LIGHT

Light plays a very important role in our lives. Without light we would not be able to see. Light from the sun generates heat, and can be used to generate electricity. To do this, light must travel to us.

Seeing the Light

Let’s take a moment to talk about visible light. As you can tell by the name, visible light is the light that humans can see. More specifically, you see the light that is not absorbed by objects. Green plants are green because they absorb all of the colors of the visible spectrum except the green color (you could also say the green wavelengths). A red wall is red to your eyes because it is not absorbing light from the red wavelengths. Mirrors reflect all of the colors of visible light.

We describe the world the way we see it as humans. Other living things on Earth see the world in different ways. Dogs only see things in black, white and gray. Some insects see colors that none of us can see. When you are learning about visible light you should remember we mean visible to humans. We should also mention that not all humans can see all the colors. There is an eye defect called color-blindness that affects many men. Color-blind men cannot see certain colors of the spectrum. It has to do with a genetic defect in their eyes.

Edges of Visibility

Although we can’t see them with our eyes, some wavelengths of light that bookend the visible spectrum are also important. Infrared radiation is next to the red portion of the spectrum. Infrared light is heat. Scientists use infrared light sensing optics when they want to see differences in temperature. Ultraviolet radiation (UV) is just beyond the violet end of the visible spectrum. UV light is given off by the Sun and absorbed by ozone in the atmosphere. Ultraviolet light can also mutate cells in your skin and give you skin cancer.

Reflection Basics

When a light ray hits an object and bounces off, it is called reflection. When you think of reflection, think about mirrors. They reflect all of the light. That is the reason you can see yourself. Even the ocean reflects light, just not all of it. If you are above the ocean, you can’t see the reflection that well, but when you are at an angle, look closely; you can see a reflection of the sky. So the ocean only has partial reflectivity.

Refraction Basics

When light moves from one substance to another it changes speed and direction. That change in direction is called refraction.

Bending Light with Refraction

Lenses are pieces of glass that bend light. The easiest thing to think about is lenses in eyeglasses. People who do not have 20/20 vision might see things a little out of focus. They wear glasses or contact lenses to make their sight clearer. Those glasses have specially ground lenses that bend the rays of light just enough to focus the image for the person to see properly. All lenses bend and refract rays of light.

In the refraction section we said that light changes speeds when it moves from one medium to another. A medium is a substance like water, air, or glass. When light slows down or speeds up it changes direction a little bit. There are three basic shapes that a lens can have: concave, convex, and planar. A concave shape is bowed inward, like looking into a mixing bowl. Convex is just the opposite, bowed outward. Have you ever seen those mirrors in the grocery stores, where everything is reflected in a spherical way? That’s convex. Planar is just that, a plane. It’s a flat surface. Just think of a planar mirror on your wall.

Using Lenses

Telescopes and microscopes are excellent examples of how lenses are used every day. By using different combinations of lenses, light is focused to create an image we could not see with the naked eye. Telescopes are able to see very distant objects that are very small to our sight and magnify them so we can see the details. The larger telescopes offer a greater ability to see objects that are more distant. Microscopes work with a similar idea but are concerned with size, not distance. Microscopes enlarge very small objects that are close to the viewer.

Using Prisms

Prisms are a very special type of lens. When refraction is at work in a prism it breaks the beam of visible light into its basic colors. In visible light, the magic colors you can see are red, orange, yellow, green, blue, indigo, and violet. Scientists say ROY-G-BIV. A prism is made up of two planar surfaces at an angle. It uses the slower speed of light in glass to its advantage by refracting the light twice. Because of the different wavelengths of light, each color is refracted a different amount. When the light ray leaves the prism, it speeds up again (entering the air) and refracts a second time. That second dispersal creates the colorful spectrum of colors.

The world around you is full of wonderful colors. The beautiful flowers, the green meadows and the blue sky show different colors. We see colors only when light is shining. When it is dark we cannot see colors.

Sunlight is made up of a number of colors but what you see is really white color. When all the Sun’s colors are mixed together, the resulting color is white. Different colors of the light travel at different speeds in glass and in water. When the white light of the sun passes from air to water or air to glass, the different colors of the sunlight bend at different angles thus separating into the individual colors we see.

Scientists generally use a glass triangle called a prism to experiment with light, when the white light hits the glass prism, each color of the light bends at a different angle and the different colors separate into a rainbow.

During a summer rain, we often see a rainbow when the sun is out. Each drop of water falling down acts as a prism. As the sunlight passes through these raindrops, the light rays bend and separate into the 7 colors of the rainbow. The colors always separate in the same order as violet, indigo, blue, green, yellow, orange, and red. To see any colors, the retinal cone cells must be stimulated by light.
The color of anything depends on the type of light sent to our eyes; light is necessary if we are to have any perception of color at all. An object is “colored,” because of the light it reflects—all other colors are absorbed into that specific object. For example, a leaf appears green because it reflects the green light and absorbs the rest of the colors.

You can see color when receptor cells (called cones) on your eye’s retina are stimulated by light. There are three types of cones, each sensitive to a particular color range. If one or more of the three types of cones becomes fatigued to the point where it responds less strongly than it normally would, the color you perceive from a given object will change.

Enjoy these activities and video about light!

http://www.bbc.co.uk/schools/scienceclips/ages/7_8/light_shadows_fs.shtml Exercise about shadows

http://www.primaryresources.co.uk/science/powerpoint/transparent.swf Transparent, translucent and opaque objects

http://www.youtube.com/watch?v=2P3nKJHO2j0 Video about light, reflection and refraction

  1. Aún no hay comentarios.
  1. No trackbacks yet.

Responder

Por favor, inicia sesión con uno de estos métodos para publicar tu comentario:

Logo de WordPress.com

Estás comentando usando tu cuenta de WordPress.com. Cerrar sesión / Cambiar )

Imagen de Twitter

Estás comentando usando tu cuenta de Twitter. Cerrar sesión / Cambiar )

Foto de Facebook

Estás comentando usando tu cuenta de Facebook. Cerrar sesión / Cambiar )

Google+ photo

Estás comentando usando tu cuenta de Google+. Cerrar sesión / Cambiar )

Conectando a %s