The Nature of Light

1. The Nature of Light Chapter 22 Preview Section 1 What Is Light? Section 2 The Electromagnetic Spectrum Section 3 Interactions of Light Waves Section 4 Light and Color Concept Mapping

2. Chapter 22 Section1 What Is Light? Bellringer What do you think light is? Is light made of matter? Can light travel through space? Explain your answers in your science journal.

3. Chapter 22 Section1 What Is Light? 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.

4. Chapter 22 Section1 What Is Light? 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.

5. Chapter 22 Section1 What Is Light?

6. Chapter 22 Section1 What Is Light? Light: An Electromagnetic Wave, continued • 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. • A magnetic field surrounds every magnet. Because of magnetic fields, paper clips and iron filings are pulled toward magnets.

7. Chapter 22 Section1 What Is Light? Light: An Electromagnetic Wave, continued • How EM Waves Are Produced 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.

8. Chapter 22 Section1 What Is Light? 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.

9. Chapter 22 Section1 What Is Light?

10. Chapter 22 Section1 What Is Light? 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. • Animals use and store energy by eating plants or by eating other animals that eat plants.

11. Chapter 22 Section1 What Is Light? 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.

12. Chapter 22 Section2 The Electromagnetic Spectrum Bellringer Describe the weather conditions necessary to see a rainbow. Why do rainbows form? Write your answers in your science journal.

13. Chapter 22 Section2 The Electromagnetic Spectrum 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.

14. Chapter 22 Section2 The Electromagnetic Spectrum Characteristics of EM Waves • 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 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.

15. Chapter 22 Section2 The Electromagnetic Spectrum 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.

16. Chapter 22 Section2 The Electromagnetic Spectrum

17. Chapter 22 Section2 The Electromagnetic Spectrum 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.

18. Chapter 22 Section2 The Electromagnetic Spectrum 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.”

19. Chapter 22 Section2 The Electromagnetic Spectrum Radio Waves, continued • 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.

20. Chapter 22 Section2 The Electromagnetic Spectrum Radio Waves, continued • 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.

21. Chapter 22 Section2 The Electromagnetic Spectrum Microwaves • Microwaves have shorter wavelengths and higher frequencies than radio waves. Microwaves have wavelengths between 1 mm and 30 cm.

22. Chapter 22 Section2 The Electromagnetic Spectrum

23. Chapter 22 Section2 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.

24. Chapter 22 Section2 The Electromagnetic Spectrum 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.

25. Chapter 22 Section2 The Electromagnetic Spectrum 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 give 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.

26. Chapter 22 Section2 The Electromagnetic Spectrum 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.

27. Chapter 22 Section2 The Electromagnetic Spectrum 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.

28. Chapter 22 Section2 The Electromagnetic Spectrum 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.

29. Chapter 22 Section2 The Electromagnetic Spectrum 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.

30. Chapter 22 Section2 The Electromagnetic Spectrum 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.

31. Chapter 22 Section2 The Electromagnetic Spectrum

32. Chapter 22 Section2 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.

33. Chapter 22 Section3 Interactions of Light Waves Bellringer Mirrors are common objects that most people use every day. From your experience, how do mirrors work and what do mirrors do to light waves? Explain your answers in your science journal.

34. Chapter 22 Section3 Interactions of Light Waves 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.

35. Chapter 22 Section3 Interactions of Light Waves Objectives, continued • Explain the relationship between diffraction and wavelength. • Compare constructive and destructive interference of light.

36. Chapter 22 Section3 Interactions of Light Waves 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. • This law is explained on the next slide.

37. Chapter 22 Section3 Interactions of Light Waves Law of Reflection Click below to watch the Visual Concept. Visual Concept

38. Chapter 22 Section3 Interactions of Light Waves Reflection, continued • Types ofReflection 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.

39. Chapter 22 Section3 Interactions of Light Waves 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.

40. Chapter 22 Section3 Interactions of Light Waves

41. Chapter 22 Section3 Interactions of Light Waves Reflection, continued • Light Source orReflection? 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.

42. Chapter 22 Section3 Interactions of Light Waves 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.

43. Chapter 22 Section3 Interactions of Light Waves Absorption and Scattering, continued • 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. • 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.

44. Chapter 22 Section3 Interactions of Light Waves 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.

45. Chapter 22 Section3 Interactions of Light Waves 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.

46. Chapter 22 Section3 Interactions of Light Waves Refraction, continued • 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.

47. Chapter 22 Section3 Interactions of Light Waves Refraction, continued • Because of refraction, the cat and the fish see optical illusions.

48. Chapter 22 Section3 Interactions of Light Waves Refraction, continued • Refraction and Color SeparationWhite 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.

49. Chapter 22 Section3 Interactions of Light Waves Refraction, continued • Waves with short wavelengths bend more than waves with long wavelengths. • White light can be separated into different colors during refraction, as shown below.

50. Chapter 22 Section3 Interactions of Light Waves Diffraction • Diffractionis 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.