2.5 Quantum Physics

Question 1

photons

Answer 1

discrete energy quanta

Question 2

what is energy of photon directly proportional to

Answer 2

frequency of EM radiation

Question 3

equation linking energy of photon and frequency

Answer 3

E=hf

Question 4

1 electronvolt

Answer 4

energy transferred when an atom travels through a potential difference of 1 volt

Question 5

photoelectric equation

Answer 5

1/2mv2 = hf - hf0

Question 6

what happens if the frequency is above the threshold frequency

Answer 6

increased intensity radiation increases rate of electron emission

Question 7

photoelectric effect

Answer 7

EM radiation above threshold frequency shone into metal, electrons are released from surface of metal

Question 8

how is photoelectric effect demonstrated

Answer 8

gold leaf electroscope

Question 9

what happens when visible light is used on the zinc plate?

Answer 9

no electrons removed from plate

Question 10

what happens when UV light is used on the zinc plate?

Answer 10

very low intensity - electrons instantaneously removed from plate

Question 11

work function

Answer 11

minimum energy required to free an electron from the surface of the metal

Question 12

threshold frequency

Answer 12

minimum frequency required to free electrons from surface of metal

Question 13

ground state

Answer 13

lowest energy level for electron in atom

Question 14

excited state

Answer 14

electrons gain energy and can move to higher energy level

Question 15

ionisation state

Answer 15

electrons gain enough energy to completely remove from atom

Question 16

how can electrons gain energy needs

Answer 16

absorbing photon of light

Question 17

energy levels

Answer 17

different values, each of possible electron transitions within atom will produce photon with different energy

Question 18

what would happen f the electron gained enough energy to make it all the way to 0eV?

Answer 18

electron free of hydrogen atom
atom missing electron
becomes hydrogen ion

Question 19

use of lasers

Answer 19

interference experiments in labs which require coherent source of light
endoscopes for microsurgery - lasers are precision instruments
CD readers and writers - lasers retrieve data by reflecting off microscopic pits on discs

Question 20

lasers acronym

Answer 20

light amplification by stimulated emission of radiation

Question 21

what is a laser

Answer 21

device that controls the way that energised atoms release photons

Question 22

population inversion

Answer 22

number of electrons in excited state more than number in ground state

Question 23

how does population inversion occur?

Answer 23

very intense flashes of light/electric discharges pump lasing medium and create large collection of excited-state

Question 24

properties of laser light

Answer 24

monochromatic
coherent
collimated - very tight beam and very strong & concentration

Question 25

what occurs to make the 3 properties of laser light happen?

Answer 25

stimulated emission

Question 26

production of x-rays in x-ray machine

Answer 26

electrode pair sit inside glass vacuum tube cathode = heated filament heat causes electrons to be ejected off filament surface positive charged anode flat disc of tungsten attracts electrons across tube causing them to accelerate electrons hit tungsten target and give off most energy - most as heat speeding electrons collides with tungsten atom, knocks loose electron in one of atom's lower energy levels electrons in higher energy level immediately falls to lower energy level, releasing extra energy in form of x-ray photon

Question 27

CT scanning advantages

Answer 27

provides real time lagging painless, non-invasive and accurate fast and simple less sensitive to patient movement that MRI performed if have implanted medical device of any kind e.g. pacemaker

Question 28

CT scanning disadvantages

Answer 28

more expensive that conventional X-ray x-ray dose higher than conventional x-ray person large may not fit into opening of scanner/too heavy for table not recommended for pregnant women children more sensitive to ionising radiation - shouldn't have CT scan unless necessary

Question 29

How does CT scanner work?

Answer 29

x-ray tube mounted on movable ring around edges of hole rings supports x-ray detectors directly opposite x-ray tube motor moves rings so x-ray tube and detectors revolve around body x-ray beams moves all around patient scanning from 100s of different angles each full revolution scans narrow, horizontal 'slice' of body computer takes all info and creates 3D image of body