中科新闻网股票 外源融资 为什么:急!!!!! 计数
来源：百度文库 编辑：中科新闻网 时间：2024/04/27 23:07:44
In a television tube the picture is formed by streams of electrons hitting the screen. The current is 20mA. How much electric charge hits the screen in 30 minutes?
e=1.6*10^-19 c
20mA=0.02A
The anwser is 0.02A/e*30*60=225*10^18