/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 24 A conductor carries a current th... [FREE SOLUTION] | 91Ó°ÊÓ

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A conductor carries a current that is decreasing exponentially with time. The current is modeled as \(I=I_{0} e^{-t / \tau},\) where \(I_{0}=3.00 \mathrm{A}\) is the current at time \(t=0.00 \mathrm{s}\) and \(\tau=0.50 \mathrm{s}\) is the time constant. How much charge flows through the conductor between \(t=0.00 \mathrm{s}\) and \(t=3 \tau ?\)

Short Answer

Expert verified
The total charge that flows through the conductor between \(t=0.00\,\text{s}\) and \(t=3\tau\) is approximately \(2.32\,\text{C}\).

Step by step solution

01

Identify the current function and limits of integration

Given the current function \(I(t) = I_0 e^{-t/\tau}\), where \(I_0 = 3.00\,\text{A}\) and \(\tau = 0.50\,\text{s}\). We are asked to find the charge that flows through the conductor between \(t=0.00\,\text{s}\) and \(t=3\tau\), so our limits of integration will be from 0 to \(3\tau\).
02

Integrate the current function with respect to time

Let \(Q\) be the charge. To find \(Q\), we will integrate the current function with respect to time: \[Q(t) = \int I(t) \, dt = \int I_0 e^{-t/\tau} \, dt\]
03

Perform integration and find the indefinite integral

To integrate the given function, we use the substitution method. Let \(u=-t/\tau\), so \(\frac{du}{dt}=-1/\tau\). Then, the integration becomes: \[Q(t) = \int I_0 e^{u} \left(-\tau\right) du\] Now, integrate the function: \[Q(t) = -I_0\tau\int e^{u} du\] \[Q(t) = -I_0\tau\left(e^u\right) + C\]
04

Substitute the variable back and write the expression for charge in terms of time

Substitute \(u = -t/\tau\) back into the expression for the charge: \[Q(t) = -I_0\tau\left(e^{-t/\tau}\right) + C\]
05

Evaluate the definite integral by applying the limits of integration

Now we will evaluate the definite integral over the given time range \([0, 3\tau]\): \[Q = \int_{0}^{3\tau} I_0 e^{-t/\tau} \, dt\] \[Q = \left[-I_0\tau\left(e^{-t/\tau}\right)\right]_{0}^{3\tau}\] Plug in the limits and simplify: \[Q = -I_0\tau\left(e^{-3} - 1\right)\]
06

Substitute the given values and find the charge Q

Now, substitute the given values of \(I_0 = 3.00\,\text{A}\) and \(\tau = 0.50\,\text{s}\) into the expression for the charge: \[Q = - (3.00\,\text{A})(0.50\,\text{s})\left(e^{-3} - 1\right)\] Calculate the numerical value for the charge: \[Q \approx 2.32\,\text{C}\] Thus, the total charge that flows through the conductor between \(t=0.00\,\text{s}\) and \(t=3\tau\) is approximately \(2.32\,\text{C}\).

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Key Concepts

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

Understanding Electric Current
Electric current is a fundamental concept in physics, particularly in the field of electromagnetism. It refers to the flow of electric charge through a conductor, such as a wire, and is typically measured in amperes (A). Understanding current is crucial when analyzing electrical circuits and the behavior of electrons under various conditions. The behavior of electric current is often represented using mathematical models, one of which is the exponentially decreasing current. This model illustrates how the current diminishes over time, which is useful in applications such as the discharge of a capacitor in an electric circuit.

In the given exercise, the current at any given moment is described by the equation \(I=I_{0} e^{-t / \tau}\), where \(I_{0}\) is the initial current and \(\tau\) is the time constant, a parameter that depicts how quickly the current decays. Such equations are pivotal as they allow physicists and engineers to predict the behavior of the current over time and to calculate related quantities, such as the total charge flow.
Integration in Physics
Integration, a fundamental mathematical tool in calculus, is widely used in physics to calculate various quantities that change over time. This process involves finding the total value accumulated by a function between two points, often referred to as the limits of integration. In the context of electric current and charge, integration is used to determine the total amount of charge that flows through a conductor over a specified time interval.

In the provided exercise, the concept of integration allows us to find the charge flow from the changing current by integrating the current function over a time period. The ability to integrate correctly is essential for students and professionals in physics and engineering, as it provides a means to derive quantities that are not directly measurable but that we can infer from other related variables.
Exponential Decay in Physics
Exponential decay is a pattern of reduction over time that can be found in various physical phenomena. It describes processes where the quantity decreases at a rate proportional to its current value, resulting in a rapid decline that gradually slows over time. This concept is intricately linked to 'half-life' in radioactive decay, the discharging of capacitors in circuits, and damping in mechanical systems.

In our exercise, the electric current is subject to exponential decay, which means it reduces by a constant proportion in equal time intervals, governed by the time constant \(\tau\). Understanding the exponential decay process is important for students because it has numerous real-world applications ranging from nuclear physics to finance. It provides clear insights into how systems evolve and dissipate energy or value over time.
Charge Flow
Charge flow refers to the quantity of electric charge that moves past a specified point in a conductor within a certain time frame. It is quantified in coulombs (C), with one coulomb of charge representing an ample quantity of charge transfer. This measurement is not only crucial in circuit analysis but also in understanding the operation of various electronic devices and systems.

In the exercise, we calculate the total charge flow through the conductor by integrating the current over the given time interval. The resulting value represents the total amount of electric charge that has passed through the conductor between \(t=0.00\,\text{s}\) and \(t=3\tau\). This concept highlights the important relationship between current and charge: current is the rate of charge flow, and charge is the integral of current over time. It also emphasizes that charge, like energy, is conserved and can be tracked through complex systems in physics.

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Most popular questions from this chapter

A 12-V car battery is used to power a 20.00-W, 12.00-V lamp during the physics club camping trip/star party. The cable to the lamp is 2.00 meters long, 14 -gauge per wire with charge density of \(n=9.50 \times 10^{28} \mathrm{m}^{-3} .\) (a) What is the current draw by the lamp? (b) How long would it take an electron to get from the battery to the lamp?

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