Homework Help: PHYSICS

Posted by nat on Monday, February 4, 2008 at 2:33am.

Two capacitors, C1=25.0x10^-6 and C2=5.0x10^-6 are connected in parallel and charged with a 100-V power supply.
a)calculate the total energy stored in the 2 capacitors
b) what potential difference would be required across the same 2 capacitors connected in series in order that the combination store the same energy as in a)?

ENERGY STORED=1/2C*DELTA V^2
1/2(25.0e^-6 + 5.0e^-6)(100)^2
=0.15KJ OR 150J, IS THIS RIGHT? IF NOT HOW DO I GET THE RIGHT ANSWER?

B)1/Ceq= 1/25.0e^-6 + 1/5.0e^-6= 4.16e^-6
DELTA V= SQRT 2x (ENERGY STORED=150J)/
4.16e^-6 = 8492v?????? CAN SOMEONE TELL ME IF IM DOING THIS RIGHT?

PHYSICS - drwls, Monday, February 4, 2008 at 2:47am
The stored energy that you calculate with that formula is in J, not kJ. The answer to the first part is 0.15 J

For the second part, require that
(1/2)Ceq*V^2 = 0.15 J, and solve for V. You are correct that Ceq = 4.167*10^-6 F
- PHYSICS - nat, Monday, February 4, 2008 at 3:24am
  so for part two i get 268V is that correct?
PHYSICS - drwls, Monday, February 4, 2008 at 6:59am
Yes

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