Review II - 1 Exam II Review Phys2020 Don't forget: • , (if no friction) netFm=GGaKE PE∆=−∆ • : E-fieldsGptcharge2kQEr=G, tot 1 2EEE..=++GGG (E-fields add like vectors) • Voltage: pt chargekQVr= , tot 1 2VVV=++E⋅∆.. (voltages add like numbers) • , ∆=, on qFq=GGof qPE q VV E x (when E is parallel to x)∆=⋅∆ ∆GG +Q Capacitors area A d R I ∆V hi V lo V • capacitance QCV= • C depends only on size and shape: oACdε= • stored energy = 2211 1QUQVCV22 2== =C • energy per volume = 2oU1uEvolume 2==ε⋅ Circuits • Ohm's Law: ∆= V I R (where R = constant) • Resistance of a resistor: LRAρ= ρ = resistivity = measure of internal friction, depends on composition –Q E V = ∆V area A LReview II - 2 • 22WVpower P I V I RtR∆====∆ • Equivalent Resistance: Rtot = R1 + R2 R2 R1 = in series: R1 R2 =in parallel: totR = 12111RR+0 Things that are always true in circuits: • elements in series always have the same current: • elements in parallel always have the same voltage: • voltage change along an unbroken ideal wire is zero (since we assume Rwire = 0 ) : wire wireVIR I0∆= =⋅= • ideal battery means constant ∆V, any current (current depends on the circuit) R1R2I I R3 I I RbigVRsmallIsmallIbig∆V sameacross both R'sReview II - 3 I2 • K's Current Law (Junction Law) total current into junction = total current out of junction : 12II=+3I • K's Voltage Law (Loop Law) total voltage change around any closed loop is zero • Ammeters and Voltmeters • AC vs. DC Vrms = Vpeak / √2 Irms= Ipeak / √2 P = I V ⇒ Ppeak = Ipeak Vpeak and Pavg = Irms Vrms V = I R ⇒ Vpeak = Ipeak R and Vrms = Irms R Magnetism • Currents cause magnetic fields (B-fields) • BBFFqvBsin qv⊥== θ =GBFG "right-hand-rule" • When both E-field and B-field are present: GG Ntot E BqEFF=+G • B-field due to long straight wire: 0IB 2rµ=πB=+GGG • B-field is a vector: BB tot 1 2I1 I1 I3 junction junctionB
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