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**1. The problem: A resistor has a resistance R, and a battery has an internal resistance r. When the resistor is connected across the battery, ten percent less power is dissipated in R than would be dissipated if the battery had no internal resistance. Find the ratio r/R.**

**2. Homework Equations :**

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

V(IR)=emf - Ir

Obviously a series circuit when the battery's internal resistance and the resistor are both considered... so those relationships apply also

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

V(IR)=emf - Ir

Obviously a series circuit when the battery's internal resistance and the resistor are both considered... so those relationships apply also

## The Attempt at a Solution

I have been struggling with this one for awhile. I don't really know how to approach it. What I am having trouble understanding is how to choose which of the relationships describing power I need to use to solve the problem. There are three which could be relevant: P=IV, P=I^2R, P=V^2/R ... I am not sure which ones to use to

**set up my initial ratio**and thereby solve the problem.

So far I have these (where o is "naught..."), describing power in the no-current and current scenarios, respectively:

P(o) = IV(o)

P(1) = IV(o) - (I^2)r

But I am not sure to proceed...