* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download CH 8: Magnetic Fields
Survey
Document related concepts
Maxwell's equations wikipedia , lookup
Introduction to gauge theory wikipedia , lookup
History of subatomic physics wikipedia , lookup
Elementary particle wikipedia , lookup
Field (physics) wikipedia , lookup
Condensed matter physics wikipedia , lookup
Magnetic field wikipedia , lookup
Electromagnetism wikipedia , lookup
Neutron magnetic moment wikipedia , lookup
Magnetic monopole wikipedia , lookup
Superconductivity wikipedia , lookup
Aharonov–Bohm effect wikipedia , lookup
Transcript
CH 8: Magnetic Fields 8.4 – Motion of Charged Particles in Magnetic Fields Agenda Warm Up / Homework Check Clicker Questions from yesterday Lesson on Section 8.4 Textbook Questions Learning Goals Analyse and solve problems involving the motion of charged particles in magnetic fields Warm Up Question A 155mm part of a wire has a mass of 0.30kg and carries an electric current of 3.5 A. The conventional current passes through a uniform magnetic field of 2.5 T. The direction of the wire and the magnetic field are shown in Figure 7. A. What is the magnitude of the magnetic force on the wire? B. Use the right-hand rule to determine the direction of the magnetic force. Warm Up Question Earth’s magnetic field exerts a force of 1.4 x 10-5 N on a 5 cm segment of wire in a truck motor. The motor wire is positioned at an 23° angle to Earth’s magnetic field, which has a magnitude of 4.9 x 10-5 T at the truck’s location. Calculate the current in the wire. 4. Clicker Question 5. Clicker Question 7. Clicker Question 8. Clicker Question 9. Clicker Question Mass Spectrometer http://www.youtube.com/watch?v=_L4U6I mYSj0 Motion of a Charged Particle in a Magnetic Field v v v F F F v Magnetic force provides the centripetal acceleration. Motion of a Charged Particle in a Magnetic Field If m, q and B are held constant, higher speed larger radius. 2r r 106 m/s F1 2x106 m/s F2 Example A Bainbridge mass spectromoter is used to measure the mass of zinc ions (Zn+). The ions enter a magnetic field, of strength B=1.8T with a speed of 4.2 x 104 ms-1 and they move in a circular path of radius r = 1.7cm. What is the mass of the zinc ions? An electron in a magnetic Field An electron starts from rest. A horizontally directed electric field accelerates the electron through a potential difference of 40V. The electron then leaves the electric field and moves into a magnetic field. The magnetic field strength is 0.T, directed into the page (Figure 3), and the mass of the electron is 9.11 x 10-31 kg. A. Determine the speed of the electron at the moment it enters the magnetic field. B. Determine the magnitude and direction of the magnetic force on the electron. C. Determine the radius of the electron’s circular path. Mass Spectrometer: Separating Isotopes Cyclotron Particle Accelerator http://www.youtube.c om/watch?v=cNnNM 2ZqIsc TRIUMF National laboratory in Vancouver has the largest cyclotron at 18m Use of Magnetic Fields in Cyclotrons Particles moving in a cyclotron are subjected to a uniform magnetic field which causes the particles to move in a circular path. Each time the charged particle enters a Dee it follows a semi-circular path and each time it traverses to the other Dee its speed is greater than before as it is subjected to an Electric field. Its energy has increased by W=qV. Use of Magnetic Fields in Cyclotrons The period of the charged particle is independent of its speed, this can be shown by the following, Circumfere nce of a circle, C 2r (length of one semicircle r ) time to traverse one semicircle r t v mv but r qB rqB v m rm m thus t rqB qB time taken to complete one full revolution 2m t qB Use of Magnetic Fields in Cyclotrons The Kinetic Energy can be found by, Ek 1 2 mv 2 rqB 2 m m q 2 B 2r 2 2m 1 2 mv as r qB Use of Magnetic Fields in Cyclotrons Example, A cyclotron is used to accelerate dueterons (q = 1.6 x 10-19C) of mass 3.34 x 10-27 kg. The radius of the cyclotron is 30cm and the magnetic field applied to it has strength 1.6T. Find (a) The period of the particles in their circular path. (b) The energy (in eV) of the particles leaving the cyclotron. Use of Magnetic Fields in Cyclotrons (a) The period of the particles in their circular path. 2m T qB 2 3.34 10 27 1.6 10 19 1.6 8.2 10 8 s Use of Magnetic Fields in Cyclotrons (b) The energy (in eV) of the particles leaving the cyclotron. q 2 B 2r 2 K 2m (1.6 10 19 ) 2 (1.6) 2 (0.3) 2 2 3.34 10 27 8.83 10 13 J change into eV 8.83 10-13 1.6 10 19 5.52 106 eV 5.52 MeV Homework pg. 404 #2-6 Quiz on Chapter 8 Tomorrow?