Particle

Question 1

Rutherford’s Alpha Scattering Experiment

Answer 1

Setup:
Alpha source fired alpha particles at very thin gold foil.
Detectors set up around it
Observations:
Most alpha went straight through
Some deflected
(Very) few came straight back/large angle
Conclusions:
Atom mainly (empty) space
Nucleus contains most of the mass
(Nucleus) very small/tiny
(Nucleus) charged /positive

Question 2

Thermionic Emission

Answer 2

Using heat to cause electrons to be released

Question 3

The equation for the force on a charged particles at a right angle to a B field

Answer 3

F = BQv

Question 4

The equation for the force on a charged particle in an E field

Answer 4

F = kQq/r^2

Question 5

Describe the role of E and B fields in a cyclotron?

Answer 5

Electric fields:
Electric field provides force on the charge/proton
gives energy to /work done / E = qV/ accelerate
protons
Magnetic fields:
Force on moving charge/proton
Produces circular path/centripetal force

labelled diagram showing Dees
with E field indicated across gap OR B field through Dees
E field is reversed/alternates

Question 6

Role of E fields in LINACs

Answer 6

Protons drift/move uniformly inside tubes
Accelerate between the tubes/in the gaps
Alternating p.d. reverses while p is in tube
The tubes must get longer as p speeds up
For time inside tube to be constant or to synchronise
movement with the pd

Question 7

Nucleon Number

Answer 7

Protons + Neutrons in nucleus

Question 8

Proton Number

Answer 8

Number of protons in the nucleus

Question 9

Role of B & E Fields in detectors

Answer 9

Electric fields
• can be used to accelerate/deflect particles
• direction of force/deflection indicates (sign of) charge.
• a = EQ/m
Magnetic fields
• produce circular motion Or provides a centripetal force Or causes
spirals/arc
• Direction of force/curvature/deflection indicates (sign of) charge.
• momentum/speed/mass found from radius/curvature
• r = p/BQ Or Bqv = mv
2
/r

Question 10

Derive r= p/BQ

Answer 10

Centripetal force, F = mv^2/r
Force in a particle perpendicular to magnetic field, F = BQv

mv^2/r = BQv => mv/r = BQ => r = mv/BQ 
p = mv => r = p/BQ

Question 11

What properties are conserved in a particle interaction?

Answer 11

Lepton number, baryon number, electric charge, strangeness

Question 12

What do particle tracks show?

Answer 12

They show where a particle has been, by measuring their radius and direction - properties should as momentum or charge can be investigated

Question 13

Why are high energies used in Particle Accelerators

Answer 13

High energy needed to break particles into constituents and/or create new particles (1)
High energy linked to short wavelength, e.g. λ = h/p (1)
Short wavelength comparable to dimensions of structures / mention of diffraction (1)
High energy needed to get close to nuclei (1)
To create particle /antimatter
Or To allow (large) repulsive forces to be overcome
Or To break the particles (into their constituents)

Question 14

What equation links energy and mass

Answer 14

E = mc^2

Question 15

What is it called when a photon splits into two particles?

Answer 15

Creation

Question 16

What happens when a particle and its antiparticle collide?

Answer 16

Anniliation

Question 17

Define an electron volt

Answer 17

Energy gained by an electron when accelerated through a potential difference of 1V - 1.6 x 10^-19J

Question 18

Define eV/c^2

Answer 18

E = mc^2

1 eV = m * (9x10^16)
1.6x10^-19J/(9x10^16) = m = 1.78266191 × 10-36 kilograms

Question 19

When is relativistic lifetime significant

Answer 19

When things are travelling close to the speed of light then lifetime increases due to relativistic effects

Question 20

Define Baryon

Answer 20

A baryon is a particle made up of 3 quarks or antiquarks

Question 21

Define Meson

Answer 21

A meson is a particle made up of a quark-antiquark pair

Question 22

Define Lepton

Answer 22

A lepton