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Where do we get light? Slide 2 A luminous object is one that produces light. An illuminated object is one that reflects light. Luminous Objects Illuminated Objects Luminous and Illuminated Objects Slide 3 We see things because they reflect light into our eyes: Homework Slide 4 How does light behave? Slide 5 Reflection of Light Reflection occurs when a wave bounces back after striking a barrier. Example: a reflection in a mirror. Slide 6 Three things that affect how light is reflected: Surface of the Object Color of the Object Shape of the Object Slide 7 Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions Surface of the Object Slide 8 Slide 9 Slide 10 Ever notice that an asphalt driveway seems hotter on a summer day than a concrete sidewalk? This occurs because light that is not reflected from the surface of an object may be absorbed by the object and converted into thermal energy. Color of the Object Slide 11 Shape of the Object Reflection from a mirror: Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror Slide 12 The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at ____ _____ angle it hits it. The same !!! Slide 13 Slide 14 Types of Mirrors Plane (flat), Concave, & Convex Slide 15 Plane Mirrors Flat Surface Light is reflected straight back, resulting in an upright image that is the same size as the original object. Slide 16 Concave Mirrors Curves Inward (like the inside of a bowl) If an object is very close to the mirror, light is reflected in a way that an enlarged, upright image is produced. If the object is very far away, the image is reduced in size and upside down. Slide 17 Convex Mirrors Curves Outward Results in an image your eyes detect as upright and reduced in size. The side mirrors on cars are convex mirrors. (Objects in mirror are closer than they appear.) Slide 18 Slide 19 Refraction of Light Refraction is the bending of a wave as it passes from one medium to another. Slide 20 What causes the light to bend? Whats different about air and water? DENSITY the amount of mass in a certain volume of a substance (mass/volume) AIR WATER gas liquid Slide 21 Example of Refraction When a straw is placed in water it looks like this: In this case the light rays are slowed down by the water and are bent, causing the straw to look broken. The two mediums in this example are air and water. Slide 22 Another Example: When you use a magnifying glass, the object appears larger because of refraction. The light waves traveling in the air change direction when they enter the glass of the lens, and then again when they move from the glass back into the air again. Lens Slide 23 Diffraction of Light Diffraction is the bending, spreading, and interference of waves when they go through a narrow opening. Slide 24 Diffraction Patterns Radio waves can diffract around hills, mountains or even the whole planet. Light waves can diffract through tiny slits. X-rays can diffract around atoms. Slide 25 Electromagnetic waves have a huge range of wavelengths. If the wavelength is of a similar size to a gap in a harbor wall, then the wave will diffract as shown below. Slide 26 If the wavelength does not match the size of the gap, then only a little diffraction will occur at the edge of the wave. Slide 27 Transmission of Light Transmission is the passing of waves through a medium. Slide 28 Think about a radio station An electromagnetic wave is produced. The wave travels from the stations transmitter out in all directions at the speed of light. Even though you cannot hear radio waves when your radios turned off, the waves are still being transmitted in the room. Slide 29 What happens when light hits these objects? Glass of water School bus window Notebook paper Waxed paper Plastic wrap Tissue paper Cardboard Textbook Hand lens Slide 30 Many materials are classified by how well they transmit light. Three Types of Materials: Transparent Translucent Opaque Slide 31 Transparent A material that permits light to pass through Slide 32 Transparent objects: The windows on a school bus, A clear empty glass, A clear window pane, The lenses of some eyeglasses, Clear plastic wrap, The glass on a clock, A hand lens, Colored glass ALL of these are transparent. Yes, we can see through them because light passes through each of them. Slide 33 Translucent A material that transmits some light but also scatter light in all directions Slide 34 Translucent objects: Thin tissue paper, Waxed paper, Tinted car windows, Frosted glass, Clouds, All of these materials are translucent and allow some light to pass but the light cannot be clearly seen through. Slide 35 Opaque A material that allows no light to pass through Slide 36 Opaque objects: Heavy weight paper, Cardboard Aluminum foil, Mirror, bricks, buildings, Your eyelids and hands, Solid wood door, All of these objects are opaque because light cannot pass through them at all. They cast a dark shadow. Slide 37 Shadows Shadows are places where light is blocked: Rays of light