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Bellringer

What do you think light is? Is light made of matter? Can light travel through space?

Explain your answers in your lab journal.


Light: An Electromagnetic Wave

• Light is a type of energy that travels as a wave. But unlike most other types of waves, light does not require matter through which to travel.

• An electromagnetic wave is a wave that consists of electric and magnetic fields that vibrate at right angles to each other.


Visible Light

• Visible Light from the Sun Visible light is the very narrow range of wavelengths and frequencies in the EM

spectrum that humans eyes respond to. Visible light waves have wavelengths between 400 nm and 700 nm.

•White light is visible light of all wavelengths combined.


Visible Light, continued

• Colors of Light Humans see different wavelengths of visible light as different colors. The longest wave-lengths are seen as red light. The shortest wave-lengths are seen as violet light.

• The range of colors is called the visible spectrum.


Reflection

• Reflection happens when light waves bounce off an object. Light reflects off objects all around you.

• The Law of Reflection states that the angle of incidence is equal to the angle of reflection.


•You see your image in a mirror because of regular reflection.

• Regular reflection happens when light reflects off a very smooth surface. All the light beams bouncing off a smooth surface are reflected at the same angle.

Types of Reflection


Reflection, continued

• You cannot see your image in a wall because of diffuse reflection.

• Diffuse reflection happens when light reflects off a rough surface, such as a wall. Light beams that hit a rough surface reflect at many different angles.


Reflection, continued

• Light Source or Reflection? The tail of a firefly, flames, light bulbs, and the sun are light sources. You can see a light source in the dark because its light passes directly into your eyes.

• Most things around you are not light sources. But you can see them because light from light sources reflects off the objects and the travels to your eyes.


Absorption and Scattering

• Absorption of Light The transfer of energy carried by light waves is called absorption.

• When a beam of light shines through the air, particles in the air absorb some of the light’s energy. As a result, the beam of light becomes dim.


Absorption and Scattering, continued

• Scattering An interaction of light with matter that causes light to change direction is scattering. Light scatters in all directions after colliding with particles of matter.

• Light can be scattered out of a beam by air particles. This scattered light allows you to see things outside of the beam. But, the beam becomes dimmer because light is scattered out of it.


Refraction

• Refraction is the bending of a wave as it passes at an angle from one material to another.

• Refraction of light waves occurs because the speed of light varies depending on the material through which the waves are traveling.•When a wave enters a new material at an angle, the part of the wave that enters first begins traveling at a different speed from that of the rest of the wave.


Refraction, continued

• A lens is a transparent object that refracts light to form an image.• Convex lenses are thicker in the middle than at the edges.

•When light beams pass through a convex lens, the beams are refracted toward each other.

• Concave lenses are thinner in the middle than at the edges.

•When light beams pass through a concave lens, the beams are refracted away from each other.



• Refraction and Optical Illusions Your brain always interprets light as traveling in straight lines.

• But when you look an an object that is underwater, the light reflecting off the object does not travel in a straight line. Instead, it refracts.



• Because of refraction, the cat and the fish see optical illusions.



• Refraction and Color Separation White light is composed of all the wavelengths of visible light. The different wavelengths of visible light are seen by humans as different colors.

• When white light is refracted, the amount that the light bends depends on its wavelength.



• Waves with short wavelengths bend more than waves with long wavelengths.

• White light can be separated into different colors during refraction, as shown below.


Diffraction

• Diffraction is the bending of waves around barriers or through openings.

• The amount a wave diffracts depends on its wavelength and the size of the barrier or opening.

• The greatest amount of diffraction occurs when the barrier or opening is the same size or smaller than the wavelength.

Chapter O3


Diffraction, continued

• Diffraction and Wavelength The wavelength of visible light is very small.

• So, a visible light wave cannot diffract very much unless it passes through a narrow opening, around sharp edges, or around a small barrier.


Interference

• Interference is a wave interaction that happens when two or more waves overlap.

• Constructive Interference happens when waves combine to form a wave that has a greater amplitude than the original waves had.

• Destructive Interference happens when waves combine to form a wave that has a smaller amplitude than the original waves had.


Interference, continued

• The image below shows what happens when light combines by interference.


Light and Matter

• When light strikes any form of matter, it can be reflected, absorbed, or transmitted.

• Reflection happens when light bounces off an object. • Absorption is the transfer of light energy to matter.• Transmission is the passing of light through matter.


Light and Matter, continued

• Transparent is matter through which light is easily transmitted. Glass is transparent.

• Translucent matter transmits light but also scatters it. Frosted windows are translucent.

• Opaque matter does not transmit any light. Computers and books are opaque.


Light and Matter, continued

• The images below explain the difference between the terms transparent, translucent, and opaque.


Colors of Objects

• Humans see different wavelengths of light as different colors.

• The color that an object appears to be is determined by the wavelengths of light that reach your eyes.

• Light reaches your eyes after being reflected off an object or after being transmitted through an object.


Colors of Objects, continued

• Colors of Opaque Objects When white light strikes a colored opaque object, some colors of light are absorbed, and some are reflected.

• Only the light that is reflected reaches your eyes and is detected. So, the colors of light that are reflected by an opaque object determine the color you see.


Colors of Objects, continued

• Colors of Transparent and Translucent Objects Ordinary window glass is colorless in white light because it transmits all the colors of light that strike it. But some transparent objects are colored.

• When you look through colored transparent or translucent objects, you see the color of light that was transmitted through the material.


Mixing Colors of Light

• Red, blue, and green are the primary colors of light. These three colors can be combined in different ratios to produce white light and many colors of light.

• Color Addition is combining colors of light.

• Light and Color Television The colors on a color TV are produced by color addition of the primary colors of light.


Mixing Colors of Pigment

• Pigments and Color A material that gives a substance its color by absorbing some colors of light and reflecting others is a pigment.

• Color Subtraction When you mix pigments together, more colors of light are absorbed or taken away. So, mixing pigments is called color subtraction.

• Yellow, cyan, and magenta are the primary pigments.

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