25.7
Condensator Met Een Diëlektricum
Parallelle plaatcondensatoren bestaan uit twee geleidende platen die op een bepaalde afstand van elkaar zijn gescheiden. Het is echter mechanisch moei…
Parallel plate capacitors consist of two conducting plates separated by a small distance. However, it is mechanically difficult to hold the plates closer without any contact. This can be resolved by placing a non-conducting medium sandwiched between the capacitor plates.
Most commonly, capacitors are made of long strips of metal foils separated by a dielectric medium. Dielectrics are non-conducting materials with no loosely bound or free electrons.
Consider a fully charged parallel plate capacitor with a dielectric slab filling the gap between the plates. The dipoles in the dielectric align along the direction of the electric field.
The alignment of the negative charges toward the positive plate and the positive charges toward the negative plate reduces the voltage across the plates, although the total charge remains the same. The decrease in voltage increases the capacitance.
The factor by which the capacitance increases is the material's dielectric constant. The presence of a dielectric always increases the capacitance. Hence, the dielectric constant is always greater than unity.
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Q1: Why is a dielectric material placed between capacitor plates?
A dielectric is placed between capacitor plates to solve the mechanical difficulty of holding large parallel plates without contact. The dielectric layer maintains a small gap between the plates while increasing capacitance. Dielectrics are non-conducting materials with no free or loosely bound electrons, making them ideal for this purpose.
Q2: How does a dielectric affect the voltage and charge in a capacitor?
When a dielectric fills the gap between capacitor plates, its dipoles align along the electric field direction. This alignment reduces the voltage across the plates by orienting negative charges toward the positive plate and positive charges toward the negative plate. However, the total charge on the plates remains conserved despite the voltage decrease.
Q3: What is the dielectric constant and why is it always greater than one?
The dielectric constant is the factor by which capacitance increases when a dielectric is introduced between the plates. Since the presence of a dielectric always increases capacitance, the dielectric constant is always greater than unity. It quantifies how much a specific material enhances the capacitance compared to an empty capacitor.
Q4: How does a dielectric increase capacitance in a parallel plate capacitor?
A dielectric increases capacitance by reducing the voltage across the plates through dipole polarization. When dipoles align with the electric field, they create an opposing field that lowers the overall voltage. Since capacitance is inversely related to voltage for a fixed charge, the voltage reduction directly increases the capacitance value.
Q5: What happens to the electrical energy stored when a dielectric is added to a capacitor?
The electrical energy stored in a capacitor is reduced when a dielectric is introduced. If the initial energy stored is U0, the energy U with a dielectric is reduced by a factor of the dielectric constant. This reduction occurs because the dielectric lowers the voltage across the plates while charge remains constant.
Q6: What are the structural characteristics of dielectric materials?
Dielectric materials are non-conducting substances with no free or loosely bound electrons. In practical capacitor construction, long strips of metal foils are separated by a dielectric medium to create the capacitor structure. These materials allow dipoles to align with applied electric fields without conducting current.
Q7: How does dipole alignment in a dielectric reduce the electric field between capacitor plates?
When a dielectric is placed in an electric field, its dipoles align along the field direction. The negative charges orient toward the positive plate and positive charges toward the negative plate. This alignment creates an internal opposing field that reduces the net electric field and voltage between the plates.