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Section 1 What Is Light?

1. What is Light? What are some things that produce light?

2-3. 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.

• Light is an electromagnetic wave (EM wave).

Chapter 22


Teacher Notes:How to add video clips to Power Point Presentations. 1. Log into streaming.discoveryeducation.com (Ask your Media Specialist for your password if you don’t have it) 2. Type topic into search box, choose DE streaming, video segment, 6-8 3. Look for videos created after 2000. When you find a segment you like, check the box and then click on the download picture. Sometimes a video will not download. Try using Firefox as your browser. Name the video what it is about so that you know which slide to insert. Save it in the same folder as the power point. 4. Insert it into power point. Drag the corner to make it as big as you’d like


The nature of light 4min


Section 1 What Is Light?Chapter 22

4-5. An electromagnetic wave is a wave that consists of electric and magnetic fields that vibrate at right angles to each other.



6-8. Light: An Electromagnetic Wave• Electric and Magnetic Fields An electric field surrounds every charged object. You see the effect of electric fields whenever you see objects stuck together by static electricity.

•An electric field attracts oppositely charged objects around it and repels like-charged objects.

• A magnetic field surrounds every magnet. Because of magnetic fields, paper clips and iron filings are pulled toward magnets.

Chapter 22


Teacher Notes:

How to insert animations from the online textbook Holt.1. Log in at my.hrw.com2. Click on Chapter 21, click on the eactivities red tab on the top3. Choose the animation. 4. The word “file” should be in the top of the box. (If “file” is not there, go to Firefox and try again)5. Click on “file”, then “save as” and save to the same folder that has the PPT6. Click on insert, choose object and go to the file to insert it. 7. You may have to hyperlink the object back to the file.

Contact [email protected] for more information



9. How EM Waves Are Produced When electrically charged particle vibrates, electric and magnetic fields vibrate also to create an EM wave which carries energy.

10. The transfer of energy as electromagnetic waves is called radiation. (sometimes called electromagnetic radiation)

Chapter 22

Visual Concepts-EM wave.mht


11. Thunder and lightning are produced at the same time. But you usually see lightning before you hear thunder, because light travels much faster than sound.

http://www.wikihow.com/Calculate-the-Distance-from-Lightning



12. The Speed of Light

• Scientists have yet to discover anything that travels faster than light.

• In the near vacuum of space, the speed of light is about 300,000 km/s. Light travels slightly slower in air, glass, and other types of matter. (186,000miles/sec)

Chapter 22


The speed of light 4 min


13. Even though light travels quickly, it takes about 8.3 min. for light to travel from the sun to the earth because earth is 150,000,000 km away.



14. Light from the Sun

• EM waves from the sun are the major source of energy on Earth. For example, plants use photosynthesis to store energy from the sun.

• What are other ways that energy is used from the sun on the earth?

Chapter 22

-our bodies make Vitamin D from the sun-solar power for energy-help us see-keep us warm



15-16. Light from the Sun, continued• Even fossil fuels store energy from the sun. Fossil fuels are formed from the remains of plants and animals that lived millions of years ago.

• Only a very small part of the total energy given off by the sun reaches Earth. The sun gives off energy as EM waves in all directions. Most of this energy travels away in space.

•16. because the earth is so small compared to the sun

Chapter 22


Characteristics of EM Waves•1. EM waves are disturbances which move through matter or empty space as an electric force field. •The light that you can see is called visible light. However, there is light that you can’t see.

• The light that you can see and light that you cannot see are both kinds of electromagnetic (EM) waves. Other kinds of EM waves include X rays, radio waves, and microwaves.

• All EM waves travel at 300,000 km/s in a vacuum.

Section 2 The Electromagnetic SpectrumChapter 22


EM spectrum 2 min


Characteristics of EM Waves, continued

• The entire range of EM waves is called the electromagnetic spectrum. The electromagnetic spectrum is divided into regions according to the length of the waves.

