Module 5 Cosmology Flashcards
What makes the line spectrum of elements different?
electron energy levels different for each chemical element
Define an energy level
the discrete energy with which electrons orbit the nucleus
Why are electron levels considered negative?
Energy is required to remove an electron from the atom
What is ionisation energy?
minimum energy required to remove electron that is closest to the nucleus (ground state)
What is the ground level?
n=1, first energy level in an atom (the most negative one)
What is excitation?
The process by which an electron moves from a lower to a higher energy level (by absorbing a photon)
Describe the process of excitation
Electron must receive the exact amount of energy
Usually by absorbing a photon
Electron gains this energy and moves to a higher energy level
What is de-excitation or relaxation?
the process by which an electron moves to a lower energy level by losing energy through emitting a photon
How do you find the number of possible wavelength that can be observed when firing a beam of electrons at a given KE at atoms using an energy level diagram?
Find the energy of electron in same units as energy diagram
Add this value to the value of the ground level (you should still get a negative number)
Take all the number of relaxations possible below this value (line below this value)
That is the number of wavelengths that can be observed ie the number of photons of different energies
What are the three main spectra?
Continuous
Emission line spectra
Absorption line spectra
What is continuous spectrum?
a spectrum containing all colours, wavelengths, and frequencies
How is a continuous spectrum produced?
viewing a white light through a diffraction grating
Describe an emission line spectrum?
a series of narrow, bright, coloured lines on a dark background
Explain how is an emission spectrum produced in terms of movement of electrons?
Each line is due to a photon of specific energy being emitted as electrons move to lower energy levels through relaxation
Gaps between levels have fixed energy therefor photons have fixed energy and wavelengths
Describe an absorption spectrum
A series of narrow dark lines on a continuous spectrum background
In simple terms, describe how an emission spectrum is produced
electron moves to a lower energy level by emitting a photon
How is an absorption spectrum produced?
When a continuous spectrum (from passing white light through a diffraction grating) passes through a cool gas
The gas absorbs certain photon energies producing excitation of electrons
Each photon absorbed (gap in spectra) corresponds to a gaps between energy levels
Producing a series of narrow dark bands on a continues background
How can an absorption line spectrum be used to identify elements
Each black line corresponds with a wavelength of photons being absorbed
Also corresponds to gaps between energy levels
Each element has a unique set of energy levels, thus can be compared to absorption spectrum
What is a diffraction grating?
Usually a piece of metal containing thousands of tiny slits of equal thickness which are equally spaced
State the diffraction grating equation
dsin0=nλ
Where are angles measured from when calculating diffraction gratings
from the central fringe (straight through position)
In the diffraction grating formula, what does d stand for?
distance between the gaps in the diffraction grating
When given a number of lines in a distance for a grating, how do you calculate d (use N=250 mm^-1)?
Take the unit of length over the number of divisions
1x10^-3/250
Explain how you calculate the largest number of orders that can be observed
Rearrange for n
sin90=1
n_max=d/λ
Truncate ie round down to nearest whole number