P3.4 Motion of particles Flashcards
What is particle physics?
The study of subatomic and fundamental constituents of matter
What are sub-atomic particles?
Particles smaller than atoms
What are fundamental particles?
Particles that cannot be broken down into smaller units
What particles are thought to be fundamental?
Quarks, anti-quarks, electrons and positrons
How do scientists test new theories and models in particle physics?
They repeat experiments and critically evaluate the work published in science journals
What is the LHC?
A particle accelerator
Why is a particle accelerator used?
To collide particles at high energies to break them down into smaller ones
What does circular motion require to keep moving in a circle?
A centripetal force
What is a resultant force?
The total force from two or more forces acting on a single object
How do you find the resultant force?
By adding the forces together while taking into account their direction
What is a centripetal force?
A resultant force acting inwards along the radius
What happens when an object travelling in a circular motion loses its centripetal force?
It travels in a straight line at a tangent to the circular path it was following
What provides a centripetal force?
Tension
Why is an object moving in circular motion accelerating even though the speed doesn’t change?
Because it is constantly changing direction
What are cyclotrons?
Particle generators which bend moving charged particles into circular or spiral paths
What produces the centripetal force required in a cyclotron?
A constant magnetic field applied at right angles to the particles motion
What are the magnetic field regions in a cyclotron shaped as?
D-shaped
What does the voltage in a cyclotron do?
Accelerate the charged particles
Where is the voltage placed in a cyclotron?
Across a gap between the two D-shaped magnetic field regions
What happens to the path of particles in a cyclotron as their speed increases?
It spirals outwards
What happens once particles leave a cyclotron?
They travel in a straight line towards a specific target
What happens when a high-energy proton collides with a stable element?
The nucleus can change into an unstable nucleus of a different element
What is a radioactive isotope?
An unstable isotope that emits radiation
What produces the short-lived isotopes used in PET scanners?
Small cyclotrons
What type of collision does a ball dropped on the ground undergo?
Inelastic collision
What is inelastic collision?
A collision where kinetic energy is not conserved
What can kinetic energy in an inelastic collision be transferred as?
Heat or sound energy
What is kinetic energy?
Movement energy
Why does a ball not rebound to the same height after it’s been dropped?
Because kinetic energy has been transferred so it’s not the same as before
What does LHC stand for?
Large Hadron Collider
What is the formula for calculating momentum?
p = mv Momentum = mass x velocity
What is momentum?
A measure of the strength of movement
What happens to momentum in all collisions?
It is conserved
What happens to kinetic energy in an elastic collision?
It is conserved
What is a vector?
Something that has both a size and a direction
What type of value for momentum will an object moving backwards or to the left have?
Negative
What is momentum measured in?
Kg m/s
What is anti-matter?
Matter that has particles of the same mass and properties as their counterparts but opposite electrical charges
What is the anti-matter of an electron?
A positron
What happens when an electron and positron collide?
Total annihilation of the particles and the production of two gamma rays that move in opposite directions
What do the basic conservation laws of physics apply to?
Mass, momentum and energy
What is mass-energy equivalence?
The idea that destroyed mass can be converted into an equivalent amount of energy in order to obey conservation laws
Who came up with the idea of mass-energy equivalence?
Einstein
What is the formula for calculating the energy of a system from something that uses mass-energy equivalence?
E = mc^2
Energy of a system = mass x the speed of light squared
What is the speed of light?
3 x 10^8 ms^-1
What is the mass of an electron?
9 x 10^-31 kg
What is the energy equivalent of the mass of an electron?
8 x 10^-14 J
What is the total amount of energy released from a positron-electron annihilation?
1.6 x 10^-13
What does PET scanner stand for?
Positron emission tomography scanner
What does the radioactive tracer a person about to receive a PET scan emit?
Positrons
How are gamma rays produced in a PET scanner?
From the collision of positrons from the tracer and electrons from the scanner
How does a PET scanner locate where a tracer has come from?
Through triangulation; it detects the two gamma rays emitted in opposite directions and can calculate where it came from
