chapter 24 - particle physics

Question 1

plum pudding model

Answer 1

atom contained neg electrons embedded in a sea of uniform pos charge

Question 2

Rutherfords alpha scattering experiment

Answer 2

• fired a narrow beam of alpha particles with the same KE at at piece of thin gold foil - so particles are defelected once - one layer of atoms
• alpha was scattered by foil and detected on a screen - when they hit the screen produced a speck of light

Question 3

Rutherfords alpha scattering experiment observations/ conclusion

Answer 3

• most passed through with little scattering - mostly empty space
• very few were deflected - mass was mostly concentrated in a small area - of positive charge

Question 4

size of atom/ nucleus

Answer 4

the fraction of the particles scattered a lot = the fraction of the atom taken up by the nucleus
nucleus radius = 10^-14
atom radius = 10^-10m
1mm dot on a 100m running track

Question 5

how is radius of atom estimated

Answer 5

use distance of closest approach - fire alpha particle directly at it
KE > EPE - where it stops
1/2mv^2 = kQq/r^2
solve for r

Question 6

neutrons discovered

Answer 6

Chadiwck noticed that alpha particles hitting beryllium nuclei knock off neutrons

Question 7

nuclear model of atom

Answer 7

nucleus contains positive protons and uncharged neutrons
proton and neutron have about the same mass

Question 8

isotopes

Answer 8

same number of protons with different number of neutrons
isotopes of same element undergo same reactions

Question 9

atomic mass unit

Answer 9

one atomic mass unit is 1/12 the mass of a neutral C-12 atom

Question 10

nuclear size

Answer 10

radius depends on nucleon number (A)
R = r0A^1/3
where r0 = 1.2fm (10^-15) - radius of a hydrogen nucleus (one proton)

Question 11

strong nuclear force

Answer 11

acts between all nucleons
short range force (effective over a few fentometres)
attractive to 3fm
and repulsive below 0.5fm
large - much more than electrostatic

Question 12

antimatter

Answer 12

every particle has a corresponding antiparticle
has same mass and opposite charge
if the two meet they destroy each other - annihilation - mass of poth particles are converted into a high energy pair of photons
symbol is bar over letter

Question 13

fundamental forces

Answer 13

weak nuclear force - responsible for beta decay
strong nuclear - experienced by nucleons
electromagnetic - experienced by static and moving charges
gravitional - experienced by masses

Question 14

weak nuclear force

Answer 14

responsible for beta decay within unstable nuclei

Question 15

fundamental particles

Answer 15

has no internal structure - cant be divided smaller
eg quarks, electrons, neutrinos (leptons)

Question 16

hadrons

Answer 16

affected by strong nuclear force
decay by weak nuclear force
if charged exoerience EM force
made up of quarks
heavy
eg protons, neutrons, mesons

Question 17

2 types of subatomic particle

Answer 17

hadrons
leptons

Question 18

leptons

Answer 18

not affected by strong nuckear force
if charged experience EM force
fundamental particels
light
eg electrons, neutrinos, muons
electron, muon tau charge -1
neutrinos charge 0
all lepton number 1

Question 19

quarks

Answer 19

make up hadrons - fundamental particle
6 quarks with antiquarks
up, down
charm, strange
top, bottom

Question 20

up quark

Answer 20

charge + 2/3
baryon +1/3
lepton 0

Question 21

down quark

Answer 21

charge -1/3
baryon +1/3
lepton 0

Question 22

strange quark

Answer 22

charge -1/3
baryon +1/3
lepton 0

Question 23

antiquarks

Answer 23

same mag of charge/ baryon but opposite sign

Question 24

class of quarks

Answer 24

up, down
charm, strange
top, bottom
2/3, -1/3 charge
1/3, 1/3 baryon
increase in mass/ energy as you go down

Question 25

protons

Answer 25

+1 charge
uud

Question 26

neutrons

Answer 26

neutral charge
udd

Question 27

2 types of hadrons

Answer 27

mesons
baryons

Question 28

baryons

Answer 28

• all hadrons with 3 quarks
  eg proton, neutrons

Question 29

mesons

Answer 29

• hadrons made of a quark and antiquark
  eg pion, kaon

Question 30

neutrino

Answer 30

no charge - tiny mass
leptons
3 types - electron, muon and tau
each also has its own antineutrino

Question 31

beta decay

Answer 31

due to weak nuclear force
either beta - or beta +

Question 32

beta - decay

Answer 32

neutron changes to proton and electron
neutron > proton + electron + anti electron neutrino
d > u + e- + anti electron neutrino

Question 33

beta + decay

Answer 33

proton changes to a neutron and positron
proton > neutron + positron + electron neutrino
u > d + e+1 + electron neutrino

Question 34

conservation

Answer 34

in particle interactions have to conserve:
- charge
- baryon number
- lepton number
- stangeness (-1 strange, 0 for every other quark)