Light Energy What is light?

How does light travel?How is light reflected, refracted, and absorbed?

How does light determine how we see the color of an object?

What is light?

Light is a form of energy that can be released by an atom. It is made up of many small particles called light photons.

Atoms release light photons when their electrons become excited. Electrons are particles that move around an atom's center or nucleus. Electrons move in different paths around the nucleus. When something happens to an atom to add energy to it, like it gets heated, the electrons may jump to different paths. Soon they fall back to their original path. When they return to their original path, they may release energy in the form of photons of light .

How does light travel?

Light photons travel in waves made up of electrical and magnetic energy. But, light waves can travel through space where there is no material. Light photons travel very rapidly: 186,000 miles per second.

How does light travel?

Electromagnetic waves include more than visible light. They also include cosmic rays, gamma rays, radio waves, and other forms of electromagnetic radiation. We only see some of this energy as visible light.

How do we see light?

Any light that you see is made up of a collection of one or more photons traveling through space as electromagnetic waves. In total darkness, our eyes are actually able to sense single photons, but generally the light we see in our daily lives comes to us in the form of zillions of photons produced by light sources like the Sun or a flashlight.

If you look around you right now, there is probably a light source in the room producing photons, and objects in the room that reflect those photons. Your eyes absorb some of the photons flowing through the room, and that is how you see.

How is light reflected?

Reflection is when incoming light hits an object and bounces off. Very smooth surfaces such as mirrors reflect almost all incoming light.

We now know this can’t happen!What you see in the mirror is reflected light.

How is light refracted?

Refraction is when light waves change direction as they pass from one material to another. Light travels at different speeds as it passes through different materials. Light travels slower in air than in a vacuum, and even slower in water. The change in speed bends the light.

Different wavelengths of light are slowed at different rates, which causes them to bend at different angles. For example, when the full spectrum of visible light travels through the glass of a prism or water droplets in air, the wavelengths are separated into the colors of the rainbow.

How is light absorbed?

Sometimes when light hits an object, the atoms and molecules in that object start to vibrate as they absorb the light.

When a dark surface like a black asphalt road absorbs light, it can get hot enough to cook an egg! Light energy has turned into heat energy that cooks the egg.

Darker colored materials absorb more light than lighter colored materials. The same egg might not cook on a light grey cement sidewalk!

How is light reflected, refracted, and absorbed?

Why is the sky blue?

The sky appears blue because of the scattering of light. Light at shorter wavelengths—blue and violet—is scattered by nitrogen and oxygen as it passes through the atmosphere. Longer wavelengths of light—red and yellow—transmit through the atmosphere.

This scattering of light at shorter wavelengths illuminates the skies with light from the blue and violet end of the visible spectrum. Even though violet is scattered more than blue, the sky looks blue to us because our eyes are more sensitive to blue light.

The same thing happens in the ocean’s water, so it also appears blue.

How does light determine how we see the color of an object?

Color refers to the different wavelengths of light in the visible light spectrum that our eyes can see.

When we look with our eyes at an object, we are really seeing the wavelengths of light that are reflected by the object. The object absorbs the other wavelengths.

The physical and chemical composition of matter in the object determines which wavelength (or color) is reflected.

How does light determine how we see the color of an object?

We see objects of a certain color because they reflect part of the light spectrum and absorb the rest. So, the apple leaf appear green because it absorbs all the colors except green. The apple skin appears red because it absorbs all the colors except red. The color we see is the color reflected by the object.

How does light determine how we see the color of an object?

Color originates in light. Sunlight, as we perceive it, is colorless. In reality, a rainbow is testimony to the fact that all the colors of the spectrum are present in white light.

When white light is bent or reflected, as through a prism, it can separate into the different colors of the spectrum.

A rainbow is white light that is reflected and bent by water droplets in the air, causing the colors of the light to separate into a range of red, orange, yellow, green, blue, and indigo/violet.

How does light determine how we see the color of an object?

A transparent material, such as glass, allows light to pass through it very well.

A translucent material absorbs some of the light.

An opaque material allows no light to pass through.

How does light cause heat?

When the electromagnetic radiation from the sun encounters a material, it causes the atoms in the material to vibrate, generating heat and causing the object to release thermal energy. Vibrating atoms hit other atoms and heat is moved through a material.

In heated liquids and gases, convection causes the hotter material to move upward and the colder material to sink.

In heated solids, conduction between the closely vibrating atoms moves heat through the material evenly. So, don’t use a metal spoon to stir hot soup!

How is heat measured?

Heat is measured in degrees, using the Celsius, Fahrenheit, or another type of scale.

The movement of heat through a material depends on the source of heat and the type of material. Some materials, like metals, move heat well by conduction. Wood does not conduct heat well.

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