电子管的真空度约为<img src="https://nimg.ppkao.com/2019-04/wuacheng/2019042416340137984.jpg?sign=a0051ee9f087905c3d3730f784344f52&t=62d7c208" />HG，设气体分子的有效直径为<img src="https://nimg.ppkao.com/2019-04/wuacheng/2019042416342012869.jpg?sign=3f9db96145997a1654f4173fddc852bb&t=62d7c208" />求<img src="https://nimg.ppkao.com/2019-04/wuacheng/2019042416345188675.jpg?sign=7c29a6d9eebd9fe679735327f988b8a8&t=62d7c208" />时单位体积内的分子数，平均自由程和碰撞频率。