1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Waves and Particles The two most commonly used models describe light either as a wave or as a stream of particles. Light produces interference patterns like water waves. Light can be modeled as a wave. This model describes light as transverse waves that do not require a medium in which to travel. Light waves are also called electromagnetic waves because they consist of changing electric and magnetic fields. Section 2 The Nature of Light Chapter 15

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Waves and Particles, continued The wave model of light explains much of the observed behavior of light. Light waves may reflect, refract, or diffract. Light waves also interfere with one another. The wave model of light cannot explain some observations. When light strikes a piece of metal, electrons may fly off the metal’s surface. Section 2 The Nature of Light Chapter 15

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Waves and Particles, continued Light can be modeled as a stream of particles. In the particle model of light, the energy of light is contained in packets called photons. A photon is a unit or quantum of light. A beam of light is considered to be a stream of photons. Photons do not have mass. The energy in a photon is located in a particular place. Section 2 The Nature of Light Chapter 15

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Waves and Particles, continued The model of light used depends on the situation. The energy of light is proportional to frequency. The speed of light depends on the medium. Section 2 The Nature of Light Chapter 15

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Nature of Light Chapter 15

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Waves and Particles, continued Section 2 The Nature of Light Chapter 15 The brightness of light depends on intensity. The quantity that measures the amount of light illuminating a surface is called intensity. Intensity is the rate at which energy flows through a given area of space. Like the intensity of sound, the intensity of light from a light source decreases as the light spreads out in spherical wave fronts.

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Nature of Light Chapter 15

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Electromagnetic Spectrum, continued The electromagnetic spectrum consists of light at all possible energies, frequencies, and wavelengths. Sunlight contains ultraviolet light. The invisible light that lies just beyond violet light falls into the ultraviolet (UV) portion of the spectrum. X rays and gamma rays are used in medicine. X rays have wavelengths less than 10 –8 m. The highest energy electromagnetic waves are gamma rays. Section 2 The Nature of Light Chapter 15

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Electromagnetic Spectrum, continued Infrared light can be felt as warmth. Infrared (IR) wavelengths are slightly longer than red light. Microwaves are used in cooking and communication. Microwaves have wavelengths in the range of centimeters. Radio waves are used in communications and radar. Radio waves have wavelengths that range from tenths of a meter to millions of meters. Air-traffic control towers use radar to determine the locations of aircraft. Radar, radio detection and ranging, is a system that uses reflected radio waves to determine the velocity and location of objects. Section 2 The Nature of Light Chapter 15

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reflection of Light Light can be modeled as a ray. A light ray a line in space that matches the direction of the flow of radiant energy. This model is used to describe reflection and refraction. The study of light in cases in which light behaves like a ray is called geometrical optics. Using light rays, one can trace the path of light in geometrical drawings called ray diagrams. Section 3 Reflection and Color Chapter 15

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reflection of Light, continued Rough surfaces reflect light rays in many directions. Such reflection of light into random directions is called diffuse reflection. Smooth surfaces reflect light rays in one direction Section 3 Reflection and Color Chapter 15

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reflection of Light, continued On smooth surfaces, the angle of the light rays reflecting off the surface is called the angle of reflection. The angle of incidence is the angle of the light rays striking the surface. The law of reflection states that the angle of incidence equals the angle of reflection. Section 3 Reflection and Color Chapter 15

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Reflection and Color When light hits a smooth surface, the angle of incidence (  ) equals the angle of reflection (  ′). Chapter 15

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mirrors Flat mirrors form virtual images by reflection. A virtual image is an image that forms at a location from which light rays appear to come but do not actually come. Section 3 Reflection and Color Chapter 15

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mirrors, continued Curved mirrors can distort images. Because the surface is not flat, the line perpendicular to the mirror (the normal) points in different directions for different parts of the mirror. Mirrors that bulge out are called convex mirrors. Indented mirrors are called concave mirrors. Concave mirrors can create real images. Concave mirrors are used to focus reflected light. A concave mirror can form a virtual image behind the mirror or a real image in front of the mirror. Section 3 Reflection and Color Chapter 15

