Dielectric Meaning
Dielectric is a material that possesses insulating properties. It is a substance that has the ability to transmit electric force without conduction.
We see many kinds of electric and polarized materials that have some sort of combined property. As you go through this article, you will come across many terms related to dielectric and its applications in today’s life situations. You will also get to know unitless values and numbers that describe the behavior of electric insulators when kept under the influence of an electric field. So, let’s hop down!
What is Dielectric?
In the above text, we understood how to define dielectric, i.e., a dielectric aka dielectric material is an electrical insulator. When it is subjected to the external electric field, it gets polarized. Also, they are very poor conductors of electricity.
Now, let us define the dielectric constant:
The dielectric constant is the ratio of the Permittivity of a substance to the Permittivity of free space. Further, it is expressed as the extent to which any element gets intensified by the electric flux. This becomes the electrical equivalent of relative magnetic permeability.
Now, what is dielectric material? A dielectric particle is an insulator.
So, what is the dielectric definition?
Point to Note:
Electric charges don’t flow through the materials as they react when subjected to an electrical conductor; however, they shift from their position and value that leads to dielectric polarization. Since the material is polarized, the positive charges get displaced towards the field, and negative charges go away from the field.
For instance, if the field moves in the x-axis, the negative charges get directed towards the negative x-axis. This, in turn, builds an internal electric field that minimizes the overall area inside the dielectric. In case the dielectric has weak bond molecules, they will not only get polarized but also become re-oriented letting the symmetric axes to be aligned with respect to the field.
Concept of Dielectric Constant
With the rise of the dielectric constant, there is also a sharp rise in electric flux density. However, the remaining factors don’t change. This lets the element of any material size like metal plates maintain the electric charge for a lengthy time span, thereby holding a considerable amount of charge. Besides, substances that possess high dielectric constants are applied to be used in creating highly valued capacitors.
You cannot desire any high dielectric constant through its own properties. Honestly speaking, these substances will break down more naturally when it is under the subjection of a high electric field. This is unlike the case with materials having a low dielectric constant.
For instance, dry air possesses a low dielectric constant; however, this is the best example of dielectric materials for capacitors. As such, it has considerably been used in high-power radio frequency transmitters. In case the air inside comes across any dielectric breakdown, still, the consequence is not fatal and is temporary. If the excess electric field is taken out, the air gets back to its normal state. There are also certain solid dielectric substances like glass and polyethylene that can endure permanent damage.
What is the Dielectric Material?
We know that the dielectric constant is the ratio of the capacitance induced by two metallic plates in presence of an insulator, to the capacitance of the same place with vacuum or air.
When a material is used for any insulation application, there is a need to have a low dielectric constant.
The formula for dielectric constant goes as:
\[k=\frac{C\epsilon _0A}{d}\]and\[k=\frac{C_0}{C}\]
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Here:
C = capacitance used in material as the dielectric-capacitor
C0 = capacitance when the vacuum is used as dielectric
T = Thickness of the sample
A = Area of the plate
ε0 = Permittivity of free space (8.85 x 10⁻¹² F/m, i.e., Farad per meter)
Application of Dielectric Constant
This electrical property phenomenon is a dimensionless measurement. The standard tests to measure dielectric plastics are ICE 60250, ASTM D150, and a few more methods.
These methods comprise:
At first, a sample is placed between the 2 metal plates. Here, the value of capacitance is taken. Then, again the value is measured without the specimen between the two electrodes. The dielectric constant is nothing but just the value of their ratios.
Here, the test can be applied at a range of frequency values, actually within the 10Hz and 2 MHz range.
The sample here should be larger and flat than the 50 mm circular electrode.
A dielectric material is used to split the conductive plates of a capacitor. This insulating material considerably determines the properties of a component. The dielectric consistent of a material determines the amount of electricity that a capacitor can store whilst voltage is applied.
A dielectric material becomes polarized whilst it is exposed to an electric field. When polarization occurs, the powerful electric area is reduced. Since the permittivity of a material is depending on frequency and temperature, the dielectric consistent is generally given at precise conditions, generally at low frequencies. Moreover, the dielectric consistent of a material is usually given relative to the permittivity of free space.
