Ch+20+-+Magnetism

> ** Topics ** > > Induced EMF & Magnetic Flux > **__ Induced EMF & Magnetic Flux __** > -Induced EMF is produced by changing a magnetic field! > -Faraday first conducted an experiment that demonstrated that an electric current can be produced by a // changing magnetic field. // -What effects the EMF? Magnetic Flux and time > -Magnetic Flux is similar to an electric flux and is proportional to both the strength of the magnetic field passing through the plane of the loop and the area of the loop. > -The value of the magnetic flux is proportional to the total number of lines passing through the loop. > -Units of Magnetic Flux: Tm^2=Wb > > > > **__ Faraday's Law of Induction __** > -A current is set up in the circuit as long as there is relative motion between the magnet and the loop. > -Hence, an induced current is produced by an induced EMF. > - E=-N(∆Flux/∆t) > > > **__ Motional EMF __** > -an EMF induced in a conductor moving through a magnetic field > ∆V=El=Blv > -A potential difference is maintained across the conductor as long as there is motion through the field. If the motion is reversed, the polarity of the potential difference is also reversed. > -If bar moves distance of ∆x in time ∆t, then E can be expressed as: > |E|=(∆flux/∆t)=Bl(∆x/∆t)=Blv > -If resistance of a circuit is R, then the induced current in the circuit is: > I=|E|/R=(Blv)/R > > > **__ Lenz's Law __** > -states that the induced current tends to maintain the original flux > -provides physical interpretation of the choice of sign in Faraday's Law of induction, indicates that induced emf and the change in flux have opposite signs > > > ** Generators ** > > -Alternating current (AC) generator: device that converts mechanical energy to electrical energy > -AC consists of a wire loop rotated in a magnetic field by some external means. > -Total induced emf can be found by E=2Blv=2Blvsinø > -Direct Current (DC) generator: device that has similar components as an AC generator, except the contacts to the rotating loop are made by a split ring, or commutator. > -A motor is a generator run in reverse. The current is supplied to the loop by a source of emf.-Back emf= used for an emf that tends to reduce the applied current.
 * ||||||||||~ __ Electricity & Magnetism __
 * Faraday's Law of Induction
 * Motional EMF
 * Lenz's Law
 * Generators
 * Self-Inductance
 * RL Circutis
 * Energy Stored in a Magnetic Field

-Circuit with resistor, as the switch closes the current increases. As the current increases, the magnetic flux through the loop increases. As the flux increases it induces an emf opposite the change in magnetic flux. The same thing happens when the switch is opened. -Self induced emf is produced by the circuit itself -Equation: E=-L(∆i/∆t), L=inductance, measured in Henry's, depends on the cross sectional area of the coil, 1H=1 Vs/A
 * Self Inductance**

RL Circuits -Inductors= circuit element with large inductance, closely wrapped coil -The image below represents what the symbol of an inductor looks like. > > > > > > > > -Energy stored in an inductor: PE=(1/2)(Li^2) -Energy stored in a capacitor: PE=(1/2)C(∆V)^2
 * Energy Stored in a Magnetic Field**

> table that I found that has all of the E & M units that we are using. > > electromagnetism units || > ||~ Symbol ||~ Name of Quantity ||~ Derived Units ||~ Unit ||~ Base Units || > || //I// || || A || A (= W/V = C/s) || > || //Q// || Electric charge || coulomb || C || A·s || > || //U//, Δ//V//, Δ//φ//; //E// || Potential difference ; Electromotive force || volt || V || J/C = kg·m2·s−3·A−1 || > || //R//; //Z//; //X// || Electric resistance ; Impedance ; Reactance || ohm || Ω || V/A = kg·m2·s−3·A−2 || > || //ρ// || Resistivity || ohm metre || Ω·m || kg·m3·s−3·A−2 || > || //P// || Electric power || watt || W || V·A = kg·m2·s−3 || > || //C// || Capacitance || farad || F || C/V = kg−1·m−2·A2·s4 || > || //**E**// || <span class="wiki_link_ext">Electric field strength || <span class="wiki_link_ext">volt per <span class="wiki_link_ext">metre || V/m || N/C = kg·m·A−1·s−3 || > || //**D**// || <span class="wiki_link_ext">Electric displacement field || <span class="wiki_link_ext">Coulomb per <span class="wiki_link_ext">square metre || C/m2 || A·s·m−2 || > || //ε// || <span class="wiki_link_ext">Permittivity || <span class="wiki_link_ext">farad per <span class="wiki_link_ext">metre || F/m || kg−1·m−3·A2·s4 || > || //χ//e || <span class="wiki_link_ext">Electric susceptibility || (dimensionless) || - || - || > || //G//; //Y//; //B// || <span class="wiki_link_ext">Conductance ; <span class="wiki_link_ext">Admittance ; <span class="wiki_link_ext">Susceptance || <span class="wiki_link_ext">siemens || S || Ω−1 = kg−1·m−2·s3·A2 || > || //κ//, //γ//, //σ// || <span class="wiki_link_ext">Conductivity || <span class="wiki_link_ext">siemens per <span class="wiki_link_ext">metre || S/m || kg−1·m−3·s3·A2 || > || //**B**// || <span class="wiki_link_ext">Magnetic flux density, Magnetic induction || <span class="wiki_link_ext">tesla || T || Wb/m2 = kg·s−2·A−1 = N·A−1·m−1 || > || //Φ// || <span class="wiki_link_ext">Magnetic flux || <span class="wiki_link_ext">weber || Wb || V·s = kg·m2·s−2·A−1 || > || //**H**// || <span class="wiki_link_ext">Magnetic field strength || <span class="wiki_link_ext">ampere per <span class="wiki_link_ext">metre || A/m || A·m−1 || > || //L//, //M// || <span class="wiki_link_ext">Inductance || <span class="wiki_link_ext">henry || H || Wb/A = V·s/A = kg·m2·s−2·A−2 || > || //μ// || <span class="wiki_link_ext">Permeability || <span class="wiki_link_ext">henry per <span class="wiki_link_ext">metre || H/m || kg·m·s−2·A−2 ||