00:01
What we know is that the amount of the battery is 12 volts.
00:04
The battery has an internal resistance of 0 .4 oms.
00:09
And a resistor that's connected to this battery dissipates power at 80 watts.
00:17
And we want to know what two values of our will dissipate power at 80 watts.
00:25
So we know that power dissipated is.
00:31
The current times the voltage or the potential difference across the resistor and we also know that the potential difference is equal to the emf minus the drop across the internal resistance so we can substitute the second part into the first part so we have that the power is i times e minus i r.
01:23
Okay.
01:24
And we get that p is equal to i .e minus i squared r.
01:36
And i'm going to rearrange this in a different way so that it'll be more suggestive.
01:45
So if i have r -i squared minus e -i plus p equals 0, this should remind you of a quadratic equation, right? so we have something like a -x -quared plus b -x plus c, right? so we can write a quadratic.
02:08
A -x -squared plus b -x -c is equal to zero...