# Physics Equations for Electrical Power

• coordinators
In summary, Russ says that the equation that the OP is asking for is not the correct one, but that there is a discussion about how to combine Ohm's law and the electrical power equation in various ways for various purposes.f

#### coordinators

I'm in year 11, doing Physics for GCSE and my actual ending GCSE is on Friday which Is where I finish school.

I'm 16 and in the UK, I need help with the following equations:
P = I^2 x R (why is this equation used)
- all the power equations
- How to calculate uncertainty

<< Mentor Note -- OP has edited this post to correct the equation. See Russ' quote below for the original equation that Russ is replying about >>

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I'm 16 and in the UK, I need help with the following equations:
V = I^2 x R (why is this equation used)
- all the power equations
- How to calculate uncertainty
That equation isn't correct, but here's a discussion (now locked) of how you can combine Ohm's law and the electrical power equation in various ways for various purposes:

I meant power sorry
No prob - just have a look at the link, se if it gives you what you need snd let us know if you have any follow-ups.

I'm sitting in my car waiting for my twins to finish their GCSE physics exam so this is a bit late but...

First think about _where_ the power is being dissipated.

If we are talking about the power dissipated in a resistor then I and V refer to the current and voltage through and across the resistor.

If you are talking about the power delivered by a battery then I and V apply to the battery.

In some cases you only know one variable (I or V) so you can use..

P=IV
And ohm's law
V=IR

To make either...

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

Then which you use depends on which variable you know.

One of my son's has just called to say the exam was "ok but challenging". How did you find it?