Different power equations

[MrNeuro]

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I was wondering when it is proper to use the different Power equations

P=IV=I^2R=V^2/R

i know for I^2R when current is the same so for a circuit with resistors in series so what does that mean about the voltage its changing???

V^2/R when Voltage is the same across resistors so for a circuit with resistors in parallel aka current is varrying

but what about P=IV when do you use this???

 

[milski]

They are virtually the same. Use whichever is more convenient. If you have I and V given, use P=IV instead of trying to calculate R first.

 

[MrNeuro]

They are virtually the same. Use whichever is more convenient. If you have I and V given, use P=IV instead of trying to calculate R first.

when can you have I and V for a series circuit but not for a parallel circuit unless you calculate all the individual currents and add them up or if you just calculated the total R and divided it by the V i guess im sort of answering my own question here thanks

 

[411309]

For a series circuit you use P=I^2R which shows that in series larger resistors dissipate more power, for parallel circuits you can use P= V^2/R to show that smaller resistors disspate more power.

 

[MrNeuro]

For a series circuit you use P=I^2R which shows that in series larger resistors dissipate more power, for parallel circuits you can use P= V^2/R to show that smaller resistors disspate more power.

and P=IV when you have total current and voltage?

 

[milski]

when can you have I and V for a series circuit but not for a parallel circuit unless you calculate all the individual currents and add them up or if you just calculated the total R and divided it by the V i guess im sort of answering my own question here thanks

Yes, for series you have to calculate the individual Vs, it's much easier to use I since it is the same for all of the resistors. It's really nothing but pluggin V=IR in P=IV.

 

[MrNeuro]

thanks

 

[MedPR]

It's the same idea as the kinematics equations.

If they give you acceleration, final velocity, and initial velocity and tell you to find displaement, you're going to use v^2=vo^2+2ax. You COULD use x=vot+1/2at^2, but that would involve a second step since you don't have the time.