MEDI 11002 Lecture Notes - Lecture 7: Electronvolt, Wave, Electron Gun
ELECTRIC AND MAGNETIC FIELDS
Force on charges in magnetic fields
- The magnetic force on an electric current is due to the force on the moving
charges
- The magnitude of the force on a charge moving at speed is given by:
ī”²īƤīµīīī”®ī
- Charges moving freely at right angles to a magnetic field will move in a circular
path
Particle accelerators
- In a particle accelerator, charged particles are always accelerated, sometimes to
speeds close to the speed of light
- A cathode ray tube is a simple particle accelerator in which particles accelerate
from a hot cathode to a high-voltage anode
o An electron gun is the source of the electrons in a cathode ray tube and
many particle accelerators
o An electron may be accelerated across a potential difference, such as in
the case of an electron accelerating towards an anode in a cathode ray
tube
o The electron experiences a force:
īØ īµ ī īīæīø
ī
As the electric field strength is equivalent to
ī§ īµ ī īæīø
ī
- The work done on an electron of charge accelerating across this potential
difference is ī¢īÆīµ īīæīø
- The increase in kinetic energy of an electron with mass is ī”±īÆīµ ī ī¬µ
ī¬¶īīī¬¶īµ īīæīø
- For the case when the electron is moving at right angles:
ī”²īƤīµīīī”®ī
If the magnetic force is the net force acting on the electron, it will move in a
circular path of radius r:
ī īµ ī īī
īī”®ī
- A linear accelerator (or linac), accelerates particles in straight lines. The standing
wave linac is generally used to accelerate low-energy ions and the travelling
wave linac is used in the Australian synchrotron, is employed to accelerate
electrons.
Synchrotrons
- A synchrotron is a doughnut shaped particle accelerator designed to circulate
electrons around a closed path at speeds very close to that of light
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The magnetic force on an electric current is due to the force on the moving charges. The magnitude of the force on a charge moving at speed is given by: Charges moving freely at right angles to a magnetic field will move in a circular (cid:2162)=(cid:1869) path. In a particle accelerator, charged particles are always accelerated, sometimes to speeds close to the speed of light. As the electric field strength is equivalent to. The work done on an electron of charge accelerating across this potential: the electron experiences a force: (cid:1832)= (cid:1869) (cid:1831)= difference is =(cid:1869) . The increase in kinetic energy of an electron with mass is (cid:2161)= (cid:2869)(cid:2870)(cid:2870)=(cid:1869) (cid:2162)=(cid:1869) (cid:1870)= (cid:1869) . If the magnetic force is the net force acting on the electron, it will move in a circular path of radius r: For the case when the electron is moving at right angles: A linear accelerator (or linac), accelerates particles in straight lines.
Ā 106Ā m/s is projected along the axis midway between the deflection plates of a cathode-ray tube. The uniform electric field between the plates has a magnitude of 1.34Ā 
