Chapter 2573*P25.69(a)Vkqrrrreee=−=−121221bgFrom the figure, for ra>>,rr a2−≅cosθ.ThenVakpr≅≅22coscos.(b)EVrrre=−∂∂=23cosIn spherical coordinates, the component of the gradient is 1r∂∂FHGIKJ.FIG. P25.69Therefore,ErVre∂∂FHGIKJ=13sin.For >>Erre023°=afandEr900,E00andEre903.These results are reasonable for >>. Their directions are as shown in Figure 25.13 (c).However, for rE→→∞,.This is unreasonable,
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