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Ch 23: The Electric Field
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 23, Problema 68b

A rod of length LL lies along the yy-axis with its center at the origin. The rod has a nonuniform linear charge density λ=a∣y∣ λ=a|y|, where a is a constant with the units C/m2. Determine the constant a in terms of LL and the rod's total charge QQ.

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Step 1: Understand the problem. The rod has a nonuniform linear charge density λ = a|y|, where λ represents the charge per unit length at a given point y along the rod. The total charge Q is distributed along the rod of length L, and we need to find the constant 'a' in terms of Q and L.
Step 2: Express the total charge Q as the integral of the linear charge density λ over the length of the rod. Since the rod lies along the y-axis and is centered at the origin, its endpoints are at y = -L/2 and y = L/2. The total charge is given by: Q = ∫(λ dy) = ∫(a|y| dy), where the integral is evaluated from y = -L/2 to y = L/2.
Step 3: Break the integral into two parts to account for the absolute value of y. For y < 0, |y| = -y, and for y > 0, |y| = y. Therefore, the integral becomes: Q = ∫(a(-y) dy) from y = -L/2 to y = 0 + ∫(a(y) dy) from y = 0 to y = L/2.
Step 4: Solve each integral separately. For the first integral (from y = -L/2 to y = 0), substitute |y| = -y, and for the second integral (from y = 0 to y = L/2), substitute |y| = y. Combine the results to express Q in terms of 'a' and 'L'.
Step 5: Rearrange the equation to solve for 'a'. Since Q is known, isolate 'a' by dividing both sides of the equation by the appropriate terms involving L. This will give the expression for 'a' in terms of Q and L.

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Linear Charge Density

Linear charge density (λ) is defined as the amount of electric charge per unit length along a line. In this case, the charge density varies with the position along the rod, given by λ = a|y|, indicating that the charge density increases linearly with the distance from the center of the rod. Understanding this concept is crucial for calculating the total charge distributed along the length of the rod.
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Total Charge Calculation

The total charge (Q) of the rod can be calculated by integrating the linear charge density over the length of the rod. This involves setting up an integral from -L/2 to L/2, where the charge density λ varies with y. The result of this integration will provide a relationship between the constant a, the length L, and the total charge Q, which is essential for solving the problem.
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Integration in Physics

Integration is a fundamental mathematical tool used in physics to find quantities that accumulate over a continuous range, such as charge, mass, or energy. In this context, it allows us to sum the contributions of the varying charge density along the length of the rod. Mastery of integration techniques is necessary to derive the total charge from the given linear charge density function.
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