Transcript But Light can Also Behave like a Particle

Light Can Act Like Waves or
Particles
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In 1801 Thomas Young an English scientist
did the Double slit experiment.
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Passed a beam of light through two narrow openings and
projected it onto a screen.
He found the light produced a striped pattern which
meant the light was constructively and destructively
interfering.
This meant that light is composed of waves.
But Light can Also Behave
like a Particle
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Other observations indicated that light can
also act like a particle:
– When light hits metal it knocks electrons off the
surface.
– They found that red light cannot knock electrons
off metal no matter how bright it is.
– If light were a wave then the brighter light
should have more energy.
– Photons are light particles that contain certain
amounts of energy based on their frequency and
wavelength.
– Blue light has a higher frequency and shorter
wavelength thus contains more energy than red light.
Relationship Between Frequency,
Wavelength and Energy
The Color of light is Determined By
its Frequency and Wavelength
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Red
Orange
Yellow
Green
Blue
Indigo
Violet
650
570
530
480
440
410
380
- 720 nm
- 650 nm
- 570 nm
- 530 nm
- 480 nm
- 440 nm
– 410 nm
The Perception of Color
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Our perception of blending colors is created by how our eyes
function.
– If a beam of red light and a beam of yellow light are shined
together we do NOT perceive orange light.
– Your eyes contain receptors called cones that are sensitive to red
, green , and blue light.
– These are known as the primary colors.
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If only the blue cones are stimulated then we will only
perceive blue light.
– If more than one type of cone is stimulated then we will
perceive a new color.
– These are known as secondary colors.
– If all three types of cones are stimulated we perceive white.
– If none of the cones are stimulated we don’t see any color or
perceive black.
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The frequency and wavelength of light
determine what color you will see.
– When you optical receptors perceive a wavelength of
550 nm you see green light.
– The colors that you see are a result of surfaces
reflecting various wavelengths of light back to your
eyes.
– White light
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When all of the primary colors are being reflected back to
your eyes.
– No light (or black)
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When all of the primary colors are being absorbed and no
light is being reflected back to your eyes.
The Brightness of Light
Depends on Intensity
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Intensity
– The quantity of light illuminating a
surface.
– Depends on the amount of light passing
through a certain area or space.
– Light spreads out in spherical wave
fronts.
– Light is more diffuse further from its
source.
Primary Pigments
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Pigments are substances that absorb
light.
The primary pigments are:
– Cyan Magenta Yellow
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These are also known as the
subtractive colors.
– Adding any of these two colors together
give you back the primary colors.
ROYGBIV
Human Eye Cone Sensitivities
Color Addition
• Reflected Red + Green = Yellow
• Reflected Blue + Green = Cyan
• Reflected Blue + Red = Magenta
Color Addition