Chapter 19 Magnetism Hard magnetic material difficult to magnetize Retain magnetism permanent Soft magnetic material easy to magnetize lose magnetism easily Magnetic field Defined by force felt by test charge moving with velocity v Motion if a charged particle in a magnetic field the magnetic force is always directed toward the center of the circular path therefore the magnetic force causes a centripetal acceleration which changes only the direction of vS and not its magnitude Magnetics field due to a long straight wire Chapter 20 Induced Voltages Inductance Moving charges can generate a magnetic field Moving magnet induce electric current INDUCED EMF changing magnetic field MAGNETIC FLUX magnetic field lines perpendicular B BAcos Btwn normal n B Perpendicular only Torque on Current loop BIANsin Bsin B at angle perpendicular to the plane of the loop Amperes Circuit Law Two long parallel wires apart carry the same current and the magnetic force per unit of length each wire 2 10 7 Amperes when 2 parallel 1m apart carry the same current and magnetic force per unit length each wire is Magnetic force between wires Parallel conductors carrying currents in the same direction attract each other Parallel conductors carrying currents in opposite directions repel each other MAX BIA EXAMS Q s Slinky battery switch closed I runs will not compress expand will heat up insead N B t Generator motor run in reverse loop roated by external means Emf insuced into loop makes current AC generator Total emf 2Bl a2 sin t BA Sin Lenz s Law current caused by the induced emf making B that oppose the original change in flux thro circuit F B qvBsin T 1 Gauss 10 4 used only when current magnetic field are at right angles to one other Magnitude of Magnetic Force Faraday s Law Can cause change in magnetic flux 1 loop A 2 B3 angle btwn A n B Magnetic field of a current loop BA Wb weber Tm2 V B x I Bl t t L t Blv Motional emf Blv I R R Solenoid electromagnet inside Self inductance change in flux is from circuit Self induced emf l N B i Inductance of a Solenoid o N 2 A l 2 o n A l o n 2 V n N l L Energy stored in magnetic field Emf from inductor prevents battery from setting instantaneous current in circuit energy stored in magnetic field 1 PE L L I 2 2 max NBA V max Sin t RL Circuits Inductor on solenoid measure rate of change of current Time constant Vs A HENRY H L inductance NBA Sin t L R Trandformers Increasing current in primary creates an increase in flux thro primary secondary Faradays law Inductive reactace Large currents can be generated with small Vrms Induced emf Flux same through coils Transformers depend on change in flux only work for alternating currents Higher V smaller I less power wasted Properites of EM E B fields are perpendicular then perpendicular to direction of motion EM WAVES TRANSVERSE WAVES particle a it radiates energy lose energy in EM waves Inductor L voltage E comes before current I Capacitor C current I comes before voltage E Phase shiV is 90 degrees for both Chapter 21 Alternating Current Circuits and Electromagnetic Waves Resistors in an AC Circuit DC battery power source V constant AC ac poer source generator V Vmaxsin 2 f Vrms IrmsR Vmax ImaxR iR vR R R is constant for all frequences Power RMS value Direction of I no effect on R P i2R rate of electrical energy dissipated in circuit Rms current is direct current dissipates the same amount of energy in the resistor as it was dissipated by the AC current Irms I max 2 Ohm s Law for R in AC Switch is close intitail charge in capacitor is 0 Charge accumulate on V develops opposing I High f less t to charge c high I Pav I2rms R or V RMS I rms R V max sin2 ft The reactance depends on the frequency of the source Current and voltage don t go together Current is same for all components in series Resonant Frequency XL XC so Z R The power dissipated in an AC series ciruit incease as the phase ang e approaches what value zzero EM wave ttravel thro free space speed cannot increase by f energy momentum E B perpendicular