Transcript f=2450 MHz
Test 2 results 18 16 Number of Students 14 12 10 8 Series1 6 4 2 0 1 >90 2 >80 3 >70 4 >60 Score Average 65.2 Median 68 Highest 99 Lowest 8 5 >50 6 >40 7 Electron motion in a microwave oven A magnetron in a microwave oven emits electromagnetic waves with frequency f=2450 MHz. What magnetic field strength is required for electrons to move in circular paths with this frequency? Using Crossed E and B Fields Velocity selector qvB qE 0 E vB E v B independent of the mass of the particle! Mass spectrometer m1v R1 qB v E B m1 E R1 qB 2 m2 E R2 qB 2 Thomson’s e/m experiment 1897: Cavendish Laboratory in Cambridge, England 1 2 2eV mv eV v 2 m E v B E 2eV e E2 B m m 2VB 2 Exercise 1 An electron, q=1.6 10-19C moves with velocity 5 5 v 6 10 ix 4 10 iy in meters per sec ond 2 B 0 . 1 i webers / m It enters a magnetic field with x What is the force on the electron? Problem 5 Hall effect: The magnetic force on the charge carries in a wire can be used to determine their sign. Show that there will be an electric field, set up inside a wire in a magnetic field, that is perpendicular to the direction of the current. You should be able to show that the sign of the field depends on whether the mobile charges are positive or negative. qE Hall qvB i v nAq EHall iB jB nAq nq You place a slab of copper, 2.0 mm thick and 1.5 cm wide, in a uniform magnetic field with magnetic field with magnitude 0.40 T. When you run a 75-A current in the +x direction, you find by careful measurement that the potential at the left side of the slab is 0.81V higher than at the right side of the slab. From this measurement, determine the concentration of mobile electrons in copper. Current carrying wires 1820 Hans Christian Oersted Hans Christian Ørsted Exercise 3 A wire of length l and mass m is suspended as shown. A uniform magnetic field of magnitude B points into the page. What magnitude and direction would a current, passing through a wire, have to have so that the magnetic and gravitational forces would cancel?