Energy Levels And Photo Emission Flashcards
Each level is given a number. What number represents the ground state
N=1
What do electrons in an atom exist in
Discrete/well-defined energy levels
Electrons can move …. An energy level by emitting a ….
Down
Photon
Why can the energy of each photon emitted only take a certain allowed value
Since the TRANSITIONS are between DEFINITE ENERGY LEVELS
What do we use instead of the unit joules and why
ELECTRONVOLT (eV)
The ENERGIES involved are so TINY
What is the definition of an ELECTRONVOLT (eV)
The KINETIC ENERGY carried by an electron
After it has been ACCELERATED through a PD of 1 volt
What does the energy gained by an electron (eV) equal
That accelerating voltage (V)
What does 1 eV equal in joules
1.6*10-19
What is the energy carried by each photon equal to
The difference in energies between two levels
Should you be concerned that the energy is negative
No. Don’t worry about it
Write down the equation for a transition between two energy levels
E=e1-e2=hf=hc/y
What do fluorescent tubes use to produce light
Excited electrons
What does fluorescent tubes contain
MERCURY VAPOUR
Across which a HIGH VOLTAGE is applied
What happens caused by the high voltage being applied to the mercury vapour
The ELECTRONS in the MERCURY
COLLIDE
With the FAST-MOVING FREE ELECTRONS (accelerated by the HIGH VOLTAGE)
They’re EXCITED to a higher ENERGY LEVEL
After the electrons are excited to a higher energy level, what happens to them
When they return to their GROUND STATE
They emit PHOTONS in the UV range
What costing is on the inside of the fluorescent tube
Phosphorus
What does the phosphorus coating on the inside of the tube do
ABSORB the PHOTONS
EXCITING it’s ELECTRONS to much higher ORBITS
ELECTRONS then CASADE down the ENERGY LEVELS
EMITTING many LOWER ENERGY PHOTONS
In the form of VISIBLE LIGHT
Fluorescent tubes product what (in terms of spectra)
Line emission spectra
What are the two ways you could split tight from a fluorescent tube
Prism
Diffraction grating
If you split the light from a fluorescent tube with a prison or a diffraction grating what do you get
Line spectrum
What is a line spectrum seen as
SERIES of
BRIGHT LINES against a
BLACK BACKGROUND
What does each LINE correspond with
A PARTICULAR WAVELENGTH of light EMITTED by the source
Why are their only certain corresponding wavelengths
Since only CERTAIN PHOTON ENERGIES are ALLOWED
What does shining white might through a cool gas give (in terms of spectrum)
ABSORPTION SPECTRUM
What does the continuous spectra contain
All POSSIBLE wavelengths
State a spectrum which is continuous
White light
What happens if you split white light up with a PRISM
COLOURS all MERGE into each other
There are NO GAPS
Other that white light, what also emits a continuous spectrum and in what
HOT THINGS in the VISIBLE and INFRARED
What does cool gases do to a continuous spectrum
REMOVE CERTAIN WAVELENGTHS
You get a ….. ….. ….. When light with a ….. ….. Of …. (…. ….) passes through cool gas
LINE ABSORPTION SPECTRUM
CONTINUOUS SPECTRUM
ENERGY
WHITE LIGHT
Explain why we get a line absorption spectrum when we shine white light through a cool gas
At low temp, most ELECTRONS in the gas atoms will be in their GROUND STATE
PHOTONS of the CORRECT wavelength are ABSORBED by the electrons to excite them to higher energy levels
What then happens to the photons of the correct wavelength absorbed by the electrons in the gas atoms
MISSING from the CONTINUOUS SPECTRUM when it comes out the other side of the gas
What do the black lines in the continuous spectrum correspond to
the ABSORBED WAVELENGTH
What would you expect if you compared the absorption and emission spectra of a particular gas
The black lines in the absorption spectrum match up with the bright lines in the emission spectrum
