Conceptual Physical Science 5th Edition Chapter 11: LIGHT © 2012 Pearson Education, Inc.

This lecture will help you understand: Electromagnetic Spectrum Transparent and Opaque Materials Reflection Refraction Color Dispersion Polarization

Electromagnetic Nature of Light electromagnetic waves created by vibrating electric charges having frequencies that fall within the range of sight frequency of vibrating electrons equals the frequency of the light travels nearly a million times faster than sound in air light and all electromagnetic waves are transverse waves

Electromagnetic Spectrum Electromagnetic wave made up of vibrating electric and magnetic fields that regenerate each other by electromagnetic induction

Electromagnetic Spectrum The Electromagnetic Spectrum

Electromagnetic Spectrum CHECK YOUR NEIGHBOR The electromagnetic spectrum spans waves ranging from lowest to highest frequencies. The smallest portion of the electromagnetic spectrum is that of A. radio waves. microwaves. visible light. gamma rays. C. visible light.

Electromagnetic Spectrum CHECK YOUR ANSWER The electromagnetic spectrum spans waves ranging from lowest to highest frequencies. The smallest portion of the electromagnetic spectrum is that of A. radio waves. microwaves. visible light. gamma rays. Explanation: This can be inferred by a careful study of the spectrum and its regions in Figure 11.3. C. visible light.

Electromagnetic Nature of Light Order of increasing frequency of visible light: red violet—nearly twice the frequency of red ultraviolet—cause of sunburns X-rays gamma rays

Electromagnetic Nature of Light A situation to ponder… A photographer wishes to photograph a lightning bolt by setting a camera so that it is triggered by the sound of thunder. Put the correct answer here including the letter designation.

Is this a good idea or a poor idea? A situation to ponder… CHECK YOUR NEIGHBOR Is this a good idea or a poor idea? A. Good idea for nearby lightning strikes. Good idea for all strikes. Poor idea for nearby lightning strikes. Poor idea for all strikes. D. Poor idea for all strikes.

Is this a good idea or a poor idea? A situation to ponder… CHECK YOUR ANSWER Is this a good idea or a poor idea? A. Good idea for nearby lightning strikes. Good idea for all strikes. Poor idea for nearby lightning strikes. Poor idea for all strikes. Explanation: Light travels about a million times faster than sound. By the time the sound of thunder arrives, the lightning bolt is long gone. D. Poor idea for all strikes.

Transparent and Opaque Materials colored glass is opaque to much of incident white light

Transparent and Opaque Materials Light incident on: dry surfaces bounces directly to your eye wet surfaces bounces inside the transparent wet region, absorbing energy with each bounce, and reaches your eye darker than from a dry surface

Transparent and Opaque Materials Light is transmitted similar to sound light incident on matter forces some electrons in matter to vibrate

Transparent and Opaque Materials How light penetrates a pane of glass electrons in atoms of glass are forced into vibration energy is momentarily absorbed and vibrates electrons in the glass a vibrating electron either emits a photon or transfers the energy as heat light slows due to time delay between absorption and reemission of photons

Transparent and Opaque Materials Average speed of light through different materials vacuum—c (300,000,000 m/s) atmosphere—slightly less than c (but rounded off to c) water—0.75 c glass—0.67 c, depending on material diamond—0.41 c

Strictly speaking, the photons of light incident on glass are Transparent and Opaque Materials CHECK YOUR NEIGHBOR Strictly speaking, the photons of light incident on glass are A. also the ones that travel through and exit the other side. not the ones that travel through and exit the other side. absorbed and transformed to thermal energy. diffracted. B. not the ones that travel through and exit the other side.

Strictly speaking, the photons of light incident on glass are Transparent and Opaque Materials CHECK YOUR ANSWER Strictly speaking, the photons of light incident on glass are A. also the ones that travel through and exit the other side. not the ones that travel through and exit the other side. absorbed and transformed to thermal energy. diffracted. Explanation: Figure 11.6 illustrates this nicely. A photon that exits the glass is not the same photon that began the process of absorption and re-emission. B. not the ones that travel through and exit the other side.

Reflection Reflection: the returning of a wave to the medium through which it came when encountering a reflective surface Law of reflection: angle of incidence = angle of reflection

Reflection Virtual image same size as object, formed behind a mirror, and located at the position where the extended reflected rays converge as far behind the mirror as the object is in front of the mirror

Reflection Plane mirror note, the only axis reversed in an image is the front-back axis

Reflection Curved mirrors form a different virtual image convex mirror (that curves outward): virtual image is smaller and closer to the mirror than the object concave mirror (that curves inward): virtual image is larger and farther away than the object

Reflection Diffuse reflection light striking a rough or irregular surface reflects in many directions an undesirable circumstance is the ghost image that occurs on a non-cable TV set when TV signals bounce off buildings and other obstructions

Diffuse Reflection Application The open-mesh parabolic dish is a diffuse reflector for short-wavelength light. It is also a polished reflector for long-wavelength radio waves.

Diffuse Reflection Different road surfaces determine amount of diffuse reflection Rough road surface—diffuse reflection of illumination from your car headlights lets you see road ahead at night Wet road surface is smooth—more plane mirror than diffuse, so seeing road ahead is more difficult Now you know!

When you stand 2 meters in front of a plane mirror, your image is Reflection CHECK YOUR NEIGHBOR When you stand 2 meters in front of a plane mirror, your image is A. 2 meters in back of the mirror. 4 meters from you. Both A and B. None of the above. C. Both A and B.

