Topic 4 - Motion of Particles Flashcards
How does circular motion work?
- Velocity is speed + direction of object
- If object travelling in circle it’s constantly changing direction so accelerating
- Must be a resultant force on it
- Force acts towards centre of circle
- Force keeping object moving in circle called centripetal force
What is the force that keeps an object moving in a circle?
Centripetal force
How are charged particles affected by a magnetic field?
- Experience a force
- Force on a moving charge in magnetic field perpendicular to direction of travel so follows curved track
- Direction of force on particle depends on charge (paths of +ve and -ve charge curve in opposite directions
- Usually moves in spirals as particle loses energy + slows down as interact w/ other particles
- Less energy = more curve (smaller spiral)
- Magnetic fields make charged particles move in circular or spiral path in particle accelerators
How does a cyclotron work?
- Charged particles (e.g. protons) start at centre of cyclotron
- Uses 2 hollow semi-circular electrodes to accelerate particles across a gap
- Alternating potential difference applied between electrodes as particles are attracted from one side to another energy increases (accelerated)
- Magnetic field used to keep particles moving in a circular motion
- MAgnetic field makes particles spiral outwards as energy increases
What is a cyclotron?
A particle accelerator which uses a magnetic field to accelerate particles to v. high energies along circular paths
How can proton enrichment be used to form radioactive isotopes?
- Bombarding nucleus w/ protons
- Proton absorbed by nucleus
- Increases proton no. so new element forms
- Proton needs lots of energy to be absorbed by nucleus so process takes place in cyclotron
What do radioisotopes formed from proton enrichment usually do and what can they be used for?
- Usually positron emitters
- Positron emitters useful in hospitals (PET scanning)
- Important radioactive isotopes for PET scanning have short half-life so patient’s exposure to radiation is minimised
How can particle accelerators be used to find out about the universe?
- Use particle accelerators to smash particles into each other at v. large speeds to see what happens (what radiation given off, what new particles created)
- Shows how univers works so can develop better explanations of physical world
Why does research into particle physics, using particle accelerators, have to be done collaboratively?
- Particle accelerators expensive, not every country can afford one
- Useful to combine expertise + specialists
What problems can be caused from collaborative work with particle accelerators?
Rival groups looking for the same thing + want to be first
Give one example of collaborative working with particle accelerators.
- Large Hadron Collider, Geneva
- Built by European Organization for Nuclear Research (CERN)
- Largest + most powerful ever built
- Scientists use it to try to recreate conditions just after Big Bang by colliding 2 beams of protons head on at fast speeds
What is the equation for momentum?
mass x velocity
What situations are there demonstrating the conservation of momentum?
- Collision, bouncing off: e.g. when fast moving neutron hits nucleus + bounces off again
- Collision, joining together: e.g. neutron/proton colliding w/ atom + absorbed by nucleus
- Explosion, shot + recoil: e.g. particle being emitted from a nucleus, nucleus recoils like a fired gun
What is an elastic collision?
One where momentum is conserved + kinetic energy conserved (no energy dissipated as heat, sound)
What is an inelastic collision?
One where some of the kinetic energy is converted into other forms, but the momentum is conserved
How does a ball collide with the ground?
- Inelastic collision
- Drop ball + bounces but not so high as where 1st dropped
- When dropped GPE transfers to KE, when hits ground loses some KE as heat/sound, hence inelastic collision
- Ball loses KE so less to transfer to GPE when back up
- Investigate factors affecting rebound height of ball by changing: material, surface dropped on OR initial height
When does annihilation occur?
- When a particle meets its antiparticle
- All masses of both particles converted to energy given off in form of gamma rays
What happens when an electron and positron meet?
- Collide head on at same speed in opposite directions
- Have same mass + opposite velocities so total momentum before collision = 0
- Momentum conserved so gamma rays have 0 momentum
- Usually happens in 2 gamma rays w/ same energy + opposite velocities
- Charge before + after must be =, before = 0 + after = 0; charge conserved
What equation shows how mass-energy is conserved in annihilation reactions?
Energy [E, joules, J] = mass [m, kg] x c^2 [speed of light, 3x10^8]
What can positron/electron annihilation be used for?
- PET scanning
- Positron emitting isotope injected to patient
- Emitted positrons collide w/ electrons in organs so annihilate + emit high energy gamma rays
- Higher take up of radio isotope in tumour cells than normal cells
- Detectors around body detect each pair of gamma rays; tumour lies along same path as each pair
- Through detecting at least 3 pairs tumour can be accurately located through triangulation
