Visible Light Rays Chapter 18 Visible Light Rays

Visible Light Rays Chapter 18

Visible Light Rays Essential Questions: • How can you manipulate light waves causing reflection, refraction, diffraction, and absorption? • How are light waves affected by mediums? Vocabulary: • Transparent • Translucent • Opaque • Reflection • Refraction • Diffraction • Absorption

This is an amusing example showing refraction of light by using a curved mirror.

S 8 P 4: Students will explore the wave nature of sound and electromagnetic radiation. a. Identify the characteristics of electromagnetic and mechanical waves. b. Describe how the behavior of light waves is manipulated causing reflection, refraction, diffraction, and absorption. d. Describe how the behavior of waves is affected by medium (such as air, water, solids).

• The reflection you see in a mirror depends on how the surface reflects light. • To show light reflects, you can represent light waves as straight lines called rays.

Regular Reflection • When parallel rays of light hit a smooth surface, reflection occurs. • All of the light rays are reflected at the same angle because of the smooth surface. So, you see a sharp reflection.

• The picture shows two kinds of reflection. In the choppy water, you do not see a clear reflection of the person in the boat. But in the smooth water, you see a sharp reflection.

Refraction of Light • In this example: • The light coming to your eye bends as it passes through three different mediums. • The mediums are water, the glass of the tank, and air. • As light passes from one medium to another, it refracts. • When light rays enter a medium at an angle, this causes the speed of light to slow down. • The change in speed causes the rays to refract, or change direction.

Refraction in Different Mediums • Some mediums cause light to bend more than others. This is called refraction. • Light travels fastest in gases, a little slower in liquids, and slowest in solids that it can penetrate, such as glass.

Diffraction of Light Diffraction of light is the bending of light waves around an object. The amount of light diffracted or which changes direction depends on an object's size. As light waves pass around the edge of an object or through an opening, light is diffracted or broken into the colors of the rainbow.

Absorption of Light Rays • Light rays are absorbed on translucent and opaque objects. • Every opaque object absorbs some wavelengths of light and reflects others. • The color of an opaque object depends on the material the object is made of and the color of the light striking the object. • All other colors are absorbed by the medium.

• For example, look at the apple shown in the picture. The apple appears red because it reflects red wavelengths of light. The apple absorbs other colors of light. • Black light absorbs all • The leaf looks green because it reflects green colors. White light reflects light and absorbs the otherall colors. A color, such as green, happens because colors. green light is reflected and all other light is absorbed.

Transparent Materials • A transparent material transmits most of the light that strikes it. • The light passes right through without being scattered. This allows you to see clearly what is on the other side. • Examples: Clear glass, water, and air.

Translucent Materials • A translucent material scatters light as it passes through. • You can usually see something behind a translucent object, but the details are blurred. • Examples: Wax paper and a frosted glass like the middle glass.

Opaque Materials • An opaque material reflects or absorbs all of the light that strikes it. • You cannot see through opaque materials because light cannot pass through them. • Examples: Wood, metal, and tightly woven fabric.

Mini Check 1. An object is considered ________ is light passes straight through it. 2. An object is considered _____ if the light is scattered as it moves through. 3. An object is considered ______if light is completely reflected or absorbed by the object. 4. _______ happens when light bounces off a smooth surface at an angle. 5. _______ happens when light enters a medium at an angle, causing light to slow down. 6. Light travels slowest in a _______ medium, faster in a _____ medium, and fastest in a _________ medium. 7. If light is ________, it is completely “soaked up” by the matter. 8. We see black light because black ______ all colors. We see white light because it _____ all colors. We see a color, like blue, because it _____ the blue and ____ all the other colors.

Answers to Mini Check 1. 2. 3. 4. 5. 6. 7. 8. Transparent Translucent Opaque Reflection Refraction Solid, liquid, gas Absorbed Absorbs, reflects, absorbs

Textured glass Vellum Stained glass velvet Oiled paper