半径为R的均匀带电球面,若其电荷面密度为<img src="https://zk.995w.com/lqwvjeImg/cb/cb6ed63ca49917d9cfdea138dd6cf27c.png"style="width:16px;height:15px;">,则在距离球面R处的电场强度大小为: ( )<br>· <img src="https://zk.995w.com/lqwvjeImg/a5/a59139fb9c409e50ce09823a52744875.png"style="width:22px;height:45px;">.<br>· <img src="https://zk.995w.com/lqwvjeImg/5f/5f33e73e4ae12a02ec2e21519b0822de.png"style="width:30px;height:45px;">.<br>· <img src="https://zk.995w.com/lqwvjeImg/c8/c8cd7f39ff7f7daebd33328a04412b89.png"style="width:30px;height:45px;">.<br>· <img src="https://zk.995w.com/lqwvjeImg/16/16e2d4f4ca498472ffad86200d2a8d99.png"style="width:29px;height:45px;">.