Calculating electrical energy over time

[anj16]

Hello,

Let's say I am generating 5 amp at a constant 1 volt and storing it in a battery without any loss of energy. The question is what am I adding to the battery? Am I adding power as a function of time or is it something else? So say if I were to calculate how much energy has accumulated after 5 hours how would I do that?

Thank you.

 

[russ_watters]

P=VI
E=PT

Power is energy added per unit time.

 

[anj16]

Ah I see, thank you.

 

[technician]

Amp means coulomb per second. Volt means Joule per coulomb.
therefor V x I means Joules per second = power.
power x time = energy in Joules

 

[anj16]

What if my voltage isn't constant? Doesn't that mean that my power isn't constant either? And doesn't E=PT rely on constant power?

 

[technician]

you would then find yourself talking about 'instantaneous power'. If the voltage changes presumably the current also changes.
An interesting example is in AC circuits where V and I are changing and can be out of step.

 

[anj16]

what do you mean by instantaneous power? Wait do you mean to take the integral of the power function with respect to time?

 

[milesyoung]

What if my voltage isn't constant? Doesn't that mean that my power isn't constant either?

Sure.

And doesn't E=PT rely on constant power?

You're right again. $E(t) = \int_{t0}^t P(\tau) \mathrm{d}\tau$ is true in general.