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# Chapter 27 - PowerPoint PPT Presentation

Chapter 27. Properties of Light. Electromagnetic Radiation. Light. Photons. Diffraction. Diffraction is the slight bending of light as it passes around the edge of an object. The amount of bending depends on the relative size of the wavelength of light to the size of the opening.

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### Chapter 27

Properties of Light

Light

Photons

• Diffraction is the slight bending of light as it passes around the edge of an object. The amount of bending depends on the relative size of the wavelength of light to the size of the opening.

Regardless of the angle at which the wavefronts approach the barrier, one general law of reflection holds true: the waves will always reflect in such a way that the angle at which they approach the barrier equals the angle at which they reflect off the barrier.

• Light

• pure energy

• Electromagnetic Waves

• energy-carrying waves emitted by vibrating electrons

• Photons

• particles of light

• The speed of light is the same for all seven forms of light.

• It is 300,000,000 meters per second or 186,000 miles per second.

• German American physicist A.A. Michelson

• Using this method, Michelson was able to calculate c = 299,792 km/s

Picture credit

• A range of light waves extending in wavelength from radio waves to gamma rays

• Microwaves - used to cook

• Infrared - “heat waves”

• Visible Light - detected by your eyes

• Ultraviolet - causes sunburns

• X-rays - penetrates tissue

• Gamma Rays - most energetic

A range of light waves extending in wavelength from about 400 to 700 namometers.

• Is it correct to say that radio wave is a low-frequency light wave?

• Is a radio wave also a sound wave?

• See question on page 455.

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• Transparent - the term applied to materials through which light can pass in straight lines

• The following are transparent materials, which does light travel through fastest?

• Water at 0.75c

• Glass at 0.67c

• Diamonds at 0.40c

• Opaque - the term applied to materials that absorb light

• Are clouds transparent or opaque to visible light?

• Are clouds transparent or opaque to ultraviolet light?

• Why do metal objects reflect light back?

• The electrons are loose in metals (remember conductors) and do not spring energy from atom to atom. Rather they remit visible light

• Umbra - the darker part of a shadow where all the light is blocked

• Penumbra - a partial shadow

• These terms also apply to Solar Eclipses and Lunar Eclipses.

Umbra

Sun

Earth

Moon

Penumbra

• A solar eclipse occurs when the Moon passes in front of the Sun.

Sun

Earth

Moon

• A lunar eclipse occurs when the Moon passes into the Earth's shadow.

up and down – say it is

linearly polarized.

Light can have other types of polarizations such as circularly polarized

or elliptically polarized. We will only look at linearly polarized light.

Polarization

Net electric field is zero – Unpolarized light!

chained molecules which absorb

light with electric fields

perpendicular to the axis.

How do we make Polarized Light?

I. Polarizers-

Questions Polarization axis and another object with a horizontal polarization axis are placed next to each other.

• Which type of eclipse is dangerous to view with the unprotected eye?

• Why are lunar eclipses more commonly seen than solar eclipses?

• See question on page 460.

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### Chapter 27 Review Questions Polarization axis and another object with a horizontal polarization axis are placed next to each other.

You will observe a total eclipse of the sun when... Polarization axis and another object with a horizontal polarization axis are placed next to each other.

(a) you stand in the penumbra of the moon’s shadow

(b) you stand in the umbra of the moon’s shadow

(c) sunlight diffracts around the moon

(d) sunlight reflects from the moon to the earth

(b) you stand in the umbra of the moon’s shadow

The speed of light... Polarization axis and another object with a horizontal polarization axis are placed next to each other.

(a) has never been measured

(b) is about the same as that of sound

(c) is infinitely fast

(d) is very fast, but not infinite

(d) is very fast, but not infinite

In the dark at late evening, no color is seen because of lack of stimulation of

a. rods.

b. cones.

c. cornea.

d. crystalline lens.

b. cones.

End of Chapter 25 lack of stimulation of