Turn on thread page Beta
 You are Here: Home >< Physics

# Questions on Capacitors watch

1. Two questions about capacitors which I'm not sureo n how to solve

1)A capacitor with a capacitance of 1.77 x 10^-10 F is charged to 10 V. It is then disconnected from the power supply and the air gap is increased to 1mm. Determine the new potential across the plates.

(it is a parallel plate capacitor)

previous air gap was 0.5mm and ε0 = (8.85 x 10^-12 Fm^-1) and the area is 10cm x 10cm

2) In the circuit below, the switch is thrown upwards to the the 1 μF capacitor and is then thrown downwards. Determine the final potential difference between A and B.

(note I forgot to draw on A and B, these two points are on the bottom 2 corners of the circuit diagram, either side of the 5 μF capacitor)

2. (Original post by luke90)
2) In the circuit below, the switch is thrown upwards to the the 1 μF capacitor and is then thrown downwards. Determine the final potential difference between A and B.
The p.d. would be 10V. However, the charge wouldn't be stored evenly between the capacitors.

(Original post by luke90)
1)A capacitor with a capacitance of 1.77 x 10^-10 F is charged to 10 V. It is then disconnected from the power supply and the air gap is increased to 1mm. Determine the new potential across the plates.

(it is a parallel plate capacitor)

previous air gap was 0.5mm and ε0 = (8.85 x 10^-12 Fm^-1) and the area is 10cm x 10cm
Well I'm not sure about this one, but as the separation has doubled, the p.d. might have doubled (it would definately increase).
3. Starofale is wrong (sorry mate)

the 1st capacitor gats a certain amount of charge Q = C V

when the switch is closed this charge is shared between the two capacitors in such a way that the p.d. across each of them is the same.

so V = Q1 / C1 = Q2 / C2 so Q1/Q2 = C1/C2

the bigger capacitor therefore gets 5 times more charge

so it gets 5/6 of the original charge. Knowing this you can now do V = Q/C to find V

Turn on thread page Beta
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:
Updated: January 22, 2010
Today on TSR

### Are you living on a tight budget at uni?

From budgets to cutbacks...

### University open days

1. University of Cambridge
Wed, 26 Sep '18
2. Norwich University of the Arts
Fri, 28 Sep '18
3. Edge Hill University
Faculty of Health and Social Care Undergraduate
Sat, 29 Sep '18
Poll

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