Why Does Current Flow When a Capacitor Is Connected by Wires?

In summary, there are no electric fields outside of a charged capacitor as they are canceled out due to superposition. However, a flow of current can still occur when a cable is connected to both ends of the capacitor, as the plates are connected and the capacitor can be discharged. The construction of a capacitor with metal and dielectric layers also means that one of the layers will be on the outside and can have a field around it when charged. It is also possible for the leads of a capacitor to have a voltage between them, as seen in microwave ovens.
  • #1
unseensoul
47
0
There are no electric fields outside of a charged capacitor as they are canceled out due to superposition, right?! So why is there a flow of current when a cable is connected to both ends of the capacitor?

I was told that there might be an E field in the wires. How come? Where does it come from?
 
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  • #2
A charged capacitor can be discharged by connecting the plates together.
That is what you do when you connect the two ends of a charged capacitor by a piece of wire.

A capacitor is made by making layers of metal and dielectric in a spiral on a central rod.
This means that one of the layers of metal must be on the outside of the capacitor. ie they can't both be on top.
So, this plate of the capacitor would certainly have a field around it if the capacitor was charged.
Maybe your first assertion isn't correct for normal capacitors?

Not sure what you mean by an "E" field. The leads of a capacitor can certainly have a voltage between them. There is a capacitor in all microwave ovens that is very capable of killing you.
 
  • #3


While it is true that, in an ideal scenario, there should be no electric fields outside of a charged capacitor due to superposition, in reality, there can be some residual electric fields present. This can be due to imperfections in the capacitor itself or external factors such as nearby objects or stray charges. These residual fields can also be affected by the material and design of the wires connecting the capacitor, resulting in a small but non-zero electric field in the wires.

When a cable is connected to both ends of the capacitor, there is a flow of current because the capacitor is essentially acting as a source of electric potential difference. This potential difference creates an electric field within the capacitor that pushes charges through the wires, resulting in a flow of current. Additionally, the residual electric fields mentioned earlier can also contribute to the flow of current.

So, while the ideal scenario may suggest no electric fields outside of a charged capacitor, in reality, there can be some present due to imperfections and external factors. These fields, along with the electric field created by the potential difference in the capacitor, contribute to the flow of current in the connected wires.
 

FAQ: Why Does Current Flow When a Capacitor Is Connected by Wires?

What is a capacitor and how does it work?

A capacitor is an electrical component that stores energy in the form of an electric field. It consists of two conductive plates separated by an insulating material, known as a dielectric. When a voltage is applied to the capacitor, it charges by storing positive and negative charges on the plates. The capacitor can then release this stored energy when needed.

What is the role of an electric field in a capacitor?

The electric field is the driving force behind the functioning of a capacitor. When a voltage is applied, the electric field between the two plates of the capacitor causes the electrons to accumulate on one plate and the positive charges on the other plate. This creates a potential difference between the plates, allowing the capacitor to store energy.

How are capacitors used in electronic circuits?

Capacitors have a wide range of applications in electronic circuits. They can be used for filtering, smoothing, and regulating voltage signals. They are also commonly used in timing circuits, signal coupling, and energy storage in power supplies.

What factors affect the capacitance of a capacitor?

The capacitance of a capacitor is affected by the surface area of the plates, the distance between the plates, and the type of dielectric material used. A larger surface area and a smaller distance between the plates result in a higher capacitance. Different types of dielectric materials have different permittivity values, which also affect the capacitance.

How do capacitors store and release energy?

Capacitors store energy in the form of an electric field between their plates. When a voltage is applied, the capacitor charges by storing positive and negative charges on the plates. When the capacitor is connected to a circuit, it can release this stored energy in the form of an electric current. The amount of energy stored in a capacitor is directly proportional to its capacitance and the square of the voltage applied.

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