Why does power increase by factor of 4 with four D-cells instead of 2?

[thisisfudd]

Hi,

I have a pretty straightforward problem that I am screwing up on for unknown reasons. Basically, it's about two D-cell 1.5-V babtteries connected in series. The give the current and you calculate the resistance and power -- simple enough. But then they ask by what factor would the power increase if four D-cells were connected (and why this would be dangerous). I have no clue. I figured given the relationship between power and voltage that it would be 2, but they say it's 4.

But P=IV!

 

[vincentchan]

if the resistance unchange, double the voltage will also double the current

 

[thisisfudd]

ohhhh i see. cool, thanks