Lecture Physics A2: Magnetic fields - PhD. Pham Tan Thi present the content analysis model particle in a magnetic field, magnetic field lines, magnetic force, an electron moving in a magnetic field, representations of magnetic field lines perpendicular to the page, . | Magnetic Fields Analysis Model Particle in a Magnetic Field q In our study of electricity we described the interactions between charged objects in terms of electric fields. Recall that an electric field surrounds any electric charge. In addition to containing an electric field the region of space surrounding any moving electric charge also contains a magnetic field. A magnetic field also surrounds a magnetic substance making up a permanent magnet. Magnetic Field Lines q Magnetic filed lines outside the magnet point away from the north pole and toward the south pole. Magnetic Force q The existence of a magnetic field at some point in space can be determined by measuring the magnetic force F exerted on an appropriate test particle placed at that point. q If we perform an experiment by placing a particle with charge q in the magnetic field Magnetic Force q The magnetic field is defined in terms of the force acting on a moving charged particle q The magnitude of the magnetic force on a charged particle is Electric Field vs Magnetic Field q SI unit of magnetic field is tesla T An Electron Moving in a Magnetic Field q An electron in an old-style television picture tube moves toward the front of the tube with a speed of x 106 m s along the x axis Fig. . Surrounding the neck of the tube are coils of wire that create a magnetic field of magnitude T directed at an angle of 60 to the x axis and lying in the xy plane. Calculate the magnetic force on the electron. An Electron Moving in a Magnetic Field Representations of Magnetic Field Lines Perpendicular to the Page Motion of a Charged Particle in a Uniform Magnetic Field q The magnetic force on the particle is perpendicular to both the magnetic field lines and the velocity of the particle. q The particle changes the direction of its velocity in response to the magnetic force whereas the magnetic force remains perpendicular to the velocity. q If the force is always perpendicular to the velocity the path of the
