Calculus: Early Transcendentals (2nd Edition)

Published by Pearson
ISBN 10: 0321947347
ISBN 13: 978-0-32194-734-5

Chapter 14 - Vector Calculus - 14.8 Divergence Theorem - 14.8 Exercises - Page 1144: 13

Answer

The flux across the sphere is zero.

Work Step by Step

Divergence Theorem: It states that the flux across the boundary of $R$ is equal to the net contraction or expansion of the vector field $F$ within the region $R$.This implies that $\int\int F \cdot n d C=\int\int\int \nabla \cdot F dR$ Here, $R$ defines the connected and region in space which is oriented by boundary $C$ and n denotes the outward flux unit normal vector on boundary $C$. In order to compute the net outward flux of the given vector field, we will firstly compute $\nabla \cdot F$. Now, we have: $\nabla \cdot F=\lt \dfrac{\partial}{\partial x}, \dfrac{\partial}{\partial y}, \dfrac{\partial}{\partial z} \gt \cdot \lt 2x-y, x, -2x\gt\\=\dfrac{\partial}{\partial x}(2z-y) +\dfrac{\partial}{\partial y}(x)+\dfrac{\partial}{\partial z}(-2x)\\=0$ Thus, $\int\int F \cdot n d C=\int\int\int \nabla \cdot F dR=0$ This implies that the flux across the sphere is zero by using the divergence theorem.
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