AQA A physics electricity formulae

various formulae from the electricity topic, the majority of which are on the formula sheet but make sure to familiarize yourself with them

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  • Created on: 08-03-11 09:18
Preview of AQA A physics electricity formulae

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PHYSICS ­ Electricity:
Formulas, need to know!
· Current (measured in amperes/amps [A]):
I=Q/t I=V/R I=P/V
· Voltage (measured in volts [V]):
V=W/Q (W=energy) V=IR V=P/I
· Resistance (measured in ohms []):
R=V/I R= XL/A
=resistivity L=length in m A=crosssectional area in m²
Resistors in series: R= R1+R2+R3...
Resistors in parallel: 1/R= 1/R1+1/R2+1/R3
· Resistivity (measured in ohmmetres [m]):
=RXA/L
· Power (measured in watts [W]):
P=VI P=V²/R P=I²R
· Total Energy (measured in joules [J])
E=VIt E=(V²/R)t E=I²Rt Basically: powerXtime=total energy
· Conservation of energy:
energy per coulomb = energy per coulomb + energy per coulomb wasted
supplied by source used in load resistance in internal resistance
· the energy wasted per coulomb overcoming the internal resistance is called the lost
volts (v).
· Electromotive force (E.M.F) [measures in volts] and internal resistance:
=E/Q =V+v =I(R+r)=IR+Ir V= v V= Ir
v=lost volts V=terminal p.d E=electrical energy r=internal resistance R=load
resistance
· Root mean square (rms) of an alternating current and pd.:
Irms=1/2 XV0 Vrms=1/2 X I0 ie. rms= peak/2
where V0=voltage peak value I0=current peak value
· Power in an alternating current:
P= Irms2R P=Vrms2/R P=VrmsX Irms
· Resistance in alternating current:
R=Vrms / Irms = V0 / I0

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