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 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- 400nm-700nm Different wavelength values correspond with different colors…which means different colors correspond with different amounts of energy Visible light 400 nm 700 nm
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 configuration- electrons 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 long- they 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: