How Can the Value of Capacitance Be Decreased?
Capacitance is the ability of a capacitor to store an electrical charge. The value of capacitance (CC) is determined by the physical characteristics of the capacitor, including the surface area of the plates, the distance between the plates, and the dielectric material used between the plates. Capacitance is inversely proportional to the distance between the plates and directly proportional to the surface area of the plates and the permittivity of the dielectric material.
To decrease the value of capacitance, several factors can be modified. Below are the primary ways to reduce the capacitance in a capacitor:
1. Decrease the Surface Area of the Plates
Capacitance is directly proportional to the surface area (AA) of the conducting plates of the capacitor. The formula for the capacitance of a parallel plate capacitor is: C=ϵ0⋅ϵr⋅AdC = \frac{\epsilon_0 \cdot \epsilon_r \cdot A}{d}
Where:
- CC is the capacitance,
- ϵ0\epsilon_0 is the permittivity of free space,
- ϵr\epsilon_r is the relative permittivity (dielectric constant),
- AA is the surface area of the plates,
- dd is the distance between the plates.
Thus, by reducing the surface area of the plates, the capacitance will decrease.
Example:
If you cut down the area of the plates (e.g., by making the plates smaller), the capacitance will decrease.
2. Increase the Distance Between the Plates
Capacitance is inversely proportional to the distance (dd) between the plates. The greater the distance between the plates, the lower the capacitance. If the plates are moved further apart, the ability of the capacitor to store charge will decrease, thus reducing the capacitance.
- Formula: C=ϵ0⋅ϵr⋅AdC = \frac{\epsilon_0 \cdot \epsilon_r \cdot A}{d}
- As dd increases, CC decreases.
Example:
Inserting a spacer or adjusting the physical distance between the plates can reduce the capacitance.
3. Use a Dielectric Material with Lower Permittivity
The dielectric material between the plates of a capacitor affects its capacitance. The dielectric constant (ϵr\epsilon_r) of the material is a measure of how much the material can increase the capacitance compared to air (which has a dielectric constant of 1). To reduce capacitance, you can use a dielectric material with a lower relative permittivity.
- Formula: C=ϵ0⋅ϵr⋅AdC = \frac{\epsilon_0 \cdot \epsilon_r \cdot A}{d}
- If the value of ϵr\epsilon_r is reduced, the capacitance will decrease.
Example:
Using a material with a lower permittivity, such as air or certain types of plastic, instead of materials with higher permittivity like ceramic or glass, will decrease the capacitance.
4. Use a Smaller Capacitance Value in Parallel Capacitors
When capacitors are connected in parallel, the total capacitance increases. To decrease the overall capacitance, you can use capacitors in a series configuration. When capacitors are connected in series, the total capacitance is given by the formula: 1Ctotal=1C1+1C2+1C3+…\frac{1}{C_{\text{total}}} = \frac{1}{C_1} + \frac{1}{C_2} + \frac{1}{C_3} + \dots
In a series arrangement, the total capacitance is always less than the smallest individual capacitance, thereby decreasing the overall capacitance.
Example:
If you have several capacitors with different capacitance values, connecting them in series will result in a lower total capacitance.
5. Reduce the Temperature
Capacitance can also be affected by temperature, depending on the dielectric material used. For most materials, as the temperature increases, the permittivity of the dielectric decreases, which reduces the capacitance. By lowering the temperature, the permittivity of the dielectric may increase, potentially increasing the capacitance, but for certain materials, reducing the temperature can lead to a decrease in capacitance.
Example:
If you’re using a material whose permittivity decreases with temperature, cooling the system might reduce the capacitance.
Conclusion
To decrease the value of capacitance, you can:
- Reduce the surface area of the plates.
- Increase the distance between the plates.
- Use a dielectric material with a lower permittivity.
- Connect capacitors in series to reduce the overall capacitance.
- Lower the temperature, depending on the dielectric material used.
Each of these methods modifies the physical or electrical characteristics of the capacitor, resulting in a decrease in its ability to store charge (capacitance).
