# 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

- Created by: Ravina
- Created on: 08-03-11 09:18

First 271 words of the document:

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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