chapter 22 properties of light. section 1: objectives describe light as an electromagnetic wave....

Chapter 22 Properties of Light

Section 1: Objectives Describe light as an electromagnetic wave. Calculate distances traveled by light by using the speed of light. Explain why light from the sun is important.

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

Figure 1: Electromagnetic Waves

Light: An Electromagnetic Wave An electric field surrounds every charged object. You see the effect of electric fields whenever you see objects stuck together by static electricity. A magnetic field surrounds every magnet. Because of magnetic fields, paper clips and iron filings are pulled toward magnets.

Light: An Electromagnetic Wave An EM wave can be produced by the vibration of an electrically charged particle. This vibration makes electric and magnetic fields vibrate also. Together, the vibrating fields are an EM wave that carries energy. The transfer of energy as electromagnetic waves is called radiation.

Light: An Electromagnetic Wave 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.

Calculating Speed

Example # 1 The distance from the sun to Venus is 108,000,000 km. Calculate the amount of time it takes for light to travel that distance. Speed = Distance / Time Speed of light = 300,000 km/s

Example # 2 The distance from the sun to Mercury is 83,000,000 km. Calculate the amount of time it takes for light to travel that distance. Speed = Distance / Time Speed of light = 300,000 km/s

Light: An Electromagnetic Wave EM waves from the sun are the major source of energy on Earth. For example, plants use photosynthesis to store energy from the sun. Animals use and store energy by eating plants or by eating other animals that eat plants.

Light: An Electromagnetic Wave 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.

Chapter 22 Section 1 Recap 1) In what for of energy does light travel? 2) How does light differ from other types of waves? 3) What type of wave is light? 4) What is the difference between an electric and magnetic field? 5) List 1 example of how you can observe an electric field.

Chapter 22 Section 1 Recap 6) How can an EM wave be produced? 7) What 2 vibrating fields make up an EM wave? 8) ___________ is the speed of light. 9) What is the major source of energy for the sun? 10) List 1 way animals get energy indirectly from the sun.

Chapter 22 Section 1 Recap 11) How are fossil fuels formed? 12) In which direction do EM waves travel away from the sun? 13) From Figure 1, where is the electric field located in relation to the magnetic field? 14) From Figure 1, does the magnetic field vibrate vertically or horizontally? 15) From Figure 1, does the electric field vibrate vertically or horizontally?

Chapter 22 Section 1 Recap 16) Calculate the time it takes for light to travel between 2 objects which are 912 km apart. 17) Calculate the time it takes for light 2 travel between 2 mountain ranges which are 233.1 km apart. 18) Calculate the time it takes for light to travel between 2 vehicles which are 155.1 km apart.

Section 2: Objectives Identify how electromagnetic waves differ from each other. Describe some uses for radio waves and microwaves. List examples of how infrared waves and visible light are important in your life. Explain how ultraviolet light, X rays, and gamma rays can be both helpful and harmful.

Characteristics of EM Waves The light that you can see is called visible light. However, there is light that you cant see. The light that you can see and light that you cannot 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.

Characteristics of EM Waves 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.

The EM Spectrum: Figure 1

Characteristics of EM 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.

Characteristics of EM Waves 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.

Characteristics of EM 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.

Characteristics of EM Waves 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. The signals then travel through cables to TVs in homes.

Characteristics of EM Waves Microwaves have shorter wavelengths and higher frequencies than radio waves. Microwaves have wavelengths between 1 mm and 30 cm.

Microwaves: Figure 2

Characteristics of EM Waves Microwaves are used to send information over long distances. Cell phones send and receive signals using microwaves. Signals sent between Earth and artificial satellites in space are also carried by microwaves.

Characteristics of EM Waves 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.

Characteristics of EM 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 give off infrared waves, including the sun, buildings, trees, and your body. The amount of infrared waves an object emits depends on the objects temperature. Warmer objects give off more infrared waves than cooler objects.

Characteristics of EM Waves 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.

Characteristics of EM Waves 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.

Characteristics of EM Waves 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.

Characteristics of EM Waves Too much UV light can cause sunburn. UV light can also cause skin cancer and wrinkles, and damage the eyes. 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.

Characteristics of EM Waves 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.

X-Rays: Figure 3

Characteristics of EM Waves 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.

