# Question based on a video (battery and voltage)

1. Feb 9, 2016

### gracy

in all three cases there is no battery or voltage source,right?Because I can't see any battery.But there is voltage ,then without battery how is potential difference created?I think potential difference is generated due to charged capacitors not by battery or any other voltage source.

2. Feb 9, 2016

### cnh1995

Yes.In the circuit, the p.d. is due to the voltage across the charged capacitor. But for charging the capacitor before connecting it in the circuit, a battery might have been used.

Last edited: Feb 9, 2016
3. Feb 9, 2016

### gracy

In all three cases?

4. Feb 9, 2016

yes.

5. Feb 9, 2016

### gracy

Thanks @cnh1995

6. Feb 9, 2016

### cnh1995

You're welcome!

7. Feb 9, 2016

### gracy

In the above video for case 1 $V_f$ was potential across equivalent capacitance of $C_1$ and $C_2$ why he used the same $V_f$ for individual capacitors also?If there would have been any battery present like this

then in this case I understand how potential difference across $Ceq$ and individual capacitors is same.But we know it does not have any battery then how potential across equivalent capacitance of $C_1$ and $C_2$ and individual capacitors is same?

8. Feb 9, 2016

### cnh1995

The current will stop only when the voltages of C1 and C2 will be equal. Also, equivalent capacitane is connected between same two points as are C1 and C2.

9. Feb 9, 2016

### gracy

Is potential difference across equivalent capacitor always same as potential difference across it's individual component capacitors?

10. Feb 9, 2016

### cnh1995

For parallel capacitors, yes.

11. Feb 9, 2016

### gracy

Even when the potential difference is not due to /created by battery?

12. Feb 9, 2016

### sophiecentaur

Really , Gracy; you expect us to trawl through 8+ minutes of that really boring presentation, which you found confusing. Couldn't you just be kind to us and ask the actual question that the video raised in your mind? The Web is full of that sort of badly presented stuff that, presumably, some poor students are expected to get their education from. From your past posts, I can see you are not clueless and that you have a fair grasp of this subject. I am not just being grumpy when I ask you to ask specific questions in your own words. As my hero Old Jim often remarks, "a question well asked, is half answered". He's sooooo right. This stuff is well within your capabilities, I'm sure.

13. Feb 9, 2016

### cnh1995

Yes. Because there is no current in the circuit once the capacitors reach steady state. Current ceases to flow only when the capacitors have equal voltage.

14. Feb 9, 2016

### cnh1995

True! And Jim is one of the best science advisors I have known here on PF!

15. Feb 9, 2016

### gracy

Well ,I find that video both interesting as well as useful and I am not poor.To each his own.

I wonder how you found out that it is for poor students.It is for educational purpose and we should not classify it as you did .Education is same for all poor or rich.

16. Feb 9, 2016

### jbriggs444

In the vernacular, the "poor whoever" phrase does not indicate that the person is poor financially, but that the situation being described is one which does not act to his or her benefit.

e.g. "oh, those poor people in the oncoming lanes of traffic heading toward that backup that we just passed" applies equally well when those poor people are driving rusted out beaters or new model BMW's.

17. Feb 9, 2016

### gracy

Obviously I know that.

But the way he has written ,it looks like he did mean poor( financially).

18. Feb 9, 2016

### sophiecentaur

I am so sorry it came across that way. I meant 'poor' in the sense that the students would have been suffering with such a boring presentation.
Our common English language is full of pitfalls.

19. Feb 9, 2016

### cnh1995

Well, I liked that post because of its last few lines and Jim's quote. But I disagree with what you said in the first part. Maybe you find his Indian accent boring but I don't think all the students are getting bored with such presentations. You are an old, experienced man. You might have gone through a different learning environment and hence, you might be finding these videos boring, but that doesn't mean all the students should find them boring. "Boring" and "bad presentation" are your personal opinions but with all due respect, I do not think you should express them that way. Some videos like that have been very helpful for me and many of my fellow students. So, I personally think that remark is somewhat rude.

20. Feb 9, 2016

### jbriggs444

It may have been obvious to you. You may have expected it to be obvious to others. However, if it was obvious to me, I would not have attempted an explanation.

It is often useful when interacting over the Internet to assume good intent -- to grow a thick skin and allow imagined slights, insults or misrepresentations to go unchallenged.