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Lights and Matter: A Guide to Optics

Optics is the scientific study of light. Its study is interested in finding out the nature and properties of light that can make it widely applied in different sectors. Optics defines light has having both particle and wave nature. It also tries to give explanations to the optical wonders (such as rainbows) that occur almost everyday.

What is light?

Light is a kind of radian energy with wavelengths between 3,900 and 7,700 Angstroms and a speed of approximately 300,000,000 m/s. Light behaves as waves and particles. Just like other forms of electromagnetic energy, light can travel through long distance. This distance covered by light when it travels is called wavelength. It is possible to measure the wavelength of light because it travels like waves. It is the distance between successive points (highest or lowest point) that is called the wavelength. Other wave properties that are possessed by light include frequency, period and speed. As particles, light behaves as if there are distinct particles in it that contain photons. Photons have fixed energy levels that affect the color of light. Since the energy level of photons is fixed, altering the energy is only possible when the wavelength is changed. Light has properties such as reflection and refraction. These properties are applied in the knowledge of colors, lenses, lasers, fiber optics and rainbows.

  • Lights as wave- Light can be regarded as wave. To prove this, its wavelength, which is the distance between two successive high or low ends, can be measured.
  • Wave particle duality- This postulates that light possesses both properties of matter and wave.
  • The double slit experiment- This experiment was conducted to test that light possesses properties of waves and particles.


Reflection occurs when light changes its direction as a result of collision on another object. Reflection is governed by the law that states that the angle of the incident ray must be equal to the angle of reflection. Reflection is applied in sonar because of its ability to form echoes and in geology; reflection is used to form seismic waves. 

  • Tutorial on the reflection of light- Reflection occurs when the object that receives the light rays cannot absorb the incident ray.
  • Reflection of light with examples-  site contains pictures to explain the phenomenon about reflection.
  • Reflection of light from a surface- Objects have different colors because of the color spectrum of the incident ray.
  • The law of reflection- The angle of incidence must be equal to the angle of reflection when the light is incident upon a plane surface. Furthermore, the incident, reflection and normal rays all lie on the same plane.


Refraction occurs when light passes through objects of different densities. As a matter of fact, the densities of objects affect the speed of light passing through them. There are two major laws that support refraction. The first law states that the rays traveling to the object, the ray going back after colliding with the object and the ray coming straight to the object at an angle of 90 degrees must all lie on the same plane. Secondly, the sine of the angle of incidence divided by the sine of the angle of refraction gives a constant known as the refractive index. Refraction can cause illusions. For instance, when wood is dropped into a glass of water, its depth when viewed from the top is actually different from the real depth. Similarly, space crafts can appear at different levels of the sky when viewed at different locations. The occurrence of mirage (resemblance of a pool of water) on the road observed on a sunny day is caused by refraction.

  • Definition of refraction- Refraction of light occurs when light bends as a result of passing through surfaces that have different densities.
  • Refraction- Refraction is an important phenomenon in optics. It is applied in building lenses for eye-glasses and telescope.
  • Information of refraction- This site is very rich in content about most things to know about refraction.


The different kinds of colors on record today are actually as a result of the combination of some different kinds of colors. Colors are perceived from the way visual organs react with the light in the environment. For instance, when an object reflects the primary colors: red, green and blue, the object is seen as white. On the other hand, if it does not reflect any of the colors, the object will appear as black. Thus, the way color is seen depends on the addition and subtraction of the three primary colors. The color reflected by an object determines the judgment given as the color of that object. Dyes, pigments and filters are used in making clothes to affect colors because of their abilities to absorb or subtract colors. For example, yellow shirts are seen as yellow when dyes that can absorb the blue spectrum of light rays (containing red, green and blue spectrums) are used so that the reflected green and red combine to form yellow.

  • Colors- Substances can have different colors when viewed through different colors.
  • Why and what is color?- This site contains some questions and answers about colors.


Lenses and mirrors are important in everyday life. However, only few know their working principles. Lenses and mirrors act the way they do as a result of how light determines their focal length. A focal length is the distance between the focal point and the lens. The focal point is the point where light rays meet after moving through the lens. There are two kinds of lenses: concave and the convex. The convex lens has positive focal length because their sides bulge outward to make light converge to a focal length. The concave lens on the other hand has a negative focal length because their sides bulge inward to make light diverge to the focal length. Convex lens are therefore used to produce virtual images and the applications are evident in the production of cameras and side mirrors of vehicles while concave lens, which produces real images are widely used in making spherical and cylindrical lenses.

  • Lens optics- Lenses are able to enlarge the original size of images when light passes through it.
  • How lenses work- Lenses work according to their different kinds. For instance, there re convex and concave lenses.
  • Lens education- This site is suitable to learn how lens operate. It is particularly helpful to children because of its details.

Optic wonders

The properties of light make it possible to observe certain phenomena that are very interesting and puzzling to study. Some of these are rainbows, fiber optics, lasers, binoculars, periscopes and kaleidoscopes.

Rainbow: Rainbows appear after rain because of the tiny droplets of rain that reflect the white light that pass through them. For rainbows to form there has to be millions of tiny rain droplets so that there will be several reflections to give the full color of the rainbow. Rainbows formed after a short rain will not have the complete colors since the white light in each droplet of rain will not be completely reflected.

  • How rainbows are made- Rainbows occur as a result of the reflection of light caused by the tiny droplets of rain. 

Fiber optics: Fiber optics are used in the telecommunication industry to carry digital signals with light. They are made of glass and they are neither stiff nor easy to break; rather, they can be bent. Fiber optics has the following advantages: cost effectiveness, need for little parking space, ability to carry more information and the ability to retain information when traveling through a very long distance.

  • How optical fibers work- Optical fibers use the advantage of the high speed of light to send signals into a home computer.
  • Definition of optical fiber- Optical fibers are substances made of glass and are used to transfer images.

Lasers:Unlike light from the sun, which contains other colors, lasers produce just one kind of light with its specific wavelength. The light they produce is essential for surgical operations.

  • Understanding lasers- Lasers have a wide range of applications such as correcting poor vision.
  • How lasers work- Lasers direct light in only one direction. The site gives details on what should be known about its working principles including the history.
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