H2_Electromagnetism_Lecture_Notes_(Teachers)

9749 H2 PHYSICS Lecture Notes Nanyang Junior College 1 Chapter 16 ELECTROMAGNETISM Content • Concept of a magnetic field • Magnetic fields due to currents • Force on a current-carrying conductor • Force between current-carrying conductors • Force on a moving charge 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 flux patterns due to currents in a long straight wire, a flat circular coil and a long solenoid (c) use B = µ0I / 2πd, B = µ0NI / 2r and B = µ0nI for the flux densities of the fields due to currents in a long straight wire, a flat circular coil and a long solenoid respectively (d) show an understanding that the magnetic field due to a solenoid may be influenced by the presence of a ferrous core (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 F = B Il sinθ, with direc tions as interpreted by Fleming’s left-hand rule (g) define magnetic flux density and the tesla (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 (j) predict the direction of the force on a charge moving in a magnetic field (k) recall and solve problems using the equation F = BQvsinθ (l) describe and analyse deflections of beams of charged particles by uniform electric and uniform magnetic fields (m) explain how electric and magnetic fields can be used in velocity selection for charged particles

9749 H2 PHYSICS Lecture Notes Nanyang Junior College 2 1 Magnetic Field The idea of a field is a theoretical concept used by scientists to explain how objects interact with one another without physically touching each other. Field lines (flux patterns) are imaginary lines which aid visualization and quantification of the field. A magnetic field is a region of space in which a magnetic material, a current -carrying conductor or a moving charge located in it may experience a force. Magnetic field lines are lines of force as they indicate the direc tion of the force acting on a magnetic North pole. If the lines of force are parallel, the field is uniform. This means that the number of lines passing perpendicularly through unit area at all cross -sections in a magnetic field is the same. If the lines of force are closer together, the field is said to be stronger. Magnetic field lines do not intersect as there can only be one direction for the field at any point. Co