Topic 4-Motion of particles Flashcards
(22 cards)
What does it mean if an object is traveling in a circle and what force does this result in
It is constantly changing direction
Is therefore accelerating
There must be a resultant force which acts towards the centre of the circle called the centripetal force
The force on a moving charge in a magnetic field is
Perpendicular to its direction of travel, causing the particle to follow a curved track
What does the direction particles travel in a magnetic friend depend on
Positive or negative charge (opposite directions)
Why do you see particles moving in spirals
Because particles lose energy as they interact with other particles
Less energy=more curved
Why are magnetic fields used in particle accelerators such as cyclotrons
To make the particles move on a circular or spiral path
What is a cyclotron
A particle accelerator which uses a magnetic field to accelerate particles at very high energies along circular paths
How does a cyclotron work
1) charged particle starts in centre
2) two semicircular electrodes used to accelerate across gap
3) alternating potential difference applied between electrodes-particle attracted from one side to the other causing energy to decrease
4) the magnetic field maintains circular motion
5) causing particles to spiral out as energy increases
What does proton enrichment form
Isotopes that emit positrons
How does positron enrichment work
A proton is absorbed by nucleus causing the proton number to increase forming a new element
This needs a lot of energy (cyclotron used)
Radioisotopes formed by proton enrichment are positron emitters
Good in hospitals (PET scans)
Give three examples of radioisotopes formed by proton enrichment
Fluorine-18
Carbon-11
Nitrogen-13
How do particle accelerators help scientists find out more about the universe and some problems with this
Use them to smash particles together at tremendous speeds to see what happens to give clues
Done internally, is expensive and need specialist expertise
Rival groups looking at the same thing
Example of collaborative work using proton enrichment
Large Hadron Collider at Geneva
CERN built the largest and most powerful accelerator to recreat collisions after the Big Bang
Momentum is always
Conserved
In elastic collisions
Momentum and kinetic energy is conserved
In Inelastic collisions
Some kinetic energy is converted into other forms
Momentum is always conserved
An example of Inelastic collisions and how kinetic energy is converted
Bouncing ball
Won’t bounce as high as you dropped it as gravitational potential energy is transferred into kinetic energy and lost when hits the ground (sound/heat)
MOMENTUM=
MASS*VELOCITY
What is the mass of both particles converted into and given of as in annihilation
Into energy which is given of as two gamma rays
What happens in positron and electron annihilation
The position and electron collide head on at the same speed, opposite directions
They have the same mass and opposite velocities so momentum is 0
Momentum is conserved so the two gamma rays have a momentum of 0
So the gamma rays produced have the same energy but opposite velocities
Why is the charge before and after annihilation 0
Electrons have a negative charge and positrons have a positive charge (-1,+1)
Gamma rays have no charge
How is annihilation used in PET scanning
Positron emitting radioactive isotope is injected which collided with electrons in organs (annihilate—>gamma rays)
There is a higher take up in tumour cells than normal ones
Detectors around body detect pair of gamma rays which tumour lays along the path of
Detect three pairs to accurately locate tumour by triangulation
What is velocity
Speed and direction of an object
