Chapter 3: Problem 31
Determine the capacitance of a parallel-plate capacitor having plates \(100 \mathrm{~mm}\) by \(0.3 \mathrm{~m}\) separated by \(0.04 \mathrm{~mm}\). The dielectric constant \(\epsilon=100 \mathrm{pF} / \mathrm{m}\).
Short Answer
Expert verified
The capacitance of the capacitor is 75,000 pF.
Step by step solution
01
Understanding the Problem
The capacitance of a parallel-plate capacitor is given by the formula:\[C = \epsilon \frac{A}{d}\]where \( C \) is the capacitance, \( \epsilon \) is the permittivity (dielectric constant), \( A \) is the area of the plates, and \( d \) is the separation between the plates. We need to calculate \( C \) given \( \epsilon = 100 \text{ pF/m} \), plate dimensions, and separation.
02
Calculate the Area of the Plates
First, convert the given plate dimensions into meters:- Length = 0.3 m- Width = 0.1 m (since 100 mm = 0.1 m)Calculate the area \( A \) of one plate:\[A = \text{Length} \times \text{Width} = 0.3 \times 0.1 = 0.03 \text{ m}^2\]
03
Convert Separation to Meters
Given the plate separation is 0.04 mm, convert this to meters:\[0.04 \text{ mm} = 0.04 \times 10^{-3} \text{ m} = 0.00004 \text{ m}\]This will be used directly in the calculation for capacitance.
04
Calculate the Capacitance
Now, substitute the values into the capacitance formula:\[C = \epsilon \frac{A}{d} = 100 \frac{\text{pF/m}}{1} \frac{0.03}{0.00004}\]This simplifies to:\[C = 100 \times \frac{0.03}{0.00004} = 100 \times 750 = 75000 \text{ pF}\]Thus, the capacitance is \( 75000 \text{ pF} \) (picoFarads).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Parallel-Plate Capacitor
A parallel-plate capacitor is a device that stores electrical energy by using two flat, conductive plates. These plates face each other and are separated by a small distance. Think of it as two thin pancakes stacked with a tiny air gap. This design allows for a simple and efficient way to store charge.
The electric field generated between the plates causes one plate to gain a positive charge and the other to fill with a negative charge. This separation is crucial, as this is where the energy is stored. By applying a voltage across the plates, it enhances the potential energy difference, thus storing more energy.
Key factors include:
The electric field generated between the plates causes one plate to gain a positive charge and the other to fill with a negative charge. This separation is crucial, as this is where the energy is stored. By applying a voltage across the plates, it enhances the potential energy difference, thus storing more energy.
Key factors include:
- Plate Area: Larger plate areas can store more charge. A bigger pancake, in this analogy, holds more syrup.
- Plate Separation: A smaller gap between plates increases capacitance, just like squishing those pancakes closer together.
Dielectric Constant
The dielectric constant, often represented by the symbol \( \epsilon \), is a measure of a material's ability to store electrical energy in an electric field. It's an important factor in capacitors, as it impacts how much electric charge the capacitor can store.
When a dielectric material is placed between the plates of a capacitor, it increases the overall capacitance by reducing the electric field's strength between the plates. This allows the capacitor to store more charge at the same voltage.
Here's why this matters:
When a dielectric material is placed between the plates of a capacitor, it increases the overall capacitance by reducing the electric field's strength between the plates. This allows the capacitor to store more charge at the same voltage.
Here's why this matters:
- Material Impact: Different materials have different dielectric constants. Materials with higher dielectric constants enable greater storage of energy.
- Capacitance Boost: The presence of a dielectric material like plastic, ceramic, or liquid increases the storage capacity of a capacitor without altering the physical space it occupies.
Capacitor Formula
The capacitor formula is a handy equation used to compute the capacitance of a parallel-plate capacitor, which is given by: \[ C = \epsilon \frac{A}{d} \]
Let’s break down what each component represents:
Let’s break down what each component represents:
- \( C \): The capacitance, typically measured in Farads, is the capacity of a capacitor to store charge.
- \( \epsilon \): The dielectric constant, which determines how effectively the material between the plates can store and maintain charge.
- \( A \): The area of one of the plates. Larger areas permit more charge to accumulate.
- \( d \): The distance between the two plates. Smaller separations can lead to higher capacitance because the plates' electric fields influence each other more effectively.