Motion of Charged Particles Pg

Mass Spectrometer  Atoms and molecules are the building blocks of our universe………..but how do scientists study these particles?  Mass spectrometers are used:  because they are able to define the elemental composition of a sample or molecules  to determine the masses of particles  to reveal the chemical structures of molecules  How does it work??

Mass Spectrometer  An instrument that can separate particles of different mass and, in fact, measure that mass  The first stage is a velocity selector:  A beam of particles having different velocities, as a result of carrying different charges, is “filtered” so that only those particles with the same velocity continue

Mass Spectrometer  Then, ions of the selected speed enter a magnetic field in a direction perpendicular to the field  While in the magnetic field, the ions experience a magnetic force that is perpendicular to the direction of their motion (centripetal force)

Mass Spectrometer  So really……. It is separating particles of different mass by analyzing: FC = FM mv 2 = qvB r So…… m = rqB v

Mass Spectrometer

Practice

Bubble Chamber  A bubble chamber (similar in design to a mass spectrometer) is used to study the trajectories of elementary particles (electrons/protons)  The diagram shoes the trajectories of some typical particles  Looking at the white arrow – the particle follows a curved path due to the presence of a magnetic field perpendicular to the plane of the photo

Practice  3. Suppose the particle identified is moving in the direction indicated by the green arrow and the magnetic field is directed into the page.  A) does the particle have a positive or negative charge?  Positive because its direction is the same as that predicted by the right-hand rule  B) describe how the trajectory changes when the mass is decreased by a factor of 10.  r / 10 (r is proportional to m)  C) describe how the trajectory changes when the charge on the particle is increased by a factor of 3  r x 1/3 (inversely proportional)

Field Theory  We associate the term force with the PHYSICAL action of one object on another (i.e. a bat and a baseball) BUT…  There are spatial gaps between atoms in a bat and a baseball so the idea that they are actually making contact is deceptive In reality….  Electromagnetic forces affect the interacting atoms in each object  How to we explain the interaction of these forces?

Field Theory  A scientific model that describes force in terms of entities, called fields, that exist at every point in space  Field theory can be applied in explaining the minute interactions of subatomic particles as well as describing the motions of galaxies throughout the universe

Field Theory  Studying gravitational, electrical, and magnetic forces has revealed differences and similarities between these forces and their respective fields  The electric and magnetic fields have a stronger effect on the motion of subatomic particles but the gravitational field has a stronger effect on large objects such as planets and galaxies

Field Theory  Despite these similarities and differences, field theory states that electric and magnetic fields are more closely related to one another than they are to the gravitational field  …..they even think that electric and magnetic fields are just different aspects of a single field  They are used in conjunction with each other in a variety of technologies (particle accelerators…..even artificial hearts)

Textbook  Pg. 404, #1, 3  Pg. 405 “Applications of Electric and Magnetic Fields  - read and make brief notes on:  RFID chips  MR Fluid Dampers  High-voltage power lines  Medical applications