# What Happens to the Voltage Across a Capacitor When the Plates are Separated?

• gracy
In summary, the voltage across the capacitor increases when the plates are separated until they are twice as far apart as originally, despite the incorrect formula on page 10 of the provided PDF. The correct formula is ΔV = Q/C, not C/Q.
gracy
A capacitor has a capacitance C and is charged using a battery. After disconnecting the battery the two plates are separated until they are twice as far apart as originally. What happens to the voltage across the capacitor?
I think answer should be voltage increases . As battery has been disconnected q will remain same . Distance between the plates is increasing , capacitance should decrease.
##Q##= CΔV
As Q is constant and C is decreasing , V should increase.
But according to http://www.bama.ua.edu/~tmewes/PH-106/2008/clicker%20questions/CH26%20Clicker.pdf
Go to page 10
Voltage goes down . It is wrong . And formula is also wrong. Is that correct?

I have gone through all 14 pages of this pdf and found them right except this one , but I want to confirm are all other 13 pages correct?

Last edited by a moderator:
gracy said:
As Q is constant and C is decreasing , V should increase.
But according to http://www.bama.ua.edu/~tmewes/PH-106/2008/clicker%20questions/CH26%20Clicker.pdf
Go to page 10
Voltage goes down . It is wrong . And formula is also wrong. Is that correct?

I agree with you ... it may have been a genuine highlighting mistake ?it increases because you do work on the system to spread the plates, this results in an increase in potential energyDave

Last edited by a moderator:
gracy
gracy said:
I have gone through all 14 pages of this pdf and found them right except this one , but I want to confirm are all other 13 pages correct?

Yes, the formula is wrong on that page.(10)

gracy
gracy said:
A capacitor has a capacitance C and is charged using a battery. After disconnecting the battery the two plates are separated until they are twice as far apart as originally. What happens to the voltage across the capacitor?
I think answer should be voltage increases . As battery has been disconnected q will remain same . Distance between the plates is increasing , capacitance should decrease.
##Q= CΔV##
As Q is constant and C is decreasing , V should increase.
But according to http://www.bama.ua.edu/~tmewes/PH-106/2008/clicker%20questions/CH26%20Clicker.pdf
Go to page 10
Voltage goes down . It is wrong . And formula is also wrong. Is that correct?

I have gone through all 14 pages of this pdf and found them right except this one , but I want to confirm are all other 13 pages correct?
You are right.

Solving ##\ Q= C\,ΔV\ ## for ΔV gives ##\displaystyle\ \Delta V = \frac QC \ ##.

That pdf / PowerPoint has the incorrect ##\displaystyle\ \Delta V = \frac CQ \ ##.

Last edited by a moderator:

## What is capacitance?

Capacitance is the ability of a system to store an electric charge. It is measured in farads (F) and is dependent on the geometry and material properties of the system.

## How do I calculate capacitance?

Capacitance can be calculated by dividing the amount of charge stored (Q) by the potential difference (V) across the system: C = Q/V. It can also be calculated by considering the geometry and material properties of the system using the equation C = εA/d, where ε is the permittivity of the material, A is the area of the plates, and d is the distance between the plates.

## What is the purpose of a capacitance pdf crosscheck?

A capacitance pdf crosscheck is used to ensure the accuracy of measured capacitance values by comparing them to known reference values. This helps to identify any errors in the measurement process and improve the reliability of the results.

## How does a capacitance pdf crosscheck work?

A capacitance pdf crosscheck involves comparing the measured capacitance values to a known reference value using a test capacitor. The reference value is usually provided in a pdf file, and the capacitance values are compared using a multimeter or other measuring device.

## What are some common sources of error in capacitance measurements?

Some common sources of error in capacitance measurements include stray capacitance, temperature changes, and variations in the dielectric material. It is important to minimize these sources of error and use proper measurement techniques to obtain accurate results.

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