Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Published by Pearson
ISBN 10: 0321740904
ISBN 13: 978-0-32174-090-8

Chapter 25 - Electric Charges and Forces - Exercises and Problems - Page 748: 61

Answer

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Work Step by Step

The electric field direction is toward the charge since it is a negative charge. We chose the origin to be point 1. And as we see below, the angle $\theta_1$ is in the first quadranet, so $$\theta_1 =\color{red}{\bf 60^\circ}$$ And since angle $\theta_2$ is in the second quadranet, $$\theta_2=180^\circ -60^\circ =\color{red}{\bf 120^\circ}$$ $\Rightarrow$ At point (1), the electric field magnitude is given by $$E_1=\dfrac{kq}{r_1^2} $$ Plugging the known; $$E_1=\dfrac{(8.99\times 10^9)(2\times 10^{-9})}{(0.01)^2} $$ [we neglected the sign of the charge since we are focusing on the electric field direction by angles] $$E_1=\color{red}{\bf1.8\times 10^5}\;\rm N/C$$ and its direction is $60^\circ$ counterclockwise from $+x$-direction. $\Rightarrow$ At point (2), the electric field magnitude is given by $$E_2=\dfrac{kq}{r_2^2} $$ Plugging the known; $$E_2=\dfrac{(8.99\times 10^9)(2\times 10^{-9})}{(0.01)^2} $$ $$E_2=\color{red}{\bf1.8\times 10^5}\;\rm N/C$$ and its direction is $120^\circ$ counterclockwise from $+x$-direction.
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