利用现有素材,自己画的。凑合用吧
http://image.baidu.com/i?ct=503316480&z=&tn=baiduimagedetail&word=%B5%C8%CA%C6%C3%E6%D3%EB%B5%C8%B8%DF%CF%DF%B5%C4%B6%D4%B1%C8&in=6774&cl=2&lm=-1&pn=1&rn=1&di=43539320805&ln=78&fr=&fmq=&ic=&s=&se=&sme=0&tab=&width=&height=&face=&is=&istype=#pn1&-1&di43539320805&objURLhttp%3A%2F%2Fwt.zjzszx.cn%2Fimagematerial%2Fupload%2Fwl%2F9PPNXR6HA2BECTMA.jpg&fromURLhttp%3A%2F%2Fwt.zjzszx.cn%2Fimagematerial%2Fview.asp%3Fid%3D22491&W804&H1121
把图中的正电荷改成负电荷,电场线箭头方向相反就可以了。