在电场中某点放一电量为6×10﹣7C的负电荷,该电荷受到的电场力为3×10﹣5 N,方向水平向西,则该点的电场强度为____,方向____.若在该点改放一个正电荷,则该点电场强度方向是____.
阅读对话,判断正误,对的写“正确”错的写“错误”
Mingming: What are you doing, Lingling?
Lingling: I'm training. I'm going to do the high jump. What are you going to do for Sports Day?
Mingming: I'm going to run the 100 metres.
如图所示实验中,①、④为用紫色石蕊溶液润湿的棉球,②、③为用石蕊溶液染成紫色并干燥后的棉球.下列能说明CO2密度大于空气且能溶于水的现象是( )
下列对染色质和染色体的说法,正确的是