# Parllel Plate Capcitor separation distance and voltage

• rpardo
In summary, the conversation discusses a problem involving a PP air capacitor with two plates, a specific area and distance apart, and connected to a 12V battery. The goal is to find the capacitance, charge on each plate, electric field, and energy stored in the capacitor. When repeating the problem with the plates pulled apart to a greater distance, the capacitance halves but the charge on the plates stays the same. The conversation suggests reworking the equations and considering work to solve the problem.
rpardo
Hello,

I'm studying for an exam tomorrow and am facing a question I can't for the life of me fathom.

" A PP air capacitor is made by using to plates 16 cm squared, spaced 4.7 mm apart, connected to a 12V battery"

Find Capacitance, charge on each plate, electric field between plated, energy stored in the capacitor. If the battery is disconnected and then the plated pulled apart to a separation of 9.4 mm repeat answers.

I have no problem solving the first round of questions but when repeating with the new distance as expected capacitance halves.

using C=Q/V i try and figure out Q (Q=CV)
mathematically i expect Q to halve since Capacitance has also halved
physically i know there's been no change in charge
Since it is connected to a battery i can't justify in my mind the voltage increasing to 24V in order to harmonize my physical answer and my mathematical answer...
I think I am making mountains out of mole hills... i guess exam season will sometimes throw logic out the window.

If you disconnect the battery and keep the parallel plates unconnected, then the one thing you can be certain is that the charge on the plates stay the same. This is because there is no longer any circuit path for charge to migrate between the plates (unless the dielectric between the plates breaksdown but that is not a situation we usually consider and certainly won't happen here since separating the plates a larger distance can only decrease the electric field).

So rework your equations under assumptions that you know the area, distance of separation, and charge on the plates.

Note that pulling apart the plates adds energy since they are oppositely charged and attract each other. Considering work helps solve many physics problems.

## 1. What is a parallel plate capacitor?

A parallel plate capacitor is a device used to store electrical energy. It consists of two parallel conducting plates separated by a small distance and connected to a power source. When a voltage is applied to the plates, an electric field is created between them, allowing for the storage of electrical charge.

## 2. How does the separation distance between the plates affect the voltage of a parallel plate capacitor?

The separation distance between the plates is directly proportional to the voltage of a parallel plate capacitor. This means that as the distance between the plates increases, the voltage decreases and vice versa. This relationship is described by the equation V = Ed, where V is the voltage, E is the electric field, and d is the separation distance.

## 3. What is the ideal separation distance for a parallel plate capacitor?

The ideal separation distance for a parallel plate capacitor depends on the specific application and desired voltage. In general, a smaller separation distance between the plates allows for a higher voltage and a larger separation distance allows for a lower voltage. However, too small of a distance may cause the plates to touch and create a short circuit, while too large of a distance may result in a weaker electric field and a lower capacitance.

## 4. How does the material of the plates affect the separation distance and voltage of a parallel plate capacitor?

The material of the plates does not directly affect the separation distance and voltage of a parallel plate capacitor. However, different materials can have different dielectric constants, which affect the capacitance of the capacitor. A higher dielectric constant allows for a larger capacitance and therefore a higher voltage for the same separation distance.

## 5. Can the separation distance and voltage of a parallel plate capacitor be changed after it has been constructed?

Yes, the separation distance and voltage of a parallel plate capacitor can be changed after it has been constructed by adjusting the distance between the plates or by changing the voltage applied to the plates. However, these changes may require disassembling and reassembling the capacitor. Additionally, altering the separation distance and voltage may affect the overall performance and capacitance of the capacitor.

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