PHYS 0970 1st Edition Exam # 3 Study Guide Lectures: 22 - 32RC CircuitsMagnetic FieldsCaused by moving charges which creates a currentRight hand rule (two types)Causes centripetal accelerationHelical PathsPitch-only function of v|| (analogous to the range in constant horiozontal velocity over time from a parabolic motion)Radius-relation to mass, centripetal velocityCrossed magnetic and electric fields/particle selectorPerpendicular to eachotherNet force=0; particle moves straight lineIf positive charge, if Electric field is stronger, will move toward negative plate;If positive charge and magnetic field is stronger towards positive plate(unwillingly)Hall EffectMagnetic force moves electrons to one sideCreates potential differenceCharges will deflect to more stable side(less repulsion or more attraction)Will in turn create an electric fieldHall voltagesTorque on Current LoopNet translational force is zeroNonzero torqueBiot-Savart LawIntegrating nonsymmetrical Ampere’s lawMust have cylindrical symmetry, preferably constant radius or electric fieldLine integralClosed loopSuperposition-apply multiple times at a point P if there are multiple wires-must have a constant radius in order for constant magnetic fieldGauss’ Law for flux magnetic fieldZero-because equal and opposite, Can’t isolate magnetic poles(dipole)Measures number of magnetic field lines through area-normal to surfaceFor each turn multiply by N turns for totalCircular Loop of WireSome components will usually cancel due to symmetry|| Conductors|| wireswires in same direction attract, opposite(anti parallel 180) direction repel1 source wire, 1 test wireaction rxn pair- forces == and oppwire hanging from wire problemcannot neglect gravity and tensionSolenoidsOnly a constant magnetic field on inside(in a rectangular loop)(if ideal, length is much greater than diameter)else the magnetic field will decrease by the edgesOutside-B=0Perpendicular(also 0) because of ampere’s law-dot productToroidal solenoid=solenoid into a circleToroid and solenoid-both same result for magnetic fieldThe length of solenoid is the same thing as the circumference of the circleOutside-B=0 net because currents equal and opposite enclosedInside/ r<R if amperian loop inside the inner current of opposite direction, also 0 current enclosed(no field)SLenz’s and Faraday’s Laws-induced Emf(potential difference)Changing flux induces emfSince a voltage is induced, and V=Ed, then there is an induced electric field“negative feedback”prevents too drastic of an increase or decrease by inducing a magnetic field in the opposite directionMotional emfMight need integrate the flux and differentiate dx/dt=vpower dissipatedPmech=Pheat(due to resistance)P=dW/dtMutual InductanceOnly depends on geometryIndependent of current(will cancel)M=strength of coupling “sensitivity”Affected by magnetic field produced by otherTherefore, if only have area of one, say that since the field is only due to that one, can use the area of that one to calculate magnetic field since it is the same amount of enclosed current i(if the area is greater than the area for which current is enclosed in)Neglect self inductances(L)Self Inductance/Inductance definedRL circuitEnergy stored in magnetic fieldOnly a function of field
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