Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 16 - Vector Calculus - 16.5 Curl and Divergence - 16.5 Exercises - Page 1149: 9

Answer

(a) $divF$ is negative. (b) $curlF$ is zero.

Work Step by Step

(a) The vector field shown is a 2D vector field of the form $F=Pi+Qj$ We know that $divF=\frac{∂P}{∂x}+\frac{∂Q}{∂y}$ Here $\frac{∂P}{∂x}=0$, since the $x$ components of the vectors are $0$. $\frac{∂Q}{∂y}$ is negative, since the $y$ components of the vectors are deceasing in length, as we move along the positive $y-direction$. Which implies that divergence is negative. That is, $divF=\frac{∂P}{∂x}+\frac{∂Q}{∂y}=0+(-ve)=-ve$ Hence, $divF$ is negative. (b) The vector field shown is a 2D vector field of the form $F=Pi+Qj$ We know that $curlF=(\frac{∂Q}{∂x}-\frac{∂P}{∂y})k$ Here $\frac{∂Q}{∂x}=0$, since the $y$ components of the vectors have same length, as we move along the positive x-direction. $\frac{∂P}{∂y}$ is $0$, since the $x$ components of the vectors are $0$. That is,$curlF=(\frac{∂Q}{∂x}-\frac{∂P}{∂y})k=(0-0)k=0$ Hence, $curlF$ is zero.
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