EECS 210: Analogies between electricity and water flow Winter 2001

### ANALOGIES BETWEEN ELECTRICITY AND WATER FLOW

Don't take these too literally, but they are illustrative and suggestive.

QuantitySymbolUnitsWhat it isAnalogueUnits
ChargeqCoulombsElectric chargeWaterGallons
Currenti=dq/dtAmperes=
coulomb/sec
Flowing charge Water flowGallons
per second
VoltagevvoltsElec. potentialwater pressurepsi
Resis-
tance
R=v/i
v=iR
Ohmsneed a field to
move a charge
ResistancePressure
drop:pipe
Conduc-
tance
G=i/v
G=1/R
backwards)
need a field to
move a charge
conductancePressure
drop:pipe
Ideal wireR=00 OhmssuperconductorIdeal pipeno friction
Voltage
source
Vsv=constantideal battery or
ideal generator
constant pres-
sure pump
water
tower
Current
source
Isi=constantideal solar cell constant velo-
city pump
fountain
Capacitori=
Cdv/dt
ated
charge
Water tower
(stores water)
Gallons,
or height
Inductorv=
Ldi/dt
netic field
NoneNone
EnergyW=qvJoulesTo move charge
across voltage
Potential
energy
PE=(mg)h

Another perspective, using height instead of pressure as analogous to voltage:

QuantityWhat it isWater Analogue
KCL (current law)conservation of chargewater flow in=water flow out
Negative currentactual flow other wayactual flow is the other way
Resistors in seriesR=R1+R2Resistance increases w/length
Resistors in parallelG=G1+G2Pipes in parallel increase flow
Voltage (another way)Electrical potentialHeight (gravitational potential)
Kirchhhoff's (KVL)
Voltage Law
potential is path-indpt
in electric circuits
takes same energy to reach
a height regardless of path
Ground potentialReference voltageSea level
Node voltageVoltage at a pointHeight above sea level