properties of light and spectrophotometry a.p. biology mr. knowles spectrophotometry
TRANSCRIPT
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Properties of Light and Spectrophotometry
A.P. Biology
Mr. Knowles
Spectrophotometry
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What is light?
Light is visible energy!
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Some animals can see other parts of the EM spectrum!
Who can “see” IR?
The Story of Pit Vipers!
Video: Discovery- Viper
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Am
pli tu
de
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How does wavelength compare to energy?
An Application: Video- The Blue Planet: The Deep
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Relationship Between Wavelength and Energy
• Wavelength and Energy Level are inversely related.
• The shorter wavelength, higher energy level.
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Light and Wavelength • Length of a light ray- wavelength.
• Usually represented by the Greek letter lambda ().
• Sun produces a continuous spectrum of EM radiation.
• Visible light is from about = 420 nm (blue) to 680 nm (red).
• Ultraviolet Light is = 100-400 nm.
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What happens when light strikes an object (molecule)?
• Reflection
• Refraction
• Transmission
• Absorption
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Absorption
• Absorption- when light rays do not pass through nor do they bounce back, but are used; when light rays are neither transmitted nor reflected, they are absorbed.
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How do molecules absorb light?
• Molecules have various chemical bonds with electrons in certain energy states.
• Some of these electrons become excited by the light energy and absorb it.
• Because of the electron’s specific energy state, these electrons can only absorb certain wavelengths.
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What determines absorbance of a molecule?
• Chemical nature – bond type, atomic structure of molecule.
• Concentration of Molecule – how much is present.
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Absorbance is a Molecular Fingerprint!
• Every molecule has its own unique absorption spectrum – ability to absorb certain wavelengths (energy) better than others.
• Can be used to identify molecules.
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Abs. Max of b = 453 nm
Abs. Max of a = 430 nm
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Eyes are not created equal!
The Story of the Amazing Owl Eye!
Video: Built for the Kill-Night
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What would happen if an eye had more cone cells? All the better to see your
color, my dear!
Video: Discovery- How They Hunt (Mantis Shrimp Eye)
Or
Discovery- Extreme Senses
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What happens to the energy of absorbed light?
• Energy from light rays can be used.
–Green leaf absorbs all wavelengths (except green) for use in photosynthesis.
• Energy from absorbed light is transformed into heat.
–Ex. Black car on a hot day.
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Transmission
• Transmission- passage of light through an object.
• Opaque objects cannot transmit any light.
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How do molecules transmit light?
• Wavelengths of light that cannot be absorbed are transmitted through the molecules with no change.
• Absorption and Transmission are inversely related.
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What happens to the energy of absorbed light?
• Absorbed light rays are changed into longer wavelengths and reemitted- luminescence
• Bacteria and other organisms can bioluminesce
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Reflection
• Reflection- particular wavelengths strike an object and bounce back
• Reflected wavelengths give objects color.
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Refraction• Refraction- bending of light as it
passes from one medium to another of a different density.
• Index of Refraction- a measure of the speed at which light passes through a material.
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