Grade 8 SCIENCE LIGHT

12/31/15

Module 6: Colors of Light

The Science of Light has gone all the way from a mere transfer of energy to the creation of colors for entertainment and other purposes. Most of our gadgets are light emitting for efficiency when used at night. In the field of medicine light is used to cut through the skin for surgery as in laparoscopy. The health sciences are also using light for other medical purposes. But the most important purpose is for humans and other animals to see the beautiful world through light.

In this module, you will learn some properties and characteristics of light. Among the characteristics and properties of light, we will focus on refraction and specifically, dispersion of light. We will try to find through simple activities how light disperse to form the colors of light. We will also try to find the hierarchy of colors of light in terms of frequency, wavelength, and energy.

Refraction of Light

Light exhibits the characteristics and properties of a wave. It is classified as an electromagnetic wave located between the spectrum of infrared and ultraviolet. As an electromagnetic wave it does not need a medium in order to propagate. It moves in its maximum speed in vacuum. But this speed decreases as it moves along different media. This characteristic of light consequently shows bending when it crosses the boundary between two media. Apparent distortion of an object seen at the boundary between media is observed.

Refraction is the bending of light when it travels from one medium to another of different optical densities. Light travels approximately at a speed of 3 x 108 m/s in a vacuum. This speed decreases when light travels in a dense medium. This means that the speed of light is dependent on the properties of the medium. In the case of light, it is dependent on the optical density of the medium. The optical density of the medium is different from its physical density. 

Physical density is described as the mass per unit volume of the medium. On the other hand, the sluggishness of the atoms of a medium to maintain the absorbed energy before reemitting it is called optical density. When light crosses the boundary of two media of different optical density, a change in speed takes place. This change in speed is manifested as bending of the light ray.

A known indicator of the optical density of a material is the index of refraction of the material. Index of refraction represented by the symbol n is the ratio of the speed of light in vacuum and its speed in another medium.

The index of refraction of a material is a quantity that compares the speed of light in that material to its speed in a vacuum. Since the speed of light in vacuum is the highest attainable speed in the universe, the index of refraction is always greater than 1.

01/12/15

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Activity 1: Colors of the rainbow, colors of light.

1.  Pass white light through a prism and you will get the colors

a.  Red

b.  Orange

c.  Yellow

d.  Green

e.  Blue

f.  Indigo

g.  Violet

2.  The refractive index varies on the wavelength of the wavelength of colors.

3.  Some colors are not that visible when the prism is in the water.

4.  Depends on the frequency speed:

a.  Slower frequency: Red

b.  Faster frequency: Blue

Activity 2: Red versus violet...

1.  The colors were arranged, depending on their frequency.

2.  Wavelength is decreased provided the speed of shaking or disturbing the medium is the same or constant.

Material/Color of light (nm) n Acrylic  Red  Orange  Yellow  Green  Blue  Violet 650 600 550 500 450 400 1.488 1.490 1.497 1.495 1.502 1.508 Material/Color of light (nm) n Crown Glass  Red  Orange  Yellow  Green  Blue  Violet 650 600 550 500 440 400 1.512 1.515 1.518 1.520 1.525 1.530

01/19/16

Activity 3: Which color has the most energy?

1.  The color with the lowest temperature:

a.  Red

2.  The color with the highest temperature:

a.  Violet

3.  The color with the most energy passing through

a.  Red

4.  The color with the least energy passing through

a.  Violet

Activity 4: Color Spectrum

1.  Color with the shortest wavelength

a.  Violet

2.  Color with slowest frequency

a.  Red

3.  Wavelength increases, frequency decreases.

4.  Frequency decreases, Wavelength increases.

Summary

The dual nature of light brings about several observable phenomena in the sky. Light as a wave exhibits properties just like any other waves. When light moves from one medium to another of a different density, the speed changes, bringing about changes in the direction of the refracted ray with respect to the normal line.

This is known as refraction. Refraction of light, however, may result in a display of colors of light when it passes through materials that can have varied refractive indices for every wavelength of color that passes through them. 

A glass prism, for example, has varied refractive indices per wavelength of color resulting in different bending angles of the refracted colors of light with respect to the normal line. This phenomenon is better known as dispersion.

With the concept of dispersion, colors of light are hierarchically arranged as R.O.Y.G.B.I.V according to frequency and energy of the colors of light. Red happens to have the lowest frequency and the least energy. Energy and frequency increases as one moves from red light towards violet light. 

This display of colors of lights by dispersion of white light is one of the consequences of refraction of light aside from the apparent depth mentioned above. Other consequences are spectacular phenomenon of blue skies and red sunsets.