Science >> Physics for Kids

# Physics for Kids

## Behavior of Light as a Wave

In physics, light is a type of electromagnetic radiation that is visible to the eye. Light has the unique property that it can be described in physics as both a wave and as a stream of particles called photons.

On this page we will describe some of the behaviors of light as a wave including reflection, refraction, and diffraction.

Reflection

One of the most important wave-like behaviors of light is reflection. It is reflected light that we see with our eyes. How light reflects off objects affects the colors we see as well.

When a wave strikes a new medium, some of the wave will bounce off the surface. How reflective the surface is will determine how much light (and what wavelengths of light) will be reflected and how much will be absorbed or transmitted.

When light is reflected it obeys the law of reflection that is followed by waves. This means that the angle of the reflected wave of light will equal the angle of incidence of the incoming light wave. See the picture below for an example:

Types of Reflection

• Specular reflection - A specular reflection is when rays of light are reflected off a surface in a single outgoing direction. An example of this type of reflection is a mirror. Specular reflections occur on surfaces that are flat at the microscopic level such as polished silver or a smooth body of water.
• Diffuse reflection - A diffuse reflection is when a surface reflects rays of light in a broad range of directions. Diffuse reflections occur when a surface is rough at the microscopic level. The surface may appear or feel smooth, like a piece of paper, but it is actually rough at the microscopic level. This causes the beams of light to reflect at different angles.

Refraction

When light moves from one medium (like air) to another medium (like water) it will change directions. This is a "wave-like" behavior and is called refraction. In this way light behaves like other waves such as sound waves. The speed of the light wave also changes when it moves from medium to medium.

You can see an example of refraction of light in water if you put a straw in a glass of water. You will see how the straw seems to move to the side. This is the light wave bending as it enters the water.

Index of Refraction

In order to measure how light will behave in different substances, scientists use the index of refraction. This gives a ratio of the speed of light in a vacuum over the speed of light in the substance. The equation for the index of refraction is:

n = c/v

where n is the index of refraction, c is the speed of light in a vacuum, and v is the speed of light in the substance.

As an example, take the index of refraction for water which is 1.33. This means that the speed of light in a vacuum is 1.33 times faster than the speed of light in water.

 Diffraction Another wave-like property of light is diffraction. When light waves encounter an obstacle or pass through an opening they will bend. The diffraction of light can be seen in the silver lining around clouds as well as the patterns of light from the surface of a compact disc (see picture).

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