# The color and energy of Light

Light is an electromagnetic waves. We are able to see because of light. Our eyes will catch the light that enters through the retina and process it in our brain. The light that was caught by the retina of the eye have some colors. The light that is able to be analyzed by the brain is hereinafter referred to as with visible light. There are many other types of light that doesn't look or visible to our eyes. an example of this light is ultraviolet light, radio waves, microwaves or x-rays. the different types of light is based on the wavelength or frequency of the light. Wave length is the length of a wave to complete one lap hills and valleys as shown in Figure 1.

While the frequency is the time it takes to reach one of the wavelengths. As we know, all electromagnetic waves running at the same speed that is approaching 300000 km/s, then the relationship between velocity, wavelength and frequency are

$c&space;left&space;(&space;frac{m}{s}&space;right&space;)=lambdaleft&space;(&space;m&space;right&space;)&space;times&space;fleft&space;(&space;frac{1}{s}&space;right&space;)$

Figure 2 shows the kinds of electromagnetic waves based on the order of the wavelength of the most the most long to short.

It can be seen that the visible light is merely a small part of the electromagnetic waves. The shortest wavelength is the wavelength of x-rays and radio waves are the longest.

Electromagnetic waves has been widely applied in everyday life ranging from photos of x-rays to find out the bone structure, move data using wi-fi, radio, tv communications tools to microwave that is in our kitchen.

Electromagnetic waves have energy is different depending on the seriousness of the great frequency of a wave. The greater the frequency will be even greater energy. And vice versa. The relationship between frequency and energy is expressed by the following equation

$E=f&space;times&space;h$

With h is planck's constant of j/s$6.62606957times&space;10^{{-34}}$ and f is the frequency (1/s).
A molecule can absorb a certain light waves used for energy electron excitation of molecular vibration, movement and the rotary motion of the molecule. Chlorophyll molecules have two kinds of excitation of electrons as shown on the previous discussion. In Figure 3 it can be seen that the first excitation of chlorophyll is a light red and the second is the excitation light blue. The first excitation energy needs are smaller because the electrons move with smaller differences compared to the excitation of the second. The greater the distance the higher electron excitation energy is absorbed.

##### Reference:

[1] slide presentation college online www.edx.org with the university of Tokyo with the topic "quantum mechanic of moleculs" weekend 1

[2] video lectures online www.edx.org with the university of Tokyo with the topic "quantum mechanic of moleculs" weekend 1

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