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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 40

A 1.0 μF capacitor is discharged, starting at t = 0 s.The displacement current between the plates is Idisp=(10 A)exp(−t2.0 μs)I_{\(\text{disp}\)}=(10\(\text{ A}\))\(\exp\)\(\left\)(-\(\frac{t}{2.0\text{ }\)}\(\mu\[\text{s}\]\right\)). What was the capacitor’s initial voltage (ΔVC)₀?

Guida verificata passo dopo passo
1
Step 1: Understand the relationship between displacement current and the rate of change of electric field in a capacitor. The displacement current is given by the formula: Idisp=C⁢dVdt, where C is the capacitance and V is the voltage across the capacitor.
Step 2: Substitute the given displacement current expression Idisp=10⁢A⁢exp(-t/2.0⁢μs) into the formula for displacement current. This gives: 10⁢exp(-t/2.0⁢μs)=1.0⁢μF⁢dVdt.
Step 3: Rearrange the equation to isolate dVdt. This gives: dVdt=10⁢exp(-t/2.0⁢μs)1.0⁢μF.
Step 4: Integrate both sides with respect to time to find the voltage V. The integral of the displacement current expression is: 10⁢exp(-t/2.0⁢μs)dt. Evaluate this integral to find the voltage as a function of time.
Step 5: Determine the initial voltage (ΔVC)0 by evaluating the voltage expression at t=0. This involves substituting t=0 into the integrated voltage equation.

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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 as C = Q/V, where C is capacitance in farads, Q is the charge in coulombs, and V is the voltage across the capacitor. In this case, the capacitor has a capacitance of 1.0 μF, which indicates how much charge it can hold at a given voltage.
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Displacement Current

Displacement current is a concept introduced by James Clerk Maxwell to account for changing electric fields in capacitors. It is defined as Iₑₓₜ = ε₀(dΦ_E/dt), where ε₀ is the permittivity of free space and dΦ_E/dt is the rate of change of the electric field. In this problem, the displacement current is given as a function of time, indicating how the current changes as the capacitor discharges.
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Exponential Decay

Exponential decay describes the process by which a quantity decreases at a rate proportional to its current value. In the context of the displacement current, the equation Iₔᵢₛₚ = (10 A)exp(−t/2.0 μs) shows that the current decreases exponentially over time, which is characteristic of discharging capacitors. This behavior is crucial for determining the initial voltage across the capacitor.
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