PHYSICS – Electricity: Formulas 3.0 / 5 PhysicsD.C. ElectricityASAQA Created by: Amy HillsCreated on: 21-04-13 13:40 Current (measured in amps [A]) I=Q/t I=V/R I=P/V 1 of 11 Voltage (measured in volts [V]) V=W/Q V=IR V=P/I (W=energy) 2 of 11 Resistance (measured in ohms [Ω]) R=V/I R= ρXL/A ρ=resistivity L=length in m A=cross-sectional area in m² Resistors in series: R= R1+R2+R3... Resistors in parallel: 1/R= 1/R1+1/R2+1/R3... 3 of 11 Resistivity (measured in ohm-metres [Ωm]) ρ=RXA/L 4 of 11 Power (measured in watts [W]) P=VI P=V²/R P=I²R 5 of 11 Total Energy (measured in joules [J]) E=VIt E=(V²/R)t E=I²Rt Basically: powerXtime=total energy 6 of 11 Conservation of energy energy per coulomb supplied by source= energy per coulomb used in load resistance+energy per coulomb wasted in internal resistance the energy wasted per coulomb overcoming the internal resistance is called the lost volts (v) 7 of 11 Root mean square (rms) of an alternating current a Irms=1/√2 XV0 Vrms=1/√2 X I0 ie. rms= peak/√2 V0=voltage peak value I0=current peak value 8 of 11 Electromotive force (E.M.F) [V] and internal resis ε =E/Q ε =V+v ε =I(R+r)=IR+Ir V=ε-v V=ε-Ir v=lost volts V=terminal p.d E=electrical energy r=i.r R=load resistance 9 of 11 Power in an alternating current P= Irms2R P=Vrms2/R P=VrmsX Irms 10 of 11 Resistance in alternating current R=Vrms / Irms = V0 / I0 11 of 11

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