SEC 4 6 LIGHT AND MATTER LIGHT Light
- Slides: 26
SEC. 4. 6 - LIGHT AND MATTER
LIGHT • Light- a form of electromagnetic radiation • Electromagnetic radiation- energy in wave form that has electric and magnetic fields • Every wave of electromagnetic radiation travels at the speed of light • There is a huge range of different types of electromagnetic radiation- only a very small portion of all radiation is visible!
ELECTROMAGNETIC SPECTRUM
WAVE PROPERTIES • Waves have several defining properties- crest, trough, frequency and wavelength • Crest- highest point on wave • Trough- Lowest point on wave
• Frequency- measures the number of times a wave completes a cycle in one second (cycles per second are “Hertz”, shortened as “Hz”) • High frequency: • Low frequency:
• Wavelength- the length between two adjacent crests or two adjacent troughs- measured in meters • Large wavelength: • Small Wavelength:
• When a wave has a high frequency, what is true about it’s wavelength? Look back at your wave diagrams • When a wave has a low frequency, what is true about it’s wavelength? • From this, how are wavelength and frequency related?
• The frequency of a wave, as well as the wavelength is related to the energy that wave has • When a wave has a high frequency, it has a high amount of energy, and vice versa
• When a wave has a large wavelength, it will have a small amount of energy, and vice versa • For a wave with high energy, it will have a high frequency, and a low wavelength
VISIBLE RANGE • Visible light has a fairly small range in wavelengths 400 nm-700 nm • Different wavelength values correspond with different colors…which means different colors correspond with different amounts of energy 400 nm 700 nm Visible light
• Which color of light has the highest energy? • Which color of light has the lowest amount of energy? • ROYGBIV
PHOTONS- QUANTIZED • Electromagnetic radiation travels in “packets” called photons • Photon= light packet • Must have full photons- cannot have fractions of photons • Radiation is said to be “quantized” because of this- it comes in certain amounts of photons
LIGHT INTERACTION WITH MATTER • Ground State- most stable electron configurationelectrons occupy the lowest energy levels they possibly can • When photons of light run into atoms, the electrons in the atom can absorb the photon
• When electrons absorb photons, they are able to “hop” to higher energy levels- being further away from the nucleus requires more energy • Excited state- when electrons jump to higher energy levels
• The difference between the ground state and the excited state will be equal to the energy of the photon • The process of electrons absorbing photons and jumping to higher energy levels is known as excitation • Excited state- higher energy, but not very stable
• Electrons will not remain in an excited state for longthey will want to return to ground state • When electrons return to ground state, they must release energy • When electrons release energy, they release it as a photon
• How much energy will this released photon have? • Relaxation- process of an excited electron releasing energy and returning to ground state
DRAWING EXCITATION AND RELAXATION
RELEASED ENERGY IS UNIQUE • Every element has a unique set of energy levels • Due to these unique sets of energy levels, each element will absorb/release different (and unique) amounts of energy
• Since energy is related to the frequency and wavelength of light- different elements absorb/release different (unique) wavelengths/frequencies of light • Different wavelength of light= different color
• This is why fireworks explode in different colors- the fireworks have different types of elements in them- causing different colors of light to release • In a way- the color of light a substance releases is a fingerprint- we can use it to identify unknown substances
• Flame test- by knowing the color of a flame, we can find the amount of energy that excited electrons are releasing- based on that specific energy, we can identify the substance
WAYS OF PRODUCING LIGHT • Fluoresence- when something absorbs light, and releases light immediately afterward- relaxation happens quickly • Phosphorescence- light is absorbed, then released over a period of time- relaxation occurs slowly • Incandescence- when something is heated (electrons are gaining energy from heat, not photons), then releases light during relaxation
• Chemiluminescence- electrons absorb energy from a chemical reaction to cause excitation, then relaxation produces visible light • Bioluminescence- electrons absorb energy from a chemical reaction that occurs in a biological organism, then relaxation produces visible light • Triboluminesence- when pressure is applied to a crystal to excite electrons, then release light (typically when the crystal shatters)
• Which form of light production would be responsible for the following examples: • Glowing Algae: • Mixing liquids from glow sticks: • Glow in the dark stars/t-shirt:
• Light bulb: • Tonic water under UV light: • Wint-o-green Lifesaver sparking when you chomp on it:
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