Réponse 1:

C'est la même chose que la différence entre la force et l'énergie dans tout autre contexte.

La force elle-même a la capacité de travailler, c'est-à-dire de fournir de l'énergie, mais elle ne le fait que lors du déplacement d'un objet. L'énergie fournie est alors la force multipliée par la distance parcourue.

Inelectricalterms,theforceFisequaltothestrengthoftheelectricfield,[math]E[/math],timesthechargethattheelectricfieldisactingon,[math]Q[/math]:In electrical terms, the force F is equal to the strength of the electric field, [math]E[/math], times the charge that the electric field is acting on, [math]Q[/math]:

F=EQ\qquad F=EQ

Butagain,thisforcebyitselfjusthasthepotential(hencetheworditself!)toprovideenergy.Energyisonlydeliveredwhentheforceresultsinmovementofthecharge.Theenergyprovidedisthen,asinthegeneralcase,theforcetimesthedistancedmoved.So:But again, this force by itself just has the potential (hence the word itself!) to provide energy. Energy is only delivered when the force results in movement of the charge. The energy provided is then, as in the general case, the force times the distance d moved. So:

energy=EQd\qquad \text{energy}=EQd

Nowwhilstthisiscorrect,werenotusedtodealingwithelectricalenergyinthisway.Howeverwecaneasilytranslatethisintoamorefamiliarform.Letssaythatwhenmovingthroughdistancedthatthechargemovesthroughavoltagedifferenceof[math]V[/math].Inthiscasethefieldstrength[math]E=Vd[/math].Sonowwehavethat:Now whilst this is correct, we’re not used to dealing with electrical energy in this way. However we can easily translate this into a more familiar form. Let’s say that when moving through distance d that the charge moves through a voltage difference of [math]V[/math]. In this case the field strength [math]E=\frac{V}{d}[/math]. So now we have that:

energy=VdQd=VQ\qquad energy =\frac{V}{d}Qd=VQ

IfthishappensrepeatedlyeverytimeperiodTthenwehavethatthepowerdeliveredis:If this happens repeatedly every time period T then we have that the power delivered is:

P=energyT=VQT\qquad P=\frac{\text{energy}}{T}=V\frac{Q}{T}

ButQTischargepassingperunittime,whichisofcoursejustcurrent.Sowenowhavetheveryfamiliarresult:But \frac{Q}{T} is charge passing per unit time, which is of course just current. So we now have the very familiar result:

P=VI\qquad P=VI