Chapter 6 - Interactions Between Light and Matter Flashcards
what is light? definition and composition/structure
ELECTROMAGNETIC RADIATION, oscillating electric and magnetic fields
in vacuum travels at the speed of light (surprise), 3 x 10^8 m/s
generally composed of electric field component and magnetic field component, same direction but perpendicular to each other. Same wavelength
speed of light
3 x 10^8 m/s OR more precisely 2.998 x 10^8
what proved that light behaves as a wave?
1801 observed that light undergoes diffraction and interference when travelling through small slits
equation relating wavelength frequency and speed of electromagnetic wave
c = frequency (italic v) * wavelength
c is speed of light
equation relating wavelength frequency and speed of electromagnetic wave
c = frequency (italic v) * wavelength
c is speed of light
*same equation as velocity = wavelength * frequency
monochromatic waves
light consisting only of waves with the same wavelength
coherent light & example
light w/ same wavelength AND produced at the same time ex laser
incoherent light
different wavelengths and/or produced at different moments of time ex. a lightbulb
so light can be monochromatic and incoherent (same wavelength but prod at different times, or monochromatic and coherent)
linearly polarized light
waves with electric and magnetic field components vibrating on the same plane (also plane waves)
formed passing unpolarized light through polarizer which only allows light with waves in a certain orientation through
should you assume light is polarized?
NO, unpolarized
what range of wavelengths can our eyes detect?
visible light, 390 to 760 nm
approx wavelength/frequency range radio waves (dont necessarily need to memorize)
frequency approx 10^4 - 10^10 s^(-1)
wavelength approx 10^4 - 10^-2 m
approx wavelength/frequency range microwaves (dont necessarily need to memorize)
frequency approx 10^9 - 10^11 s^(-1)
wavelength approx 10^1 - 10^-3 m
approx wavelength/frequency range infrared (dont necessarily need to memorize)
frequency approx 10^11 - 10^15 s^(-1)
wavelength approx 10^-3 - 10^-6 m
approx wavelength/frequency range ultraviolet (dont necessarily need to memorize)
frequency approx 10^15 - 10^17 s^(-1)
wavelength approx 10^-6 - 10^-9 m
approx wavelength/frequency range xrays (dont necessarily need to memorize)
frequency approx 10^17 - 10^21 s^(-1)
wavelength approx 10^-9 - 10^-13 m
approx wavelength/frequency range gamma rays (dont necessarily need to memorize)
frequency approx 10^19 - 10^24 s^(-1)
wavelength approx 10^4-11- 10^-16 m
different types of light organized from lowest frequency and largest wavelength to highest f and lowest wavelength
radio, microwave, infrared, visible, ultraviolet, x-rays, gamma rays
range of visible light (different colours from low f ^ wavelength to ^ f low wavelength)
black, red, orange, yellow, green, blue, indigo, violet (just a rainbow)
how does light passing through a prism work?
incident light is dispersed by refraction, the angle light exits at depends on it’s original wavelength. light diff wavelengths is seperated so we see variation in colour
what proves that light has particle like properties?
light acts as a particle when colliding with electrons - deflects, and wavelength changes
photon
particles of light, like little packages of energy and momentum
carries energy proportional to radiation frequency but has zero rest mass
equation for energy of a photon
E = pc = hc/wavelength = hv
where v is frequency, h is planck’s constant, p is momentum, c is the speed of light
most important part - E = planck’s * frequency
planck’s constant (actual #)
6.626 x 10^(-34)
how many particles in a mole?
6.022 x 10^23
if you’re given frequency wavelength etc and asked to calculate energy in joules/mole, what do you do?
use E = pc = hc/wavelength = hv, which is energy for a single photon then multiply by 6.022 x 10^23
what determines the brightness/intensity of light acc. to wave interpretation of light
the amplitude of waves, ^ amplitude = brighter/more intense
what determines the brightness/intensity of light acc. to particle interpretation of light
the density of photos, ^ photon density = brighter
if asked to draw, diagram w two beams of light, each dot represents a photon w/ same energy and momentum just draw denser for brighter light
what is a watt (W)
1 J/s
how to convert mW into joules
divide by 1000
photoelectric effect
phenomenon where electrically charged particles are ejected from a solid substance when it is struck with electromagnetic radiation (light)
explanation - photoelectric effect and frequency
a material can only be ionized by light of a certain energy (determined by the frequency of the light, E = hv)
before the minimum frequency (threshold frequency) no electrons are ejected no matter what, but after that frequency the kinetic energy of the electrons ejected increases proportionate to the frequency of the incident light
- slope of the line comparing frequency of light and energy of ejected electrons is planck’s constant
relationship between energy of light, binding energy, kinetic energy of electrons
E light = E binding + E kinetic
KE of ejected electron originates from energy of the incident light, some energy consumed by removing the electron from the surface (E binding)
relationship between the intensity of light and electrons emitted
E light is the energy of a photon, so if light is more intense (more dense), more photons therefore more electrons emit from the surface
summary of photoelectric effect process
photon strikes a surface with energy greater than binding energy, and electron can be emit. the energy of this electron is equal to the energy of the light striking the surface - binding energy which is determined by the electrostatic attraction between electron and nuclei. the number of electrons ejected is proportional to # of photons which strike the surface of the material (intensity of incident light)
how to spectrums inform us about quantum states
gives info about transitions between states because the energy diff between states equals the energy of the photons emitted or absorbed
absorption spectrum
a spectrum obtained by irradiating (i guess just striking) a sample with electromagnetic radiation and measuring the amount of light absorbed at each spec wavelength, if light absorbed a single line at the wavelength of absorption is observed
emission spectrum
obtained by exciting sample to higher energy quantum state by treating with an energy source (heat, electrical discharge, high energy light) measuring specific wavelengths emit as sample relaxes, same as absorption if light emit at particular wavelength a signal line will appear at this wavelength
why are there dark lines on a spectrum of visible light from the sun
some light at certain frequencies is absorbed by chemical species in the outer regions of the sun (hydrogen, sodium, magnesium)
relationship energy and wavelength
higher energy, lower wavelength
atomic spectroscopy
determining elemental composition by electromagnetic spectrum
measure energy of light absorbed or emit by atoms/ions when changing electronic quantum states
equation for difference in energy between two energy levels (n values)
change in energy = e final - e initial = -2.18 x 10^(-18) * Z^2 * (1/nfinal^2 - 1/ninitial^2)
z is atomic number, # protons in atom (atomic identity), at the top of the element symbol on the periodic table
hydrogen’s z is 1 which is why it looks like its not included when the equation is applied to hydrogen
how do you find wavelength of light with change in n value
use the equation change in e = -2.18 x 10^(-18) * Z^2 * (1/nfinal^2 - 1/ninitial^2) to calculate the energy absorbed or emit, then convert that to wavelength or frequency using the relationship E = h*frequency(which is italic v) = hc/wavelength
how many joules in a kilojoule
1000
what is the product of frequency and wavelength of light, is it a constant
product is velocity, and speed of light is a constant (c)
thing to pay attention to when calculating energy
is it asking per particle or per mole???
