Looking Inside The Atom

Question 1

Rutherford scattering experiment?

Answer 1

• alpha particle fired amd thin gold foil
• most went straight through so atom is mostly empty space
• some were deflected through large angles so centre must be positive to repel them
• very few scattered more than 90 degrees so nucleus must be tiny but more massive than the alpha particle
• most of mass must be in nucleus as fast particle still deflected

Question 2

How to calculate distance of closest approach?

Answer 2

-refelcts when epe is equal to ke so
Initial K.E=electrical potential energy=kq(alpha)Q(gold)/r
-r is distance of closest approach ie distance from nucleus

Question 3

How to find charge of nucleus

Answer 3

-proton has same charge as e
-So no of protons x charge of e
-

Question 4

What is the charge of an alpha particle?

Answer 4

+2e

Question 5

What is a hadron?

Answer 5

• Particles that have strong interactions
• reason protons and neutrons are held when they repel
• made up of quarks

Question 6

What are two hadrons and how do they differ?

Answer 6

• Proton a stable hadron
• neutron is a unstable hadrom that decays into a proton caused by the weak interaction when not in the nucleus
• reaction is n ~> proton + electrom +antineutrino
• neutrons not in the nucleus have a half life of 15 mins

Question 7

Whats a lepton

Answer 7

-Particle that interact via the weak interactions and gravity

Question 8

What 2 leptons od we need to know?

Answer 8

• electrons (-1 charge)

- neutrinos (0 charge 0 mass) symbol of v (but curvy), neutrinos only experience the weak interaction

Question 9

What is lepton number?

Answer 9

-number of leptons, electrosn and neutrinos is 1

Always conserved

Question 10

What is an antiparticle?

Answer 10

A corresponding particle w same mass but opposite charge

Question 11

What happens when energy is converted to mass

Answer 11

• equal amounts of matter and anti matter
• this is called pair production
• draw diagrams and check them in book

Question 12

When does pair production happen?

Answer 12

• when one photon has enough energy to produce that mass
• near a nucleus to ocnserve moentum
• usually get low mass particle
• calculate minimum energy using Erest=mc^2
• draw squiggly line into two curved lines of opposite particle

Question 13

What is annihilation?

Answer 13

• particle and antiparticle meet
• total mass converted to energy forming pair of identical photons
• use Ephoton=mc^2 to calculate the min energy of photons

Question 14

What are we assuming as negligible in annihilation?

Answer 14

Kinetic energy

Question 15

How long do amtiparticles exist for?

Answer 15

Fraction of a secomd so quickly anihilate after pai creation

Question 16

What are fundamental particles?

Answer 16

Quarks

Question 17

What quarks do we need to know?

Answer 17

• Up quark, symbol u, charge +2/3
• down quark,symbol d, charge -1/3
• also there anti quarks

Question 18

What quarks make a proton?

Answer 18

uud

=+2/3 +2/3 -1/3

Question 19

What quarks make a neutron?

Answer 19

udd

= +2/3 -1/3 -1/3

Question 20

What happens when u try sepertae quarks with lots of energy?

Answer 20

Energy transfeered to mass so pair production

Question 21

Each one of the 4 fundamental forces in nature has its own….

Answer 21

Gauge bosons (exchange particles when they interact)

Question 22

What is the gauge boson that causes the strong interaction and how does it cause pair creation?

Answer 22

Gluon
Causes strong foce in hadrons (protons and neutrons)
-when quarks in hadrons are pulled apart the energy in gluon field increases until a quark + anti quark pair is produced

Question 23

How does a linear particle accelerator work?

Answer 23

• long straight tube of electrodes
• connected to alternating pd supply so charge of electrode keeps changes from + to -
• timed so particles always attracted to the next electrode and reppeled from current ome
• speed increases each time so can approach speed of light
• collide w fixed target at end of tube

Question 24

Whats a synchrotrons?

Answer 24

-circular accelerator w two beams in opposite directions so can produce very high energy collisions

Question 25

When speed of object is approaching c it…

Answer 25

Gets more massive

Question 26

How does the fact that electrons are fermions effect there energy levels?

Answer 26

Means no more than 2 electrons cqn be in the same energy level at the same time

Question 27

How do wave models of atoms help us understand energy levels?

Answer 27

-when they orbit a nucelus follow pattern of standing wave
-one orbit fits n lambda like standing waves
-think lf electrons like being trapped in a potential well so can be represend by two walls showing energy levels
-electrons can escape when KE+PE>0
Diameter of atom (distance between walls) to ifnd de brogile wavelength