You are Here: Home >< Physics

# Capacitors' safe working voltage

1. I'm having problem with part (ii) of this question:

As the potential difference across two things in parallel is same, so the total safe working should be 12 V. 6V for the left hand side capacitor and 6V for the capacitors in parallel. But mark scheme says:
"p.d. across parallel combination = ½ ×p.d. across single capacitor
maximum is 9V"

Why is it dividing the potential difference by two for parallel capacitors? Like I said, isn't the potential difference same when two capacitors are in parallel?
2. The two in parallel have a total of 60uF and the other is 30uF
If you connect across this combination the ratio of the pd across the parallel to the pd across the single will be 30 / 60 (=1/2) because V= Q/C (V is inversely prop to capacitance)
So it must be 3V across the parallel pair and 6V across the single. This gives the maximum 6V across the single capacitor.
3. Hmm, things are rarely straightforward as they seem! Anyway, many thanks.
4. what if all the three have different values of both capacitance and breakdown voltage value.???????/
5. (Original post by nidhi dahiya)
what if all the three have different values of both capacitance and breakdown voltage value.???????/

but work out the voltage ratios based on the capacitance as shown by stonebridge

use the ratios to solve with algebra or by trial & error (if the overall voltage isn't limited by one of the parallel capacitors it must be the series capacitor)

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: January 29, 2015
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### Need help with revision?

Check out our study tools and resources now.

### My mum and BFF's mum are having an affair

Poll
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.