Two capacitors connected in series

  • Thread starter Thread starter songoku
  • Start date Start date
  • Tags Tags
    Capacitors Series
Click For Summary

Homework Help Overview

The problem involves two capacitors with capacitances of 30 μF and 60 μF, each initially having charges of 50 μC and 70 μC, respectively. The capacitors are then connected in series, and the task is to determine the potential difference across each capacitor after the connection.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the implications of connecting capacitors in series, noting that charge should be the same across each capacitor in such a configuration. There is confusion regarding the initial charges stated and whether they are capacitance values or actual charges. Questions arise about how current can flow when only one plate of each capacitor is connected together.

Discussion Status

The discussion is ongoing, with participants exploring the correct interpretation of the problem and the implications of the series connection. Some guidance has been provided regarding the nature of current flow in the circuit, but there is no explicit consensus on the correct approach or outcome.

Contextual Notes

There is a noted confusion regarding the units used for charge and capacitance, which may affect the understanding of the problem. Additionally, the original poster mentions multiple choice answers, raising questions about the validity of those options based on the discussion.

songoku
Messages
2,514
Reaction score
395

Homework Statement


Two capacitors, capacitance of 30 μF and 60 μF respectively, each has charge of 50 μF and 70 μF. The capacitors then connected in series. Find the potential difference on each capacitor now


Homework Equations


Q = CV


The Attempt at a Solution


I know that the charge should be same for series circuit but I don't know how to analyse this question. Each capacitors has its own charge and voltage and after connected in series, their charge should be the same. How to find it?
 
Physics news on Phys.org
songoku said:
... each has charge of 50 μF and 70 μF?

uF is a measure of capacitance, not charge, so I don't understand what you are saying here.
 
Think about what "The capacitors then connected in series" means. Presumably only one plate of each is connected together otherwise they would be in parallel. If only one side of each capacitor is connected together how much current can flow?
 
phinds said:
uF is a measure of capacitance, not charge, so I don't understand what you are saying here.

sorry, I meant 50 μC and 70 μC

CWatters said:
Think about what "The capacitors then connected in series" means. Presumably only one plate of each is connected together otherwise they would be in parallel. If only one side of each capacitor is connected together how much current can flow?

Sorry I really don't know the concept here of how to determine the current when only one side of each capacitor is connected...I assume that one positive plate is connected to other negative plate. Will the case be the same if the series circuit connects positive plate to positive plate?

Thanks
 
If the only one end of each capacitor is connected to anything there is no closed circuit so no current flow. Therefore the capacitors retain whatever charge and voltage they had before they were connected.
 
CWatters said:
If the only one end of each capacitor is connected to anything there is no closed circuit so no current flow. Therefore the capacitors retain whatever charge and voltage they had before they were connected.

Sorry, actually there are choices for this question:
a. 4 and 8 Volt
b. 8 and 4 Volt
c. 5 and 5 Volt
d. 3 and 6 Volt
e. 6 and 3 Volt

If the capacitors retain their voltage, their voltage should be 5/3 and 7/6 Volt.

So there is no correct choice?

Thanks
 

Similar threads

Replies
20
Views
2K
  • · Replies 4 ·
Replies
4
Views
6K
  • · Replies 4 ·
Replies
4
Views
4K
Replies
4
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
Replies
5
Views
1K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 18 ·
Replies
18
Views
3K