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mirrors, continued A real image an image of an object formed by light rays that actually come together at a specific location. A real image results when light rays from a single point of an object are focused onto a single point or small area. Telescopes use curved surfaces to focus light. Section 3 Reflection and Color Chapter 15

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Seeing Colors The different wavelengths of visible light correspond to many of the colors that you perceive. Objects have color because they reflect certain wavelengths. White light from the sun actually contains light from the visible wavelengths of the electromagnetic spectrum. Colors may add or subtract to produce other colors. Section 3 Reflection and Color Chapter 15

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Reflection and Color Subtractive primary colors Red, green, and blue lights can combine to produce yellow, magenta, cyan, or white. Yellow, magenta, or cyan filters can combine to produce red, green, blue, or black. Additive primary colors Chapter 15

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Refraction of Light Light waves bend, or refract, when they pass from one medium to another. Light bends when it changes mediums because the speed of light is different in each medium. When light moves from a material in which its speed is higher to a material in which its speed is lower, the ray is bent toward the normal. If light moves from a material in which its speed is lower to one in which its speed is higher, the ray is bent away from the normal. Section 4 Refraction, Lenses, and Prisms Chapter 15

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Refraction Section 4 Refraction, Lenses, and Prisms Chapter 15

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Refraction of Light, continued Refraction makes objects appear to be in different positions. Refraction in the atmosphere creates mirages. A mirage is a virtual image. Light can be reflected at the boundary between two transparent mediums. If the angle at which light rays meet the boundary between two mediums becomes small enough, the rays will be reflected as if the boundary were a mirror. This angle is called the critical angle. This type of reflection is called total internal reflection. Section 4 Refraction, Lenses, and Prisms Chapter 15

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Refraction Section 4 Refraction, Lenses, and Prisms Chapter 15

23. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Total Internal Reflection Section 4 Refraction, Lenses, and Prisms Chapter 15

24. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Refraction of Light, continued Total internal reflection is the complete reflection that takes place within a substance when the angle of incidence of light striking the surface boundary is less than the critical angle. Fiber optics use total internal reflection. Section 4 Refraction, Lenses, and Prisms Chapter 15

25. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Lenses Lenses rely on refraction. A lens is a transparent object that refracts light waves such that they converge or diverge to create an image. A converging lens bends light inward. A converging lens can create either a virtual image or a real image. A diverging lens bends light outward. A diverging lens can only create a virtual image. Section 4 Refraction, Lenses, and Prisms Chapter 15

26. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Lenses, continued Lenses can magnify images. A magnifying glass is an example of a converging lens. Magnification is a change in the size of an image compared with the size of an object. By adjusting the height of the lens, you can focus the light rays together into a small area, called the focal point. Microscopes and refracting telescopes use multiple lenses. Section 4 Refraction, Lenses, and Prisms Chapter 15

27. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Refraction, Lenses, and Prisms A compound microscope uses several lens to produce a highly magnified image. Chapter 15

28. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Lenses, continued The eye depends on refraction and lenses. Light first enters the eye through a transparent tissue called the cornea. After the cornea, light passes through the pupil. Then, light travels through the lens. Muscles can adjust the curvature of the lens until an image is focused on the back layer of the eye, the retina. The retina is composed of tiny structures, called rods and cones, that are sensitive to light. Section 4 Refraction, Lenses, and Prisms Chapter 15

29. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Eye Section 4 Refraction, Lenses, and Prisms Chapter 15

30. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Dispersion and Prisms A prism is an optical system that consists of two or more plane surfaces of a transparent solid at an angle with each other. Different colors of light are refracted differently. Light separates into different colors because of differences in wave speed. In the visible spectrum, violet light travels the slowest and red light travels the fastest. In optics, dispersion is the process of separating a wave (such as white light) of different frequencies into its individual component waves (the different colors) Section 4 Refraction, Lenses, and Prisms Chapter 15