actually, all creatures or inorganic are capable of absorbing light. In all cases, absorption depends on the electromagnetic frequency of the light being transmitted (For example, the color) and the nature of the atoms of the object. Which means the absorption of light is related to the frequency very closely. If they are complimentary, light will be absorbed. If they are not complimentary, then the light will be transmitted or reflected.

In most cases, these processes occur at the same time. Since light is usually transmitted at various frequencies. (For example, the "natural light" which is made from Sun is also composed of lights of various frequencies; around 400~800nm EM radiation) So, most of objects will selectively absorb the light and also transmitting or reflecting some of the light. If absorption happened, heat energy will be generated.

Like as above, basically everything is capable of absorbing light. For the example, in case of organic molecule, they have quite special character for absorbing light. If the organic molecule has long "conjugation" then they absorb the light which has a long frequency. That happen because of pi-electron. Since Pi-electron can move through the chain(conjugation), as long as their conjugation length, they absorb lights of long frequency. Because light of long frequency has lower energy than light of short frequency.

For the another example of light absorption. Let's imagine that we are walking around the park with lots of grass and plenty of beautiful flowers. As you already know, all living things have their own color. We can infer from this, that all livings or inorganic things are reflecting and also absorbing the light simultaneously. As like the above, every matters have their own specific frequency so if the frequencies are complimentary then it will be absorbed and on the other hand, if the frequencies are not complimentary light will be reflected or transmitted. The colors we can see around is the result of transmission or reflection of light which is caused by non complimentary frequencies.

Absorption depends upon the state of an objects electrons. All electrons are known to vibrate at some-which is specific-frequencies, what is commonly known as their "natural" frequency. When light interacts with an atom with the same natural frequency, the electrons of that atom will become excited and set into a natural vibrational motion. During this vibration, the electrons of the atom interact with neighboring atoms in such a way as to convert this vibrational energy into thermal energy. Subsequently, the light energy is not to be seen again, hence why absorption is differentiated from reflection and transmission. And since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies of visible light.

By relying on this method, physicists are able to determine and identify the properties and material composition of an object by seeing which frequencies of light it is able to absorb. Whereas some materials are opaque to some wavelengths of light, they transparent to others. Wood, for example, is opaque to all forms of visible light. Glass and water, on the other hand, are opaque to ultraviolet light, but transparent to visible light.

Ultimately, absorption of electromagnetic radiation requires the generation of the opposite field, in other words, the field which has the opposite coefficient in the same mode. A good demonstration of this is color. If a material or matter absorbs light of certain wavelengths (or colors) of the spectrum, an observer will not see these colors in the reflected light. On the other hand if certain wavelengths of colors are reflected from the material, an observer will see them and see the material in those colors. For example, the leaves of green plants contain a pigment called chlorophyll, which absorbs the blue and red colors of the spectrum and reflects the green. Leaves therefore appear green, whereas reflected light often appears to the naked eye to be refracted into several colors of the spectrum. As a result, light absorption is related to matter's frequency(and frequency of light also) and wavelength of light.

-REFERENCES

- http://en.wikipedia.org/wiki/Absorption_%28electromagnetic_radiation%29 - http://navercast.naver.com/contents.nhn?contents_id=930 (Journal written by Dr. Joonwoo Park)