P3 Topic 4 - Motion Of Particles Flashcards
In practice, how do charged particles behave in a magnetic field?
They move in a spiral until they stop at the centre. This is because a magnetic field always acts perpendicular to the direction of travel of the particle, causing it to turn. As the particle moves, it loses speed as it interacts with other particles and this is why is spirals in.
What two forces act on an object travelling in a circle?
Give an example with a satellite orbiting Earth.
Centrifugal and Centripetal
Velocity keeps the satellite from crashing into the Earth and gravity stops it from flying of at a tangent into space.
How does a cyclotron work?
A cyclotron is a particle accelerator that has two semicircular electrodes with opposite charges.
The charged particle, usually a proton starts in the middle and is attracted to one of the two electrodes.
An alternating current is then passed through the electrodes causing them to change their polarity, the proton is now attracted to the other electrode.
As it moves from one side to the other, it gains energy and therefore speed and starts to spiral outwards until it is fired out of the accelerator at a target.
What’s the difference between an elastic and an inelastic collision?
An elastic collision conserves momentum and kinetic energy, no energy is lost.
In an inelastic collision, some energy is lost, through heat or sound etc.
Explain positron/electron annihilation.
When a particle meets its antiparticle, all their mass is converted in energy which given off as gamma radiation.
As they tend to collide head on and travelling at the same speed, the total momentum is zero as their velocities cancel out. Therefore, their overall momentum is conserved after the collision.
Due to the conservation of momentum, the gamma rays coming out of the annihilation must also have a momentum of zero, meaning that they come out at perpendicular angles of the particles. They have the same energy but opposite velocities
