- #1

Jimmy87

- 686

- 17

## Homework Statement

Question - Calculate the rate of energy transferred to the 1.5V cell during charging if the potential between X and Y is 1.9V

## Homework Equations

P = VI

## The Attempt at a Solution

I think I understand how to get the answer. If XY has 1.9V then the resistor will get 0.4V. This will give a current of 0.44A (0.4V/0.6Ω). Using P=VI for the cell, I get 0.44A x 1.5V = 0.6W. However, thinking about it more I have a few questions. I was thinking about why I couldn't use other circuit power equations - P = I

^{2}R and P = V

^{2}/R but then I realized this would give the power delivered to the internal resistor and not the cell. However, if we work backwards and use P = V

^{2}/R for the cell to find R then what does this mean? i.e. we know it has a power of 0.6W and a voltage of 1.5V so R = V

^{2}/P = 3.75Ω. Is this right or is it not valid to use it in this context?

Thanks for any help offered.