When you stand 2 meters in front of a plane mirror, your image is Reflection CHECK YOUR ANSWER When you stand 2 meters in front of a plane mirror, your image is A. 2 meters in back of the mirror. 4 meters from you. Both A and B. None of the above. C. Both A and B.

Refraction Refraction bending of light when it passes from one medium to another caused by change in speed of light

Refraction Here we see light rays pass from air into water and from water into air pathways are reversible for both reflection and refraction

Refracted light that bends toward the normal is light that has Refraction CHECK YOUR NEIGHBOR Refracted light that bends toward the normal is light that has A. slowed down. sped up. nearly been absorbed. diffracted. A. slowed down.

Refracted light that bends toward the normal is light that has Refraction CHECK YOUR ANSWER Refracted light that bends toward the normal is light that has A. slowed down. sped up. nearly been absorbed. diffracted. A. slowed down.

Refracted light that bends away from the normal is light that has Refraction CHECK YOUR NEIGHBOR Refracted light that bends away from the normal is light that has A. slowed down. sped up. nearly been absorbed. diffracted. B. sped up

Refracted light that bends away from the normal is light that has Refraction CHECK YOUR ANSWER Refracted light that bends away from the normal is light that has A. slowed down. sped up. nearly been absorbed. diffracted. Explanation: This question is a consistency check with the question that asks about light bending toward the normal when slowing. B. sped up.

Refraction Illusions caused by refraction Objects submerged in water appear closer to the surface.

Refraction Illusions caused by refraction (continued) Objects such as the Sun seen through air are displaced because of atmospheric refraction.

Refraction Illusions caused by refraction (continued) Atmospheric refraction is the cause of mirages.

Refraction CHECK YOUR NEIGHBOR Which of these would not exist if light didn’t slow in transparent materials? A. Rainbows. Mirages. Magnifying glasses. All wouldn’t be. D. All wouldn’t be.

Refraction CHECK YOUR ANSWER Which of these would not exist if light didn’t slow in transparent materials? A. Rainbows. Mirages. Magnifying glasses. All wouldn’t be. D. All wouldn’t be.

Color Color we see depends on frequency of light ranging from lowest (red) to highest (violet). In between are colors of the rainbow. Hues in seven colors: red, orange, yellow, green, blue, indigo, and violet. Grouped together, they add to appear white.

Color Most objects don’t emit light, but reflect light. Selective Reflection Most objects don’t emit light, but reflect light. A material may absorb some of the light and reflect the rest. Selective Transmission The color of a transparent object depends on the color of the light it transmits.

Color Mixed Color Lights Three types of cone receptors in our eyes perceive color—each stimulated by only certain frequencies of light: lower-frequency light stimulate cones sensitive to low frequencies (red) Middle-frequency light stimulate cones sensitive to mid-frequencies (green) High-frequency light stimulate cones sensitive to high frequencies (blue) Stimulation of all three cones equally, we see white light

Color Additive primary colors (red, blue, green): red + blue = magenta red + green = yellow blue + green = cyan

Color Opposites of primary colors: opposite of green is magenta opposite of red is cyan opposite of blue is yellow The addition of any color to its opposite color results in white.

Dispersion Dispersion process of separation of light into colors arranged by frequency Components of white light are dispersed in a prism (and also in a diffraction grating)

When white light passes through a prism, green light is bent more than Dispersion CHECK YOUR NEIGHBOR When white light passes through a prism, green light is bent more than A. blue light. violet light. red light. None of the above. C. red light.

When white light passes through a prism, green light is bent more than Dispersion CHECK YOUR ANSWER When white light passes through a prism, green light is bent more than A. blue light. violet light. red light. None of the above C. red light.

Dispersion Rainbows a colorful example of dispersion

Dispersion Rainbow detail

Dispersion Rainbow facts an observer is in a position to see only a single color from any one droplet of water your rainbow is slightly different from the rainbow seen by others your rainbow moves with you disk within the bow is brighter because of overlapping of multiple refractions (which don’t occur outside the disk)

Dispersion Rainbow facts (continued) secondary rainbow is fainter (due to two internal reflections and refracted light loss). secondary bow is reversed in color (due to the extra internal reflection)

Compared with the primary rainbow, the secondary bow Dispersion CHECK YOUR NEIGHBOR Compared with the primary rainbow, the secondary bow A. is dimmer. has colors reversed. is caused by two internal reflections. All of the above. D. All of the above.

Compared with the primary rainbow, the secondary bow Dispersion CHECK YOUR ANSWER Compared with the primary rainbow, the secondary bow A. is dimmer. has colors reversed. is caused by two internal reflections. All of the above. D. All of the above.

Polarization Polarization alignment of transverse electric vectors in electromagnetic waves property of transverse waves Left: E & M wave is polarized Right: rope vibrations are polarized In both cases, wave is in the same plane as the plane of vibration.

Polarization Unpolarized light vibrations producing light are in random directions

Polarization Polarized light Unpolarized light divided into two internal beams polarized at right angles to each other. One beam is absorbed while the other beam is transmitted.

Polarization Polarized light (continued) Use your knowledge of vectors and vector components to explain how light that can’t pass through a pair of Polaroids at right angles to each other will pass light when a third Polaroid is sandwiched between them!

Polarization occurs for waves that are CHECK YOUR NEIGHBOR Polarization occurs for waves that are A. transverse. longitudinal. Both A and B. Neither A nor B. A. transverse.

Polarization occurs for waves that are CHECK YOUR ANSWER Polarization occurs for waves that are A. transverse. longitudinal. Both A and B. Neither A nor B. A. transverse.