# Capacitors , why cant series combination be used in an open circuit?

1. Dec 30, 2013

### K Dhiraj Bhak

Capacitors , why cant series combination be used in an open circuit??

they say we cannot apply series combination formula for the capacitors in an open circuit,,,but why?? why cant we find the equivalent capacitance in an open circuit?

2. Dec 31, 2013

### davenn

what do you mean " in an open circuit "
show us a drawing of what you are referring to

cheers
Dave

3. Dec 31, 2013

### K Dhiraj Bhak

4. Dec 31, 2013

### CWatters

I refer you to the last part of this reply on that thread..

In short.. You can find the equivalent capacitance BUT you also need to find the correct equivalent charge.

Hint: You cannot just add the two charges together. If you do that the initial voltage will be wrong. The equivalent capacitance it 1.2uF. You calculated the charge to be 660μC so the initial voltage would be 660μC/1.2uF = 550V. That's wrong, it should be 100+180=280V according to the problem statement. Recalculate the correct charge.

Last edited: Dec 31, 2013