area AdRIVhi Vlo VReview II - 1Exam II Review Phys2020Don't forget: netF m a=rr,KE PED =- D (if no friction) E-fieldsr: pt charge2k QEr=r, tot 1 2E E E ..= + +r r r (E-fields add like vectors) Voltage: pt chargek QVr= , tot 1 2V V V= + +.. (voltages add like numbers) on qF q E=r r, of qPE q VD = �D,V E x (when E is parallel to x)D = �D Drr Capacitors capacitance QCV= C depends only on size and shape:oACde= stored energy = 221 1 1 QU Q V C V2 2 2 C= = = energy per volume = 2oU 1u Evolume 2= = eCircuits Ohm's Law: V I R (where R = constant)D = � Resistance of a resistor:LRAr= +Q–QEV = Varea ALin series:R1R2=Rtot = R1 + R2R1R2=in parallel:Review II - 2 = resistivity = measure of internal friction, depends on composition 22W Vpower P I V I Rt RD= = = =D Equivalent Resistance: tot1 21R1 1R R=+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 (sincewe assume Rwire = 0 ) : wire wireV I R I 0 0D = = � = ideal battery means constant V, any current (current depends on the circuit)R1R2I IR3IIVRbigRsmallIsmallIbigV sameacross both R'sReview II - 3 K's Current Law (Junction Law) total current into junction = total current out ofjunction : 1 2 3I I I= + 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 / 2P = I V Ppeak = Ipeak Vpeak and Pavg = Irms VrmsV = I R Vpeak = Ipeak R and Vrms = Irms RMagnetism Currents cause magnetic fields (B-fields) B BF F q v B sin q v B^= = q =r "right-hand-rule" When both E-field and B-field are present: {tot E Bq EF F F= +rr r r B-field due to long straight wire: 0IB2 rm=p B-field is a vector: tot 1 2B B B= +r r rI2I3I1I1junction junctionI
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