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# Science P3 Topic 4

### GCSE edexcel further additional physics: motion of particles

Why do scientists looking into particle physics collaborate? * brings together expertise from around the world * shares the cost of the experiments
How can particle accelerators help scientists to develop better explanations about the physical world? particle accelerators can help scientists study and discover new particles as they create very high speed collisions which may produce new particles
What must there be for motion to occur in a circle? For motion in a circle there must be a resultant force called a centripetal force that acts towards the centre of the circle
What are cylotrons? Particle accelerators
How do cyclotrons work? -charged particles move in a circular/spiral path -a magnetic field produces a centripetal force (90º) -alternating voltage accelerates charged particles -charged particles spiral outwards + travel in a straight line when leaving cyclotron
What are cyclotrons used for? Small cyclotrons are used to produce the isotopes with short half-lives needed in PET scanners
What is momentum + what type of quantity is it? Momentum is the amount of mass in motion or how difficult it is to stop a moving object, measured in kilogram metre per second- kg.m/s. It is a vector quantity, so has a size and a direction (the direction of the velocity)
What is an elastic collision? In an elastic collision, both momentum and kinetic energy are conserved
What is an inelastic collision? In an inelastic collision, momentum is conserved but kinetic energy isn’t conserved, as some of it is transferred to thermal and sound energy
What would happen if the collision between a green ball moving at 3m/s and a stationary yellow ball was: a) elastic b) inelastic? ELASTIC: The green ball would stop moving and the yellow ball would move at the same, constant velocity as the green ball was moving, i.e. same direction, 3m/s. INELASTIC: Many choices e.g yellow ball may move away at 2m/s when the green ball stops
A 200kg car travels at 4m/s, crashes into 100kg bike travelling at 1m/s- if the car keeps going in the same direction at 2m/s, what is the speed of the bike after the collision?
What is anti matter? Anti-matter is matter composed of anti-particles that have the opposite charge but the same mass as the corresponding particle
What happens when an electron collides with its anti-matter particle? When an electron and a positron collide, they annihilate each other, producing two gamma rays that move in opposite directions
What is the concept of mass-energy equivalence? Mass-energy equivalence explains that mass-energy has been conserved, as the mass of the particles is converted into an equivalent amount of energy
How do you calculate the energy produced in a collision? Energy (joules) = mass (kg) x speed of light^2 (3 x 10^8 ms^-1)... E = mc^2
Show that mass-energy is conserved in positron-electron annihilation Mass-energy before = 1.6 x 10-13J, because the mass of an electron is 9 x 10-31kg, so its energy equivalent is 9 x 10^-31kg x (3 x 10^8)^2 x2 for positron. Mass-energy after = 1.6 x 10-13J, because this is the total energy of two gamma rays
Show that momentum is conserved in positron-electron annihilation Momentum before = 0, because if the electron and positron approach each other at the same speed, they have equal but opposite momentum. Momentum after = 0, because the gamma rays have energy (a mass equivalent) and are moving in opposite directions
Show that charge is conserved in positron-electron annihilation Charge before = 0, because an electron has a -1e charge and a positron has a +1e charge. Charge after = 0, because gamma rays carry no charge.
How are radio isotopes used in medicine? PET scanners- radio isotopes that emit positrons injected into blood in tracer, which accumulates in tissues. positrons annihilate when meeting electrons. gamma rays detected by sensors. the time difference between detection of gamma rays produces image
Created by: 11043