FAQs on Dielectric
1. What is a dielectric in simple terms as per the CBSE Class 12 Physics syllabus?
In simple terms, a dielectric is an electrical insulator that can be polarised by an applied electric field. Unlike a conductor, which allows electric charges to flow freely, a dielectric does not. Instead, the charges within the dielectric material shift slightly from their average equilibrium positions, creating internal dipoles. This property makes them essential components in devices like capacitors.
2. What are some common examples of dielectric materials?
Dielectric materials are very common and are used in numerous applications. Some typical examples include:
- Glass: Used as an insulator in various electrical components.
- Mica: Known for its excellent dielectric strength and stability, often used in high-voltage capacitors.
- Paper: Specially treated paper is used in many types of capacitors.
- Plastics: Materials like Teflon, Mylar, and Polystyrene are widely used as dielectrics.
- Distilled Water: Pure water is a good dielectric, although impurities make tap water conductive.
- Air: Is the most basic dielectric medium used in simple parallel plate capacitors.
3. What is the main function of a dielectric slab when placed inside a capacitor?
The primary function of inserting a dielectric slab into a capacitor is to increase its capacitance. When the dielectric is placed between the capacitor plates, it becomes polarised, creating an internal electric field that opposes the external field. This reduces the net electric field and, consequently, the potential difference between the plates for the same amount of charge. Since capacitance (C) is defined as C = Q/V, a decrease in potential difference (V) results in an increase in capacitance.
4. How does a dielectric material actually increase the capacitance of a capacitor?
A dielectric increases capacitance through a process called polarisation. When an external electric field (E₀) is applied across the dielectric, its molecules form dipoles that align themselves to create an internal electric field (Eᵢ) in the opposite direction. This opposing field reduces the net electric field between the plates (E = E₀ - Eᵢ). According to the relationship V = Ed, a lower electric field (E) for a fixed distance (d) results in a lower potential difference (V) across the plates. Since capacitance is C = Q/V, storing the same charge (Q) at a lower potential difference (V) means the capacitance has significantly increased.
5. What is the difference between polar and non-polar dielectrics?
The main difference between polar and non-polar dielectrics lies in their molecular structure:
- Polar Dielectrics: These materials have molecules where the centre of positive charge and the centre of negative charge do not coincide, even without an external electric field. They possess a permanent dipole moment. Examples include H₂O and HCl.
- Non-Polar Dielectrics: In these materials, the centre of positive charge and the centre of negative charge coincide. They do not have a permanent dipole moment. A dipole moment is only induced when an external electric field is applied, which stretches the molecules. Examples include O₂, N₂, and H₂.
6. How is the dielectric constant (K) of a material defined and calculated?
The dielectric constant (K), also known as relative permittivity (εᵣ), is a dimensionless factor that indicates how much a dielectric material can increase capacitance. It can be defined in two primary ways:
- It is the ratio of the capacitance of a capacitor with the dielectric medium (C) to the capacitance of the same capacitor with a vacuum or air as the medium (C₀). Formula: K = C / C₀.
- It is also the ratio of the permittivity of the substance (ε) to the permittivity of free space (ε₀). Formula: K = ε / ε₀.
A higher value of K means the material is more effective at storing energy in a capacitor.
7. What is the difference between dielectric constant and dielectric strength?
Students often confuse these two terms, but they describe very different properties:
- Dielectric Constant (K): This is a measure of a material's ability to store electrical energy when placed in an electric field. It is a multiplier that tells you how much the capacitance increases compared to a vacuum.
- Dielectric Strength: This refers to the maximum electric field a dielectric can withstand without breaking down and becoming conductive. If the field exceeds this value, the material's insulating properties fail, leading to a spark or short circuit. It is a measure of the material's voltage endurance.
In short, the dielectric constant relates to storage capacity, while dielectric strength relates to safety and operational limits.
8. What happens if the voltage across a capacitor exceeds the dielectric's breakdown strength?
If the voltage applied across a capacitor becomes so large that the electric field exceeds the dielectric's strength, a phenomenon called dielectric breakdown occurs. At this point, the insulating material can no longer withstand the field and it becomes a conductor. A large current flows through the dielectric, often in the form of a spark, which permanently damages the capacitor. This is why capacitors have a maximum voltage rating that should not be exceeded.
