Hewitt suchocki hewitt conceptual physical science fourth edition
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Hewitt/Suchocki/Hewitt Conceptual Physical Science Fourth Edition. Chapter 11: LIGHT. This lecture will help you understand:. Electromagnetic Spectrum Transparent and Opaque Materials Reflection Refraction Color Dispersion Polarization. Electromagnetic Nature of Light. Light:

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Hewitt suchocki hewitt conceptual physical science fourth edition

Hewitt/Suchocki/HewittConceptual Physical Science Fourth Edition

Chapter 11:

LIGHT


This lecture will help you understand

This lecture will help you understand:

  • Electromagnetic Spectrum

  • Transparent and Opaque Materials

  • Reflection

  • Refraction

  • Color

  • Dispersion

  • Polarization


Electromagnetic nature of light

Electromagnetic Nature of Light

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 Spectrum

Electromagnetic wave

  • made up of vibrating electric and magnetic fields that regenerate each other by electromagnetic induction


Electromagnetic spectrum1

Electromagnetic Spectrum

The Electromagnetic Spectrum


Hewitt suchocki hewitt conceptual physical science fourth edition

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.


Hewitt suchocki hewitt conceptual physical science fourth edition

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.


Electromagnetic nature of light1

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


Hewitt suchocki hewitt conceptual physical science fourth edition

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.


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.


Is this a good idea or a poor idea1

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.


Transparent and opaque materials

Transparent and Opaque Materials

Opaque materials:

colored glass is opaque to much of incident white light


Transparent and opaque materials1

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 materials2

Transparent and Opaque Materials

Light is transmitted similar to sound

  • light incident on matter forces some electrons in matter to vibrate


Transparent and opaque materials3

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 materials4

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.


Strictly speaking the photons of light incident on glass are1

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.


Reflection

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


Reflection1

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


Reflection2

Reflection

Plane mirror

  • note, the only axis reversed in an image is the front-back axis


Reflection3

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


Reflection4

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 Application


Diffuse reflection

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.


When you stand 2 meters in front of a plane mirror your image is1

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.


Refraction

Refraction

Refraction

  • bending of light when it passes from one medium to another

  • caused by change in speed of light


Refraction1

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.


Refracted light that bends toward the normal is light that has1

Refraction

CHECK YOUR ANSWER

Refracted light that bends toward the normal is light that has

A.slowed down.

  • sped up.

  • nearly been absorbed.

  • diffracted.


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.


Refracted light that bends away from the normal is light that has1

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.


Refraction2

Refraction

Illusions caused by refraction

  • Objects submerged in water appear closer to the surface.


Refraction3

Refraction

Illusions caused by refraction (continued)

  • Objects such as the Sun seen through air are displaced because of atmospheric refraction.


Refraction4

Refraction

Illusions caused by refraction (continued)

  • Atmospheric refraction is the cause of mirages.


Which of these would not exist if light didn t slow in transparent materials

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.


Which of these would not exist if light didn t slow in transparent materials1

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.


Color

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.


Color1

Color

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.


Color2

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


Color3

Color

Additive primary colors (red, blue, green):

red + blue = magenta

red + green = yellow

blue + green = cyan


Color4

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

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.


When white light passes through a prism green light is bent more than1

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


Dispersion1

Dispersion

Rainbows

  • a colorful example of dispersion


Dispersion2

Dispersion

Rainbow detail


Dispersion3

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)


Dispersion4

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.


Compared with the primary rainbow the secondary bow1

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.


Polarization

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.


Polarization1

Polarization

Unpolarized light

  • vibrations producing light are in random directions


Polarization2

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.


Polarization3

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

Polarization

CHECK YOUR NEIGHBOR

Polarization occurs for waves that are

A.transverse.

  • longitudinal.

  • Both A and B.

  • Neither A nor B.


Polarization occurs for waves that are1

Polarization

CHECK YOUR ANSWER

Polarization occurs for waves that are

A.transverse.

  • longitudinal.

  • Both A and B.

  • Neither A nor B.


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