Dielectric effect on voltage

In summary, adding a dielectric between plates increases the capacitance, allowing for the storage of a greater quantity of charge. This does not necessarily require a decrease in voltage, as the voltage source can remain constant. The ground is considered a good conductor due to its large cross sectional area. The presence of a dielectric affects energy and voltage through the phenomenon of polarization, causing changes in voltage, capacitance, energy, and total fields. Charge remains unchanged when a dielectric is inserted between charged parallel plate capacitors due to the induction of dipole moments and their associated fields.
  • #1
mpswee2
6
0
1) When we insert dielectric between plates, plates can "hold" a greater quantity of charge since capacitance is increased.

But when capacitance increases, does it require that voltage decreases? (From the formula C = Q/V, capacitance and charge could increase while voltage remains constant.)

But voltage V = PE/Q. If Q increases due to greater capacitance, then voltage would have to decrease. But in a given circuit, if the voltage source remains the same before and after inserting the dielectric, I don't understand how the voltage could change.

2) Also, why is the "ground," as a generality, considered less resistant than other materials. How are we sure of this? For instance, when using a defibrillator, administrators need to elevate the patient off the ground lest the current "skip" the patients' heart. But why is the ground's resistivity invariably so low compared to human body's, building materials of a house?

Thanks for helping to clarify.
 
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  • #2
1, Correct, adding a dielectric allows you to either a, store the same charge with lower voltage or b, store a greater charge with the same voltage. Snce in proactice the voltage is usually a fixed part of the design a dielectric allows you to store more charge in a smaller space.
If the capacitor is no longer connected to the supply when you insert the dielectric then as the charge cannot change ( charge is conserved) the voltage will drop. If it is still connected to the supply then more charge will flow into the capacitor.

2, The ground is a good conductor because it's cross sectional area is rather large.
 
  • #3
1. What is the relationship between dielectric and
a. Energy
b. Voltage
as in how the prescence of a dielectric affects the Energy and voltage?? (increases, decreases etc) and please explain

2. Why is it that when a parallel plate capacitor is charged and then a dielectric slab is introduced btween it. Voltage, Capacitance and Energy change but charge remains unchanged?
 
  • #4
ram456 said:
1. What is the relationship between dielectric and
a. Energy
b. Voltage
as in how the prescence of a dielectric affects the Energy and voltage?? (increases, decreases etc) and please explain

2. Why is it that when a parallel plate capacitor is charged and then a dielectric slab is introduced btween it. Voltage, Capacitance and Energy change but charge remains unchanged?

All of this is associated with the phenomenon of polarization in a dielectric. An applied electric field across a dielectric induces dipole moments in the dielectric's molecules. That is, charge separation occurs because the Lorentz force on positive and negative charges act in opposite directions. These dipole moments also create their own secondary fields. The effects of these dipole moments and their associated fields are the cause for the changes in voltage, capacitance, energy and total fields. You can find more about these by looking in any undergraduate electrodynamics text like Griffiths.
 
  • #5


I would like to address the questions you have raised regarding the dielectric effect on voltage.

1) It is correct that when a dielectric is inserted between plates, the capacitance increases, allowing the plates to hold a greater quantity of charge. However, this does not necessarily mean that the voltage decreases. As you mentioned, according to the formula C = Q/V, if capacitance and charge increase while voltage remains constant, then the voltage would not change. This is because the voltage is dependent on both the charge and the capacitance, and if one increases while the other remains constant, the voltage will also remain constant.

In a given circuit, if the voltage source remains the same before and after inserting the dielectric, the voltage would not change. This is because the voltage source is the source of energy that maintains the voltage across the plates, and it would continue to do so regardless of the presence of a dielectric.

2) The "ground" is considered less resistant than other materials because it is typically a good conductor of electricity. This is because the ground is usually made up of materials such as soil, water, and metals, which contain free electrons that can easily flow and conduct electricity. In contrast, materials such as human bodies and building materials have higher resistance to the flow of electricity, meaning they do not allow the free flow of electrons.

In the case of using a defibrillator, the reason for elevating the patient off the ground is to ensure that the electric current flows through the patient's body, rather than being diverted through the ground. This is because the ground has a lower resistance compared to the human body, and the electric current would prefer to flow through the ground, rather than through the patient's body. This is why it is important to insulate the patient from the ground in such situations.

I hope this helps to clarify your questions about the dielectric effect on voltage and the resistance of the ground compared to other materials. If you have any further questions, please feel free to ask.
 

1. What is the dielectric effect on voltage?

The dielectric effect on voltage refers to the change in voltage that occurs when an insulating material, known as a dielectric, is placed between two conductors. This change in voltage is due to the polarization of the dielectric material, which reduces the electric field and thus alters the voltage.

2. How does the dielectric constant affect voltage?

The dielectric constant, also known as the relative permittivity, is a measure of a material's ability to store electric charge. A higher dielectric constant means that the material can store more charge, which decreases the electric field and increases the voltage. Therefore, a higher dielectric constant leads to a greater dielectric effect on voltage.

3. What is the difference between a dielectric and a conductor?

A dielectric is an insulating material that does not allow the flow of electric current, while a conductor is a material that allows the flow of electric current. The presence of a dielectric between two conductors will affect the voltage, while the presence of a conductor will not.

4. How does the distance between conductors affect the dielectric effect on voltage?

The distance between conductors, also known as the thickness of the dielectric material, has a direct impact on the dielectric effect on voltage. As the distance increases, the electric field decreases, resulting in a higher voltage. This relationship is known as the inverse square law, where the voltage is inversely proportional to the distance squared.

5. Can the dielectric effect on voltage be used in practical applications?

Yes, the dielectric effect on voltage has many practical applications. One example is in capacitors, where the dielectric material is used to increase the capacitance and store more charge. It is also utilized in high voltage power transmission, as the presence of dielectric materials in insulators reduces the voltage and prevents electrical breakdown.

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