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Chapter 26. Properties of Light. Electromagnetic Waves. Recall… Light originates from the accelerated motion of electrons. Magnetic field…

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Chapter 26

Chapter 26

Properties of Light



Properties of light

  • Recall… Light originates from the accelerated motion of electrons.

  • Magnetic field…

  • The vibrating electric and magnetic fields regenerate each other to make up an electromagnetic wave, which emanates (moves outward) from the vibrating charge.


Electromagnetic wave velocity
Electromagnetic Wave Velocity

  • An electromagnetic wave traveling though space never changes its speed.

  • Electromagnetic induction and energy conservation keep light moving at the same speed.


Properties of light

  • IF light were to slow down, its changing electric field would generate a weaker magnetic field, which in turn, would generate a weaker electric field, and eventually the wave would die out.

  • No energy would be transported from one place to another

  • Therefore light cannot travel slower than it does.


Properties of light


Properties of light


James clerk maxwell
James Clerk Maxwell indefinitely, carrying energy forward without loss or gain.

  • He discovered that light is simply electromagnetic radiation within a particular frequency.

    • 4.3 x10^14 to 7 x10^14 vibrations per second

  • These waves activate the “electrical antennae” in the retina of the eye.

    • Lower frequencies appear red and higher frequencies appear violet.

  • Maxwell also realized that electromagnetic radiation of any frequency propagates at the same speed as light.


The electromagnetic spectrum
The Electromagnetic Spectrum indefinitely, carrying energy forward without loss or gain.

  • The classification of electromagnetic waves according to frequency.


Properties of light


Example
Example through space is identical to the frequency of the oscillating electric charge generating it.

  • Since the speed of the wave is 300,000 km/s, an electric charge oscillating once per second (1 hertz) will produce a wavelength of 300,000 kilometers.

    • This is because only one wavelength is generated in 1 second.

  • If the frequency were 1- hertz, then 10 wavelengths would be produced in 1 second.


Properties of light


Transparent materials
Transparent Materials only because we cannot see the montages of electromagnetic waves that permeate every part of our surroundings.


Properties of light


Properties of light


Properties of light

  • If a charged object is to respond to these ultrafast vibrations, it must have very little inertia, the electrons with the material must be so tiny that they can vibrate at this rate.

  • Such materials are referred to as transparent because they allow light to pass though it in straight lines


Properties of light

  • Glass is transparent to all frequencies of visible light. The frequency of the reemitted light.

  • The frequency of the remitted light that is passed from atom to atom is identical to the frequency of the light that produced the vibration in the first place.

  • Keep in mind that there is a light delay in between absorption and reemission.


Properties of light


Properties of light

  • Infrared waves, with frequencies lower than those of visible light, vibrate not only the electrons but the entire atoms or molecules in the structure of the glass.

  • This vibration increases the internal energy and temperature of the structure, which is why infrared waves are often called heat waves.


Opaque materials
Opaque Materials light, vibrate not only the electrons but the entire atoms or molecules in the structure of the glass.


Properties of light


Shadows
Shadows light without reemitting it.

  • A thin beam of light is often called a ray.

  • When we stand in the sunlight, some of the light is stopped while other rays continue in a straight-line path.

  • We cast a shadow – which is a region where light rays cannot reach.


Shadows cont
Shadows Cont. light without reemitting it.

  • A total shadow is called a umbra.

  • A partial shadow is called a penumbra, this appears where some of the light is blocked but where other light fills it in.


Seeing light the eye
Seeing Light – The Eye light without reemitting it.


Properties of light

  • Light enters the eye through the transparent cover called the cornea, which does about 70% of the necessary bending of the light before the light passes through the pupil.

  • The light then passes through the lends, which is used only to provide the extra bending power needed to focus images of nearby objects on the layer off the back of the eye.


Properties of light

  • The retina is not uniform. the cornea, which does about 70% of the necessary bending of the light before the light passes through the pupil.

  • There is a spot in the center of our field of view called the fovea, the region of most distinct vision.

  • Much greater detail can be seen here than at the side parts of the eye.

  • There is also a spot in the retina where the nerves carrying all the information exit along the optic nerve

    • This is the blind spot


Properties of light


Properties of light

  • The retina is composed of tiny antenna that resonate to the incoming light.

  • There are two kinds of antennae

    • The rods and the cones

  • There are three types of cones

    • Those that are stimulated by low-frequency light, those that are stimulated by intermediate frequencies of light and those that a stimulated to light of higher frequencies.

    • Color vision is possible because of the cones


Properties of light


Properties of light

  • The cones require more energy that the rods before they will “fire” an impulse through the nervous system.

    • We see low intensities with out rods

  • Rods and cones in the retina are not connected directly to the optic nerve.

  • While many of these cells are interconnected, only a few carry information to the optic nerve.


Properties of light

  • Through these interconnections, a certain amount of information is combined from several visual receptors and “digested” in the retina.

  • In this way the light signal is “thought about” before it goes to the optic nerve and then to the main body of the brain.

  • So some brain functioning occurs in the eye itself.

  • The eye does some of our “thinking” for us.


Properties of light
Iris information is combined from several visual receptors and “digested” in the retina.

  • The colored part of the eye that expands and contracts and regulates the size of the pupil, admitting more or less light as the intensity of light changes.

  • Ti so happens that the relative size of this enlargement or contraction is also related to our emotions.


Properties of light

  • The difference in light intensity may be more than a million to one.

  • Because of an effect called lateral inhibition, we don’t perceive the actual differences in brightness.

  • The brightest place s in out visual field are prevented from outshining the rest, for whenever a receptor cell on our retina sends a strong brightness signal to our brain, it also signals neighboring cells to dim their responses.

  • This allows us to discern detail in very bright areas and in dark areas as well