# B Electrical Power Loss Equations Confusion

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1. May 25, 2017

### Kevin Shen

Why is the equation Power Loss = I^2*R rather than Power Loss = V*I?
What I mean is why use I/R to represent V?
Also if Power Loss is equivalent to V*R, doesn't step up transformers which creating higher voltage also cause Power Loss to increase which contradicts to textbooks stating that power loss decreases if voltage rises given that power supply is same?

Last edited: May 25, 2017
2. May 25, 2017

### scottdave

You could use V*I or V^2/R to represent power (not V*R). But you need to understand how to use it. Look at a resistor. If the resistor has 50 ohms, and there is 10 volts across it, how do you find the power dissipated in the resistor? You can find the current in the resistor, then multiply current x voltage (across the resistor). If you look at Ohm's Law [V = I*R, not I/R], then you can substitute one of these values for it's equivalent combination of the other 2.

3. May 25, 2017

### Staff: Mentor

Power isn't V*R it is either V2/R or V*I. And V isn't I/R, it is I*R.

But in either case, as said above you can use different equations for different problems depending on what you need.

4. May 25, 2017

### Kevin Shen

Yeah I realized I made the error and I get it now :)