P=i^2r=vi

[Jeff85]

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When does power double(P=IV) with a doubling of current and when does it quadruple from a doubling of current(P=I^2R)

 

[Eye Cue]

Depends on the question because you have to figure out which other variable is kept constant.

 

[Vanguard23]

If it's asking about voltage and current, use the relevant equation. If it's about resistance and current, use the relevant equation. At least, that's worked for me pretty well.
If you decrease resistance, you decrease power by that amount *however*, you also have more current going into that resistor and the effect is going to be squared. So that has a net increase in power.

 

[fizzgig]

if you're just confused by the equation you set up, the answer is, i guess, it's always going to be the current squared factor.

P=I^2R=IV=I(IR) -- your P=IV eqn still has I*I=I^2 in it because of ohms law V=IR.

 

[Jeff85]

what about voltage squared or not?(P=IV=V^2/R)
what about resistance being directly proportional to power or inversely proportional depending on which equation used?

 

[Eye Cue]

.

 

[traitorman]

I see where you are getting confused. It looks like power is doubled in one equation while it is quadrupled in another. This is not the case.

To understand this, choose two random values for I and V and solve for R. For example, if I = 2 and V= 10, R will equal 5 (using V=IR).

Plug those values into any 3 of these equations and power is the same in all three:

P = IV = 2x10 = 20
P = I^2R = 20
P = V^2/R = 20

The equations are all related and are written that way to keep the consistency when you are switching between V, I, and R values.

 

[traitorman]

In general, you have to look at the resistors to determine what you are looking for.

1) If you have several resistors in series, the current that passes through each of them is the same so current is constant.
The one with the bigger resistance = bigger Voltage = bigger power. (for series)

2) If you have several resistors in parallel, the voltage through each of them is the same so V is constant.
The one with the bigger resistance = smaller I = smaller power. (for parallel)

 

[puravida85]

When does power double(P=IV) with a doubling of current and when does it quadruple from a doubling of current(P=I^2R)

I think I know what you're asking. But, I think what you mean to ask is, when to use P equals IV or P equals I squared R? Sorry the schools keyboard is messed up, no functioning equal button.

We use P equals I V when we want to find the power supplied by the circuit by voltage source. Meaning, this is the capable power from the entire circuit. While P equals I squared R is used to find the power dissipated by a particular resistor. Hope that helps.

 

[thamsenman]

P = IV applies to the battery or the voltage of an individual resistor. The battery has a specific voltage itself.

P= (I^2)*R can apply to either the Power of the circuit if R = the combination resistance or it can be the power burned by a single resisitor in a circuit if R is the resistor in question.