Electromagnetic Waves Physical Science 2014

Properties of Light Light travels extremely fast and over long distances. Light carries energy and information. Light travels in straight lines. Light bounces and bends when it comes in contact with objects. Light has color. Light has different intensities, can be bright or dim.

How is light produced? Most light is produced by atoms. When you put some energy into the atom, it excites the atom’s electrons. Light is produced when the electron releases this energy.

Electromagnetic Waves There are other forms of radiant (light) energy that share the same properties of light, they are called electromagnetic waves. Electromagnetic waves are transverse waves. These waves vary in frequency, wavelength, and energy. All of these waves are summarized in the electromagnetic spectrum.

Electric Light The process of making light with heat is called incandescence. Incandescent bulbs generate light when electricity passes through a thin piece of metal wire called a filament. The filament heats up and gives off light. Electric energy changes to light and heat energy

16.1 Electric Light The other common kind of electric light is the fluorescent bulb. Fluorescent bulbs convert electricity directly to light without generating a lot of heat. (saves energy) Fluorescent bulbs use high-voltage electricity to energize atoms of gas that fill the bulb.

16.1 Light carries energy and power Light is a form of energy that travels. The intensity of light is the amount of energy per second falling on a surface. Most light sources distribute their light equally in all directions, making a spherical pattern. Because light spreads out in a sphere, the intensity decreases the farther you get from the source.

16.1 Light intensity The intensity of light from a small source follows an inverse square law because its intensity diminishes as the square of the distance.

Visible Light and Energy

Speed of Light The speed at which light travels through air is about 300 million meters per second (3.0x108 m/s). The speed of light is so important in physics that it is given its own symbol, a lower case “c”. The speed of light is the speed at which ALL electromagnetic waves travel through air.

How we See Color: RGB – Additive Color Process Our eyes work according to an additive color process — 3 photoreceptors (red, green, and blue) in the eye operate together so that we see millions of different colors. The additive primary colors are red, green, and blue.

Making an RGB color image A television makes different colors by lighting red, green, and blue pixels in different proportions. Color images in TVs and computers are based on the RGB color model.

CMYK – Subtractive Color Process The subtractive color process is often called CMYK for the four pigments it uses. Pigments are chemicals in the dyes and paints that absorb some colors and reflect other colors. CMYK stands for cyan, magenta, yellow, and black.

Subtractive color process When we see an object, the light that reaches our eyes can come from two different processes: The light can be emitted directly from the object, like a light bulb or glow stick. The light can come from somewhere else, like the sun, and we see the objects by reflected light.

Four Ways light can be affected by matter. The light can bounce off (reflection). The light can go through but be bent. (refraction). The light can transfer its energy to the material (absorption). The light can go through a small opening and bend on the other side. (diffraction).

Why is the sky blue? The red color in the sky at sunrise & sunset is due to an effect called Rayleigh scattering. The sky appears to be blue in the day-time (when the sun is closest to us) because the Oxygen and Nitrogen in the atmosphere scatter violet and blue light due to their small size. This blue light is received by the observer.

Why does the image of the sun appear reddish at sunrise & sunset? The light has to travels through more atmosphere during sunrise and sunset because the distance that the light has to travel from the Sun to an observer is at its greatest. Blue/violet light is scattered the most & red light is scattered the least. This means the large amount of blue and violet light has been scattered so the light that is received by an observer is mostly of a longer wavelength and therefore appears to be red.

Reflection Reflection is the process of light rays bouncing off a surface. There are two types: When light rays strike a rough surface, they are randomly reflected. When you look at a diffuse reflecting surface you see the surface itself. Rays of light that strikes a shiny surface (like a mirror) create single reflected rays.

The Law of Reflection States: The angle of incidence is always equal to the angle of reflection.

Refraction Refraction occurs when light bends while crossing a surface or moving through material.

Lenses - cause refraction

Index of Refraction An important property of transparent substances is the index of refraction. The index of refraction is the ratio of the speed of light in a vacuum to the speed of light in that substance.

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