00:01
So this question asks, how much charge does this 12 -volt battery need to have, if it wants to supply these and fully charged, these 2 .5 and 5 micro -fad capacitors if they're in parallel in series, and then how much energy in either case? so we have this 12 -volt battery.
00:22
And so let's find the equivalent capacitance in either case.
00:29
So we have c1 is 2 .5 micro -faird.
00:40
C2 is equal to 5 micro -faird.
00:49
And so the c -equivalent for, so let's do parallel first.
00:55
So parallel.
01:01
If they're in parallel, you just add them like normal.
01:04
So c equivalent is equal to 7.
01:09
0 .5, nope, not 7 .2, microfarad.
01:23
And in series, you want to do this inverse adding.
01:29
So 1 over c equivalent is equal to 1 over 5 plus 1 over 2 .5.
01:37
Solving for c equivalent gives us, i'm typing it into my calculator right now, 1 .67 microfarad.
02:06
So if we want to get the total charge, then for the parallel case, q is c equivalent.
02:14
So this is the charge coming from the battery times the voltage.
02:18
So it's going to be 12 times 7 .5, which is 90 microculomes.
02:30
And then in this case, the charge again is going to be the c equivalent times voltage.
02:35
So that's going to be 1 .67 times 12, which is 20 .0.
02:52
I'll just do 20 microcolones.
02:56
And what exactly does a question ask? okay, so that's the answer to a.
03:03
That's how much charge it has to supply.
03:05
And then how much energy does the battery have to supply in each case? so let me cordon this off.
03:17
So this is the answer for a.
03:22
For b, you just want to use u.
03:27
Actually, what is the potential energy? i always mix these up.
03:31
So potential energy capacitor.
03:35
It's like one half cv squared...