RI Chap 17 Electromagnetic Forces Lecture Notes

17 ELECTROMAGNETIC FORCES H2 Physics 9478 Content Page 17.1 Concept of a Magnetic Field 2 17.2 Magnetic Fields Due to Currents 5 17.3 Force on a Current-Carrying Conductor 9 17.4 Forces Between Current-Carrying Conductors 15 17.5 Force on a Moving Charge 19 17.6 Motion of a Charged Particle in a Magnetic Field 20 17.7 Appendix 26 Learning Outcomes Candidates should be able to: (a) show an understanding that a magnetic field is an example of a field of force produced either by current carrying conductors or by permanent magnets (b) sketch magnetic field lines due to currents in a long straight wire, a flat circular coil, and a long solenoid (c) use 0 2B d µ π= I , 0 2 NB r µ= I and B = µ0nI for the magnetic flux densities of the fields due to currents in a long straight wire, a flat circular coil, and a long solenoid respectively [Not in H1 syllabus] (d) show an understanding that the magnetic field due to a solenoid may be influenced by the presence of a ferrous core [Not in H1 syllabus] (e) show an understanding that a current -carrying conductor placed in a magnetic field might experience a force (f) recall and solve problems using the equation sinF BIL θ= , with directions as interpreted by Fleming’s left-hand rule (g) define magnetic flux density as the force acting per unit current per unit length on a conductor placed perpendicular to the magnetic field (h) show an understanding of how the force on a current-carrying conductor can be used to measure the flux density of a magnetic field using a current balance (i) explain the forces between current-carrying conductors and predict the direction of the forces [not in H1 syllabus] (j) predict the direction of the force on a charge moving in a uniform magnetic field. (k) recall and solve problems using the equation sinF BQv θ= . (l) describe and analyse deflections of beams of charged particles by uniform electric fields and uniform magnetic fields. (m) explain how perpendicular electric and magnetic fields can be used in velocity selection for charged particles

Page | 2 17.1 Concept of a Magnetic Field  Properties of Magnets • Natural magnets were discovered from ancient archaeological sites more than two thousand years old. The term ‘magnet’ comes from the name of one of the locations these stones were found. • Experiments have shown that (i) magnetic poles are of two kinds, i.e. north (N) or south (S), (ii) like poles repel each other, unlike poles attract, (iii) poles occur only in opposite pairs (dipoles), (iv) when no other magnet is near, a freely suspended magnet will rotate so that the line joining its poles is approximately parallel to the Earth’s axis of rotation, and (v) the pole of the magnet that points towards the Earth’s Geomagnetic North is called the north pole of the magnet and the other the south pole of the magnet.  Magnetic Field • Forces between magnets can be explained using the concept of a magnetic