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A 5.00-pF, parallel-plate, air-filled capacitor with circular plates is to be used in a circuit in which it will be subjected to potentials of up to 1.00 \(\times\) 10\(^2\) V. The electric field between the plates is to be no greater than 1.00 \(\times\) 10\(^4\) N/C. As a budding electrical engineer for Live-Wire Electronics, your tasks are to (a) design the capacitor by finding what its physical dimensions and separation must be; (b) find the maximum charge these plates can hold.

Short Answer

Expert verified
Plate separation is 1.0 cm, plate radius is 4.24 cm; the maximum charge is 5.00 x 10^-10 C.

Step by step solution

01

Calculate the Plate Separation

Use the formula for the electric field between the plates of a parallel-plate capacitor: \( E = \frac{V}{d} \). Given \( E = 1.00 \times 10^4 \text{ N/C} \) and \( V = 1.00 \times 10^2 \text{ V} \), solve for \( d \):\[ d = \frac{V}{E} = \frac{1.00 \times 10^2}{1.00 \times 10^4} = 0.01 \text{ m} \] or \( 1.0 \text{ cm} \).
02

Calculate the Area of the Plates

Use the formula for the capacitance of a parallel-plate capacitor: \( C = \frac{\varepsilon_0 A}{d} \).Rearrange to find the area \( A \): \[ A = \frac{C \cdot d}{\varepsilon_0} = \frac{5.00 \times 10^{-12} \cdot 0.01}{8.85 \times 10^{-12}} \approx 0.00565 \text{ m}^2 \].
03

Calculate the Radius of the Plates

For a circular plate, area is \( A = \pi r^2 \). Solve for \( r \):\[ r = \sqrt{\frac{A}{\pi}} = \sqrt{\frac{0.00565}{\pi}} \approx 0.0424 \text{ m} \] or \( 4.24 \text{ cm} \).
04

Calculate Maximum Charge

Use the formula for charge on a capacitor: \( Q = C \times V \).\[ Q = 5.00 \times 10^{-12} \text{ F} \times 1.00 \times 10^2 \text{ V} = 5.00 \times 10^{-10} \text{ C} \].

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Electric Field
An electric field is a force field surrounding a charged particle. For capacitors, it is the field between the two plates. Think of it as the invisible energy that moves charges between the plates. The formula to calculate the electric field (\( E \)) between the plates of a parallel-plate capacitor is given by:\( E = \frac{V}{d} \).Here, \( V \) is the voltage applied across the plates, and \( d \) is the separation between them. The electric field tells us how strong the effect of the voltage is, and it ensures that the capacitor can hold its charge without breaking down. In our exercise, the electric field must not exceed \( 1.00 \times 10^4 \, \text{N/C} \), which means we need to adjust the distance \( d \) to keep the electric field within safe limits.
  • Electric fields influence how quickly charges move between plates.
  • A strong electric field can cause dielectric breakdown, damaging the capacitor.
  • Designing a capacitor requires careful attention to balancing electric field strength.
Capacitance Calculation
Capacitance is a measure of a capacitor's ability to store charge. It is determined by the physical attributes of the capacitor, such as the area of the plates (\( A \)), the separation distance (\( d \)), and the permittivity of the material between the plates (\( \varepsilon_0 \)). The general formula for the capacitance (\( C \)) of a parallel-plate capacitor is:\( C = \frac{\varepsilon_0 A}{d} \).In our scenario, with a given capacitance of \( 5.00 \, \text{pF} \), and knowing the separation \( d \) and the constant \( \varepsilon_0 \) of air, we can calculate the necessary area of the plates to achieve this capacitance. This involves rearranging the formula to solve for \( A \):\[ A = \frac{C \cdot d}{\varepsilon_0} \].With these values, one could solve not only the plate area but other design parameters of the capacitor.
  • Larger plate areas increase capacitance.
  • Smaller separation distances increase capacitance.
  • Changing the dielectric material changes capacitance significantly.
Charge on a Capacitor
The charge stored in a capacitor's plates is essential as it determines how much electrical energy the capacitor can release when needed. This is computed using the formula:\( Q = C \times V \).Here, \( Q \) is the charge in coulombs, \( C \) is the capacitance in farads, and \( V \) is the voltage across the plates. In this case, the maximum charge is determined by applying the maximum voltage that the capacitor is designed for. Using the given values, the charge stored is calculated to be \( 5.00 \times 10^{-10} \, \text{C} \). This value tells us how much energy the capacitor holds and thus how much it can supply when connected in a circuit.
  • Higher voltage leads to more charge stored, up to the breakdown voltage.
  • Capacitors release stored energy quickly, useful for various applications.
  • Stored charge can be lethal if mishandled; design safety is paramount.

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Most popular questions from this chapter

A parallel-plate capacitor has plates with area 0.0225 m\(^2\) separated by 1.00 mm of Teflon. (a) Calculate the charge on the plates when they are charged to a potential difference of 12.0 V. (b) Use Gauss's law (Eq. 24.23) to calculate the electric field inside the Teflon. (c) Use Gauss's law to calculate the electric field if the voltage source is disconnected and the Teflon is removed.

The plates of a parallel-plate capacitor are 3.28 mm apart, and each has an area of 9.82 cm\(^2\). Each plate carries a charge of magnitude 4.35 \(\times\) 10\(^{-8}\) C. The plates are in vacuum. What is (a) the capacitance; (b) the potential difference between the plates; (c) the magnitude of the electric field between the plates?

A parallel-plate air capacitor is to store charge of magnitude 240.0 pC on each plate when the potential difference between the plates is 42.0 V. (a) If the area of each plate is 6.80 cm\(^2\), what is the separation between the plates? (b) If the separation between the two plates is double the value calculated in part (a), what potential difference is required for the capacitor to store charge of magnitude 240.0 pC on each plate?

A cylindrical capacitor has an inner conductor of radius 2.2 mm and an outer conductor of radius 3.5 mm. The two conductors are separated by vacuum, and the entire capacitor is 2.8 m long. (a) What is the capacitance per unit length? (b) The potential of the inner conductor is 350 mV higher than that of the outer conductor. Find the charge (magnitude and sign) on both conductors.

A 20.0-\(\mu\)F capacitor is charged to a potential difference of 800 V. The terminals of the charged capacitor are then connected to those of an uncharged 10.0-\(\mu\)F capacitor. Compute (a) the original charge of the system, (b) the final potential difference across each capacitor, (c) the final energy of the system, and (d) the decrease in energy when the capacitors are connected.

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