半径为r的均匀带电球面1,带有电荷q,其外有一同心的半径为R的均匀带电球面2,带有电荷Q,则此两球面之间的电势差U1-U2为:( )<br>· <img src="https://zk.995w.com/lqwvjeImg/a5/a53fdc9cd54aff9931f54946ee0438c6.png"style="width:96px;height:46px;"> .<br>· <img src="https://zk.995w.com/lqwvjeImg/33/33dfd08dbdfd437c7eb7068f2349dc01.png"style="width:96px;height:46px;"> .<br>· <img src="https://zk.995w.com/lqwvjeImg/3f/3f2a2baad103df282945c2ab679ce766.png"style="width:99px;height:46px;"> .<br>· <img src="https://zk.995w.com/lqwvjeImg/a0/a0dc14fdc85c380b9f942a133616d46c.png"style="width:44px;height:44px;"> .