energy levels and photon emission

Question 1

how do electrons in atoms exist

Answer 1

in discrete energy levels. electrons in an atom can only exist in certain well defined energy levels

Question 2

what is each level given

Answer 2

a number, with n = 1 representing ground state

Question 3

how can electrons move down energy levels

Answer 3

by emitting a photon

Question 4

what can the value of each photon be

Answer 4

these transitions are between definite energy levels so the value can only take a certain allowed value

Question 5

why is the joule not used

Answer 5

the values are so tiny it makes sense to use eV

Question 6

what is an electron volt defined as

Answer 6

the kinetic energy carried by an electron after it has been accelerated through a potential difference of 1 volt

Question 7

what does 1eV equal

Answer 7

1.60 x 10^-19 J

Question 8

what is the energy carried by each photon equal to

Answer 8

the difference in energies between the two levels

Question 9

show an equation representing transition from a higher energy to a lower energy

Answer 9

E(delta) = E2 - E1 = hf = hc/lambda

Question 10

how can electrons move up energy levels

Answer 10

absorbing a photon with the exact energy difference between the two levels

Question 11

what is the movement of an electron to a higher energy level called

Answer 11

excitation

Question 12

what if an electron is removed from the atom

Answer 12

we say the atom is ionised

Question 13

what is the ionisation energy of an atom

Answer 13

the amount of energy needed to completely remove an electron from the atom from the ground state, n = 1

Question 14

how do fluorescent tubes produce light

Answer 14

they use excited electrons

Question 15

what do fluorescent tubes contain

Answer 15

mercury vapor, across which an initial voltage is applied

Question 16

what does the high voltage do

Answer 16

accelerates fast moving free electrons that ionise some of the mercury atoms, producing more free electrons

Question 17

what happens when the flow of mercury atoms collides with electrons in other mercury atoms

Answer 17

the electrons in the mercury atoms are excited to higher energy levels

Question 18

what happens next

Answer 18

when these electrons return to their ground state, they emit photons in the UV range

Question 19

what absorbs these photons

Answer 19

a phosphor coating on the inside of the tube absorbs these photons, exciting its electrons to much higher orbits.

Question 20

what happens next

Answer 20

these electrons cascade down to the energy levels emitting many lower energy photons in the form of visible light

Question 21

what do fluorescent tubes also produce

Answer 21

line emission spectra

Question 22

how do you get a line spectrum

Answer 22

if you split light from a fluorescent tube with a prism or a diffraction grating you get a line spectrum

Question 23

what is a line spectrum seen as

Answer 23

a series of bright lines against a black background

Question 24

what does each line correspond to

Answer 24

a particular wavelength of light emitted by the source

Question 25

what wavelengths can you see

Answer 25

since only certain photon energies are allowed you can only see wavelengths corresponding to these energies

Question 26

what does shining a white light through a cool gas give

Answer 26

an absorption spectrum

Question 27

what does a continuous spectra contain

Answer 27

all possible wavelengths

Question 28

what is the spectrum of white light

Answer 28

continuous

Question 29

what happens if you split the light up with a prism

Answer 29

the colours will merge into each other with no gaps in the spectrum

Question 30

what emits a continuous spectrum

Answer 30

hot things emit a continuous spectrum in the visible and infrared

Question 31

why are all wavelengths allowed

Answer 31

because electrons are not confined to to energy levels in the object. the electrons are not bound by atoms and are free

Question 32

what do cool gases do

Answer 32

remove certain wavelengths from a continuous spectrum

Question 33

what do you get when light with a continuous spectrum of energy passes through a cool gas

Answer 33

line absorption spectrum

Question 34

where will most of the electrons in a gas atom be in low temperatures

Answer 34

ground states

Question 35

what can these electrons absorb

Answer 35

only photons with energy equal to the difference between two energy levels

Question 36

what happens to the photons

Answer 36

photons of the corresponding wavelengths are absorbed by the electrons to excite them to higher energy levels