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Physics 220 Final
|Faraday's Law in Words
|The emf around a loop equals the rate at which the magnetic flux within the loop is changing. emf=-dBFlx/dt
|3 ways to change flux
|-Change B in a loop -Change area of loop -change orientation of loop
|looping electric field lines
|Faraday’s Law - The source of looping electric field lines is changing magnetic flux.
|The direction of induced current always opposes the change in magnetic flux.
|Commutators and Brushes AC DC
|These allow electrical connections to be made by pressing conductors together. -Uses double commutators(sinusoidal wave) -Bouncing wave
|The Split Commutator
|changes the end of the loop connected to the positive terminal of the battery every half cycle (DC)
|Motor operated in reverse
|a coil of wire placed in a circuit. usually solenoidal or toroidal windings. - oppose change in circuits.
|An Inductor in a DC Circuit
|produces a B field and the wire has a resistance.
|An Inductor in an AC Circuit
|Changing current continually, hence, changing B field, self inductions
|LR CIrcuits resistor is large Inductor is large
|-takes shorter time for current to decrease, decreases induced current -better at making induced current, takes longer for induced current to decrease
|Kirchoff's Loop Law
|The voltage around the loop at any given time must be zero. q(t)=Asin(wt)+Bcos(wt) q(t)=CVocos(wt) at max
|Initially the capacitor is charged. No current flows as the inductor initially prevents it. Energy is in the electric field of the capacitor
|Measures voltage as a function of time Usually used for waves with repeated waveforms Starts a trace when the wave has a certain value Can compare two voltages Sometimes can show single pulses also
|wL has a role that is similar to resistance – it relates voltage to current. XsubL Large at high f
|1/wC - XsubC Large at low f
|when inductive reactance = capacitive reactance
|Circuit Rules for AC Circuits - Parallel
|1-their voltage phasors are the same. 2-their current phasors add to give the total current
|Circuit Rules for AC Circuits - Series
|1-their current phasors are the same. 2-their voltage phasors add to give the total voltage.
|the combined “effective resistance” of circuit elements.
|effective AC current
|change in electric flux
|The displacement current term is called “Maxwell’s Term” in Ampère’s Law The amount of magnetic field lying along a closed (Amperian) loop is proportional to the rate at which electric flux through the loop changes.
|The amount of electric field lying along a closed (Amperian) loop is proportional to the rate at which magnetic flux through the loop changes. looping electric
|The amount of magnetic field lying along a closed (Amperian) loop is proportional to the current passing through the loop. looping b
|Gauss's LAw of Magnetism
|The net number of magnetic field lines passing through a closed (Gaussian) surface is zero. spreading b
|Gauss's Law of Electricity
|The net number of electric field lines passing through a closed (Gaussian) surface is proportional to the charge enclosed. spreading E
|Fields of Accelerating Charges1
|Moving charges produce both electric and magnetic fields Acceleration fields are “doglegs” in field lines produced when charges accelerate.
|Fields of Accelerating Charges2
|Acceleration fields become perpendicular to the direction the filed moves. Acceleration fields fall off as 1/r rather than 1/r 2.
|Characteristics of Radiation
|Produced by accelerating charges Perpendicular to the direction the field moves. Fall off as 1/r rather than 1/r 2 Emax=cBmax
|power per unit area or energy/area/time.
|about same frequency
|The external field needed to bring the internal field back to zero
|When the external field goes to zero, some domains remain aligned
|Any voltage, as from a battery effective voltage produced by an induced electric fields accel charges - changing curent in circuit motional emf -charges in a conductor moving in field.
|Have a constant value of electric potential (voltage) everywhere on the surface Are perpendicular to the field everywhere Are closer together where the field is stronger when we make a set of surfaces separated by equal voltage differences