Forces on Charged Particles Flashcards
electric fields
imagine a test positive charge
outwards from positive
inwards towards negative
what is a force field
a region where an object experiences a force without being touched
eg: gravitational, magnetic, electric
uniform fields
closer together=stronger force
further away a particle gets, less strength of field acting on it
field lines in parallel plate equally spaced
what does a charged object create?
an electric field
what happens when a charged particle moves
it will also produce a magnetic field
what will happen if a charged particle is in a magnetic field?
it will experience a force
what does each finger represent in the right hand rule?
index - magnetic field
middle - direction of particle
thumb - direction of force
left or right for a positively charged particle
left
left or right for a negatively charged particle
right
what does x mean
into the page
what does o mean
out of page
how can something accelerate and travel at constant speed?
change in velocity - either magnitude or direction
particle follows curved path, constantly changing direction
eg: roundabout
what does it say about the magnetic field if there is no change in velocity of the electron
the magnetic field must be parallel to the motion of the electron
what path does electron follow if force is at right angles?
circular path
what happens to kinetic energy if direction is changing
velocity is changing but magnitude of velocity stays the same so Ek=1/2mv squared remains the same
if a negative charge moves through an electric field from negative to positive, the energy will appear as…
kinetic energy
if a positive charge is moved from negative to positive then work has to be done. the energy is stored as…
electric potential energy
change in potential energy=
work done
work done in electric field equation
W=QV (v=E/Q)
once the charge is released…
the electric potential energy is converted into kinetic energy
moving charges in electric fields equation
QV=1/2mv squared (QV=Ek)
what are particle accelerators?
devices that use electric and magnetic fields to accelerate charged particles to very high speeds for particular purposes
example of particle accelerator
cathode ray tubes used in older-style televisions/computer monitors
Types of particle accelerators
- linear accelerator
- circular accelerators
- synchrotrons
The Large Hadron Collider
27km of tunnels on the France-Switzerland border with massive detectors placed at various points along its route
Cathode ray tubes
large glass tubes that contain a particle accelerator
types include: deflection tubes, Maltese cross tubes or Perrin tubes
how cathode ray tubes work
an electric field between the cathode and anode causes electrons to be accelerated from one to the other
linear accelerators (linacs)
a charged particle is attracted towards a plate in a ‘drift’ tube
the particle passes through one of these tubes and is then accelerated towards the next and so on.
the field between each drift tube must change rapidly so that each new tube attracts the particle leaving the previous tube
kept in centre by series of magnets but in order to increase the energy and velocity of the particle, the accelerator needs to be big. (eg: longest is Stanford Linear Accelerator in California)
circular accelerators (cyclotron)
work by using a series of magnets to keep the particles in a circular orbit. this allows high-frequency voltage supply to accelerate the particles
can be smaller and therefore cheaper
comprises two D-shaped sections with a small gap and a very high potential difference between them
a charged particle is accelerated across the gap then bent inside one of the dees until it is in the opposite direction. It accelerates across the gap again and process is repeated until particle has correct energy
as particle becomes faster, path radius increases and it moves out towards the edge of the dees. at very high speeds, relativistic effects interfere with the efficient operation of the cyclotron and it can become difficult to adapt the fields in line with the particle.
Synchrotrons
synchrotron radiation is emitted under the conditions mentioned before and this can lead to energy loss in particle physics experiments
we can build the synchrotron such that the radiation is produced at certain frequencies for scientific/medical purposes
specific type of circular accelerator where magnetic and electromagnetic fields have been adapted to produce a very energetic and narrow ring of charged particles at very high energies
many synchrotrons produce high energy x-rays for spectroscopy where structure of atoms are investigated
examples of synchrotrons
The Large Hadron Collider and the Fermilab in the USA (massive and extremely expensive)