• The electromagnetic spectrum is shown on the next slide. Check your drawing on the inside of your booklet cover to be sure you have everything




2. Gamma rays are the waves with the shortest wavelength and radio waves have the longest wavelength.

3.

Arranged from long to short wavelength, and low to high frequency


4. An electron’s motion depends on both the force on the electron and its velocity, which are often in different directions.

5. The charge creates a force field in the empty space around an atom. A postitively charged atom will attract a negatively charged atom.

6. Electromagnetic waves are produced by the vibration of an electric field and a magnetic field together.

The electromagnetic spectrum is the entire range of EM waves.


EM waves 3 min.


8. F 9. E & D 10. E 11. C 12. E 13. C 14. A 15. B

16. A 17. C 18. A 19. A 20. D 21. C 22. G 23. B & C

24. D 25. F 26. G 27. E


Radio Waves

• Radio waves cover a wide range of waves in the EM spectrum. Radio waves have some of the longest wavelengths and the lowest frequencies of all EM waves.

• Radio waves are any EM waves that have wavelengths longer than 30 cm. Radio waves are used for broadcasting radio signals.



Radio Waves, continued

• Broadcasting Radio Signals Radio stations can encode sound information into radio waves by varying either the waves’ amplitude or frequency.

• Changing amplitude or frequency of a wave is called modulation. AM stands for “amplitude modulation, and FM stands for “frequency modulation.”


Visual Concepts AM-FM.mht



• Comparing AM and FM Radio Waves AM radio waves have longer wavelengths than FM radio waves. AM radio waves can bounce off the atmosphere and thus can travel farther than FM radio waves.

• But FM radio waves are less affected by electrical noise than AM radio waves, so music broadcast from FM sounds better than music from AM stations.




• Radio Waves and Television TV signals are also carried by radio waves. Most TV stations broadcast radio waves that have shorter wavelengths and higher frequencies than those from radio stations.

• Some waves carrying TV signals are transmitted to artificial satellites orbiting Earth. The waves are amplified and sent to ground antennas. They the signals travel through cables to TVs in homes.



Microwaves• Microwaves have shorter wavelengths and higher frequencies than radio waves. Microwaves have wavelengths between 1 mm and 30 cm.



Chapter 22 Section 2 The Electromagnetic Spectrum


Microwaves, continued

• Microwaves and Communication Microwaves are used to send information over long distances.

• Cellular phones send and receive signals using microwaves. Signals sent between Earth and artificial satellites in space are also carried by microwaves.


http://urbanlegends.about.com/b/2008/07/09/cell-phone-popcorn-trick-revealed.htm


Microwaves, continued

• Radar Microwaves are used in radar. Radar (radio detection and ranging) is used to detect the speed and location of objects.

• Radar sends out microwaves that reflect off an object and return to the transmitter. The reflected waves are used to calculate speed.



Infrared Waves• Infrared waves have shorter wavelengths and higher frequencies than microwaves. The wavelengths of infrared waves vary between 700 nanometers (nm) and 1 mm.

• Almost everything gives off infrared waves, including the sun, buildings, trees, and your body. The amount of infrared waves an object emits depends on the object’s temperature. Warmer objects give off more infrared waves than cooler objects.•Military Weapon http://www.cbsnews.com/video/watch/?id=3897986n



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.

• The visible light from the sun is white light. White light is visible light of all wavelengths combined.



• 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.

•Why we see colors


Visual Concepts why we see colors.mht


Ultraviolet Light• Ultraviolet light (UV light) is another type of EM wave produced by the sun. Ultraviolet waves have shorter wavelengths and higher frequencies than visible light.

• The wavelengths of UV light wave vary between 60 nm and 400 nm.



Ultraviolet Light, continued

• Bad Effects Too much UV light can cause sunburn. UV light can also cause skin cancer and wrinkles, and damage the eyes.

