Physics 130-3

Question 1

blackbody

Answer 1

a body that, when cool, would absorb all the radiation falling on it (and so would appear black under reflection when illuminated by other sources).

Question 2

as object’s temp increases, the wavelength of its peak intensity inc/dec

Answer 2

decreases

Question 3

quantum of energy

Answer 3

smallest amount of energy possible

Question 4

planck’s hypothesis

Answer 4

the energy of oscillating atoms, molecules, etc can only exist in discrete amounts that are multiples of the smallest amount of energy (the quantum of energy)

Question 5

photons

Answer 5

tiny particles of light

Question 6

true or false: each proton travels at the speed of light

Answer 6

true

Question 7

what are einstein’s 3 postulates about light quanta, related to photelectric effect?

Answer 7

1. Light of frequency f consists of discrete quanta, each of energy E=hf.
   Each photon travels at the speed of light c.
2. Light quanta are emitted or absorbed on an all-or-nothing basis. A substance can emit 1 or 2 or 3 quanta, but not 1.5. Similarly, an
   electron in a metal cannot absorb half a quantum but only an integer
   number.
3. A light quantum, when absorbed by a metal, delivers its entire energy
   to one electron.

Question 8

photoelectric effect

Answer 8

When light shines on a metal surface, electrons are found to be emitted from the surface.

Question 9

work function

Answer 9

minimum energy W0 from light that’s required just to get an electron out from metal. THIS IS NOT THE ENERGY PHOTOELECTRON HAS ONCE IT MOVES (THIS IS KE). work function is the energy it takes to simply remove electron from the metal so its no longer attracted the atoms in metal

Question 10

what does it mean if a monochromatic light beam has an increase of intensity?

Answer 10

intensity=energy/time/area. the energy of each photon is unchanged bc energy=hf and f isn’t changing. so increased intensity means there are more photons.

Question 11

cutoff frequency

Answer 11

minimum frequency of light that will supply enough energy to remove electron from metal. it’s the frequency when hf=work function.

Question 12

true or false: KE of electrons increases as f of photon does.

Answer 12

true. just look at
hf=KE+W. work function stays the same bc it’s a property of the metal

Question 13

electron volt

Answer 13

KINETIC energy acquired by a particle as a result of moving across a potential difference of 1 V. The particle’s charge = the magnitude of an electron charge

Question 14

true or false: For calculations, electron volts should be converted to joules using the conversion factor of 1 ev=1.6*10^-19 J

Answer 14

true. electorn volts is not an SI unit. if you’re looking for mass, velocity, etc of a particle based on its KE in electron volts, must convert KE to joules first

Question 15

what’s the difference between lyman and paschen series?

Answer 15

lyman finds wavelengths of UV light emitted by H atom, paschen finds wavelengths of IR light emitted by H atom

Question 16

how is wavelength of emitted light in line spectrum (excited gases emit light of only certain wavelengths) determined?

Answer 16

gas is made of atoms. electrons orbit the atoms at certain energy levels and when they fall back to ground state, they emit a photon with energy = Iinitial state-ground stateI. wavelegnth of photon is found by setting this energy =hc/lambda

Question 17

nucleons

Answer 17

a proton or neutron

Question 18

atomic number

Answer 18

number of protons in a nucleus. symbol is Z

Question 19

1. atomic mass number (aka mass number)
2. atomic mass
3. unified atomic mass unit

Answer 19

1. The total number of nucleons. symbol A
2. total mass of atom (mass of nucleons + mass of electrons)
3. a way to define mass of atoms. Symbol u. 1 u=1/12 of the mass of a carbon-12 isotope

Question 20

what is the amu of one nucleon

Answer 20

about 1 u. ___ nucleons = nuclear mass is ____ amu

Question 21

nucleon vs neutron

Answer 21

nucleon: a proton OR neutron
neutron: neutral charge in a nucleus. represented by N (=A - Z)

Question 22

true or false: a neutral atom always has the same number of protons and neutrons

Answer 22

false. it always has the same number of protons and ELECTRONS. Nuclei that contain the same number of protons but different numbers of neutrons are called isotopes.

Question 23

natural abundance

Answer 23

percent of each given isotope of an atom that naturally exists (for ex: almost 99% of natural existing carbon is in the isotope 12C)

Question 24

true or false: KE of alpha particle is always around 4-5 MeV

Answer 24

true

Question 25

why must the mass of a STABLE nucleus be less than the sum of the masses of its protons and neutrons?

Answer 25

because when protons and neutrons form the nucleus, this mass is lost as energy. This means the nucleus has a lower energy (and thus is more stable) than the protons/neutrons when they're separate.

Question 26

strong nuclear force

Answer 26

the force that binds all neutrons and protons together so they can form a nucleus

Question 27

radioactivity

Answer 27

the decay of an unstable nucleus. for atoms with an atomic number above 82, the repulsive force between protons overpowers the attractive nuclear force between protons/nucleons, leading to an unstable nucleus

Question 28

order radioactive ray from strongest to weakest: alpha, gamma, beta

Answer 28

1. gamma 2. beta 3. alpha

Question 29

parent and daughter nucleus

Answer 29

parent: original nucleus that decays and forms new nucleus (daughter) and alpha particle (He atom). DAUGHTER NUCLEUS ALWAYS HAS 2 LESS PROTONS AND 2 LESS NEUTRONS IN ALPHA DECAY

Question 30

disintegration energy (Q)

Answer 30

total energy released by decaying parent nucleus

Question 31

definition of activity of an isotope

Answer 31

the number of parent nuclei decaying per second

Question 32

half-life

Answer 32

the time it takes for half the nuclei in a sample to decay

Question 33

true or false: planck hypothesized energy of electrons must be discrete.

Answer 33

false. he hypothesized that in heated solids, the energy of oscillating atoms must be discrete. BOHR built on this an hypothesized energy of electrons orbiting atoms are too discrete.