Chapter 22 Section 2 Recap 1) What type of wave is visible light? 2) What type of wave is non-visible light? 3) How is the EM spectrum divided into regions? 4)From Figure 1, which type of wave has the lowest frequency? 5) From Figure 1, which type of wave has the lowest wavelength?

Chapter 22 Section 2 Recap 6) From Figure 1, which type of wave has the highest wavelength? 7) From Figure 1, which type of wave has the highest frequency? 8) What is modulation? 9) What do AM and FM stand for? 10) Why do AM waves travel farther than FM waves?

Chapter 22 Section 2 Recap 11) Which type of waves carry TV signals? 12) From Figure 2, what is a magnetron? 13) What 2 things are radars used to detect? 14) What does the amount of infrared waves an object emits depend on? 15) List 1 example of an object that emits white light.

Chapter 22 Section 2 Recap 16) What is white light? 17) Where are the longest wavelengths seen? 18) Where are the shortest wavelengths seen? 19) What is the visible spectrum? 20) Which type of rays are used to kill harmful bacteria in food and can penetrate most materials easily?

Section 3: Objectives Describe how reflection allows you to see things. Describe absorption and scattering. Explain how refraction can create optical illusions and separate white light into colors.

Section 3: Objectives Explain the relationship between diffraction and wavelength. Compare constructive and destructive interference of light.

Reflection, Refraction, and Interference 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. This law is explained on the next slide.

Reflection, Refraction, and Interference 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, Refraction, and Interference 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.

Law of Reflection: Figure 1

Reflection, Refraction, and Interference 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.

Reflection, Refraction, and Interference 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 lights energy. As a result, the beam of light becomes dim.

Reflection, Refraction, and Interference 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.

Reflection, Refraction, and Interference 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.

Reflection, Refraction, and Interference 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.

Reflection, Refraction, and Interference Your brain always interprets light as traveling in straight lines. But when you look at an object that is underwater, the light reflecting off the object does not travel in a straight line. Instead, it refracts.

Refraction Diagram: Figure 3 Because of refraction, the cat and the fish see optical illusions.

Reflection, Refraction, and Interference 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.

Reflection, Refraction, and Interference: Figure 4 Waves with short wavelengths bend more than waves with long wavelengths. White light can be separated into different colors during refraction, as shown below.

Reflection, Refraction, and Interference 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.

Reflection, Refraction, and Interference 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.

Reflection, Refraction, and 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.

Reflection, Refraction, and Interference: Figure 5 The image below shows what happens when light combines by interference.

Chapter 22 Section 3 Recap 1) What does the law of reflection state? 2) What is the difference between regular and diffuse reflection? 3) From Figure 1, what is the difference between angle of incidence and angle of reflection? 4) What happens when a beam of light shines through the air? 5) T/F Light can be scattered out of a beam by air particles.

Chapter 22 Section 3 Recap 6) What is a lens? 7) How does your brain always interpret light? 8) What is white light composed of? 9) What does the amount a wave diffracts depend on? 10) What size is the wavelength of visible light?

Section 4: Objectives Name and describe three ways light interacts with matter. Explain how the color of an object is determined. Explain why mixing colors of light is called color addition. Describe why mixing colors of pigment is called color subtraction.

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: Figure 1 The image below explains transmission, reflection, and absorption.

Light and Matter 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.

Light and Matter: Figure 2 The images below explain the difference between the terms transparent, translucent, and opaque.

Light and Matter 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.

Light and Matter 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.

Light and Matter 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.

Light and Matter 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.

Light and Matter 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.

Light and Matter: Figure 3

Chapter 22 Section 4 Recap 1) What is the difference between reflection and absorption? 2) Give 1 example of an object that is transparent. 3) Give 1 example of an object that is translucent. 4) Give 1 example of an object that is opaque. 5) What happens when white light strikes a colored opaque object?

Chapter 22 Section 4 Recap 6) Why is ordinary window glass colorless in white light? 7) List the 3 primary colors of light. 8) List the 3 primary pigments. 9) From Figure 3, what color is produced when green and blue mix together? 10) From Figure 3, what color is produced when magenta and yellow mix together?

chapter 22 properties of light. section 1: objectives describe light as an electromagnetic wave....

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