• Good Effects Ultraviolet waves produced by UV lamps are used to kill bacteria on food and surgical tools. Small amounts of UV light are beneficial to your body, causing skin cells to produce vitamin D.



X Rays and Gamma Rays

• X Rays have wavelengths between 0.001 nm and 60 nm. X rays can pass through many materials, making them useful in the medical field.

• However, too much exposure to X rays can damage or kill living cells.



Chapter 22 Section 2 The Electromagnetic Spectrum


X Rays and Gamma Rays, continued

• Gamma Rays have wavelengths shorter than 0.1 nm. They can penetrate most materials easily.

• Gammas rays are used to treat some forms of cancer. Doctors focus the rays on tumors inside the body to kill the cancer cells.

• Gamma rays are also used to kill harmful bacteria in foods, such as meat and fresh fruits.



and decreasing ____________________________.


H.W.-Warm-up #1- Compare and contrast sound waves and light waves.

-can travel through a medium or empty space

-waves that transfer energy-Can travel through matter-reflection, refraction, etc

-speed of sound-343 m/s

Light Waves Sound Waves

-transverse waves-longitudinal waves

-can only travel through a medium

-can see some of them -can’t see them

-speed of light-300,000,000 m/s

-speed up when they travel through solids and liquids

-slow down when they pass through solids and liquids


A review of light waves.


Answers to Lab Stations

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

Who can explain the angle of incidence and the angle of reflection?

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

• This law is explained on the next slide.

Chapter 22 Section 3 Interactions of Light Waves


Reflection, continued

• Types 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.



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.



Section 3 Interactions of Light WavesChapter 22


Reflection, continued• D. Light Source or Reflection? The tail of a firefly, flames, light bulbs, and the sun are light sources . They are called luminous. 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.



Refraction

•1.A 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

• Refraction and Lenses 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.



Investigating Color

When “white light” enters a prism, it slows down and bends. Each color has a different wavelength so they bend at different angles. When the waves leave the prism and go back into the air, they bend again and we can see them.


Diffraction

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

•2. 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.



• 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.

Use the diffraction glasses to look at different light sources.

Polarized lenses allow light to pass through slits and control the amount of light that reaches your eyes.



How do polarized sunglasses work?

When you go outside, light is traveling in all directions, reflecting off of many surfaces. Polarized sunglasses have two lenses with slits in them which allow light to travel in only one direction to your eyes. The amount of diffracted light depends on how well the slits line up. If the slits are perpendicular to each other, then the light cannot pass through the lenses.Some sunglasses also block out harmful UV rays from the sun. When you put on sunglasses, your pupils open up and allow more light to pass into your eyes. That is why you need to wear sunglasses with UV protection.


Interference, continued

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



Interference

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

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

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



Absorption and Scattering• 1. Absorption of Light The transfer of energy carried by light waves is called absorption.

• 2. 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• 3. Scattering of Light 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.

• The sky is blue because the short light waves (blue) are scattered while the longer light waves pass through the atmosphere.

•Light Transmission .


Visual Concepts transmission.mht


Section 4 Light and Color

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.

Chapter 22



Light and Matter, continued

• The image at right explains transmission, reflection, and absorption.

Chapter 22




• Transparent matter is matter though 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.

Chapter 22




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

Chapter 22



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.

Chapter 22



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.

Chapter 22



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.

Chapter 22



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.

Chapter 22

Visual Concepts color addition.mht



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.

Chapter 22

Teacher notes: spin the color disk to show the colors combining to white.


Section 4 Light and ColorChapter 22

Visual Concepts color subtraction.mht


Mysterious Glowing Ball DemonstrationTurn on the ball, what color is it? Now spin the ball, why do you think this is happening?

When the ball is spun at different speeds, you can see the primary and secondary colors.

How does it work? There is an LED(light emitting diode) inside which rapidly flashes red, green and blue. The flash rate is so fast, the human eye cannot perceive the individual colors.


The Nature of LightChapter 22

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