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Ch 31: Electromagnetic Fields and Waves
Knight Calc - Physics for Scientists and Engineers 5th Edition
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Non è quello che usi tu?Cambia libro di testo
Capitolo 31, Problema 37b

A 10 A current is charging a 1.0-cm-diameter parallel-plate capacitor. What is the magnetic field strength at a point 2.0 mm radially from the center of the capacitor?

Guida verificata passo dopo passo
1
Step 1: Recognize that the problem involves calculating the magnetic field strength due to a changing electric field in a parallel-plate capacitor. This is related to Maxwell's equations, specifically the Ampère-Maxwell law, which accounts for the displacement current.
Step 2: Write the Ampère-Maxwell law in integral form: \( \oint \mathbf{B} \cdot d\mathbf{l} = \mu_0 (I + I_d) \), where \( I_d \) is the displacement current. For this problem, the displacement current \( I_d \) is equal to the conduction current \( I \), which is given as 10 A.
Step 3: Use the symmetry of the problem to simplify the calculation. The magnetic field \( B \) is tangential to a circular path around the axis of the capacitor, and its magnitude is constant at a given radius \( r \). The integral simplifies to \( B \cdot 2\pi r \).
Step 4: Solve for \( B \) using the equation \( B \cdot 2\pi r = \mu_0 I \). Rearrange to find \( B = \frac{\mu_0 I}{2\pi r} \), where \( \mu_0 \) is the permeability of free space (\( \mu_0 = 4\pi \times 10^{-7} \ \mathrm{T \cdot m/A} \)), \( I \) is the current (10 A), and \( r \) is the radial distance (2.0 mm or 0.002 m).
Step 5: Substitute the values into the formula \( B = \frac{\mu_0 I}{2\pi r} \) to calculate the magnetic field strength. Ensure all units are consistent (e.g., meters for distance, amperes for current).

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Concetti chiave

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Capacitance

Capacitance is the ability of a capacitor to store charge per unit voltage. It is defined by the formula C = Q/V, where C is capacitance, Q is the charge stored, and V is the voltage across the plates. In this case, the parallel-plate capacitor's capacitance depends on its plate area and the distance between the plates, influencing how much charge it can hold.
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Capacitors & Capacitance (Intro)

Magnetic Field due to Current

A magnetic field is generated around a conductor when an electric current flows through it. According to Ampère's Law, the magnetic field strength (B) at a distance (r) from a long straight conductor carrying current (I) can be calculated using the formula B = (μ₀I)/(2πr), where μ₀ is the permeability of free space. This principle is essential for determining the magnetic field around the capacitor.
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Magnetic Field Produced by Straight Currents

Radial Distance in Magnetic Fields

Radial distance refers to the distance measured outward from the center of a circular object, such as the plates of a capacitor. In this context, the magnetic field strength is evaluated at a specific radial distance (2.0 mm) from the center of the capacitor. Understanding how the magnetic field varies with distance is crucial for accurately calculating its strength at that point.
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Magnetic Fields and Magnetic Dipoles
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