When to use P=I*V or P=I^2*R

[StayingFocused]

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Can someone explain to me what the difference is between these two equations and when should you use either one. Thank you.

 

[sciencebooks]

Can someone explain to me what the difference is between these two equations and when should you use either one. Thank you.

You can also write it as P=(V^2)/r

Notice it's just a rearrangement of the equation P=IV by subsituting it either "V/R" for I or "IR" for V (from Ohm's law).

Basically, I'm under the impression that you use the formula in which you have values for BOTH components of the equation.

 

[xxEmily]

You can also write it as P=(V^2)/r

Notice it's just a rearrangement of the equation P=IV by subsituting it either "V/R" for I or "IR" for V (from Ohm's law).

Basically, I'm under the impression that you use the formula in which you have values for BOTH components of the equation.

Yup... whichever one is fastest.

If you're given a value of I and a value of R, use P = I^2*R.

If you're given a value of I and a value of V, use P = I * V

You'd get the same answer of P converting say V to R by using the formula R=V/I and using the P=I^2*R formula. But if you can just use P=I*V then why waste time? That's why it's useful to memorize the different forms of that formula, for the sake of time, but it's not necessary per se if you at least have 1 form memorized along with V=IR.

 

[ebasappa]

Don't get caught in the trap, however, when given a graph to compare the Power and Current in a circuit. In that matter, you use P=IV (linear graph) over P=i^2R, because the voltage stays constant! So if you raise Current, the Resistance would decrease, making the second formula wrong. Someone correct me if I'm wrong though!

 

[curt656]

V = I R

P = (I^2) R or stated another way: P = I I R

therefore P = V I

 

[V5RED]

Don't get caught in the trap, however, when given a graph to compare the Power and Current in a circuit. In that matter, you use P=IV (linear graph) over P=i^2R, because the voltage stays constant! So if you raise Current, the Resistance would decrease, making the second formula wrong. Someone correct me if I'm wrong though!

Resistance is a physical property of the resistor/resisting material. Raising current will not affect resistance.

 

[richkaj]

P# VR... P=IV, P=IR, P=I^2R, P=V^2/R... Help me out if P=VR

 

[sciencebooks]

Don't get caught in the trap, however, when given a graph to compare the Power and Current in a circuit. In that matter, you use P=IV (linear graph) over P=i^2R, because the voltage stays constant! So if you raise Current, the Resistance would decrease, making the second formula wrong. Someone correct me if I'm wrong though!

Yeah, I remember seeing a question on this. I know you can't use P=(i^2)R because if current is changing, then obviously that could change voltage by V=IR. Something like that, but I can't remember exactly.