九年级英语周报新目标11答案

17.B由安培定则可判断出左侧线圈产生的磁场方向向上,经铁芯后在霍尔元件处的磁场方向向下,选项A错误;通过霍尔元件的磁场方向向下,由左手定则可知,霍尔元件中载流子受到的磁场力向右,导电物质偏向接线端B,导电物质为电子,则接线端B的电势低于接线端D的电势,选项B正确;仅将两电源反向接入电路,磁场反向,电流反向,霍尔元件中导电物质受到的磁场力不变,电压表的示数不变,选项C错误;若适当减,电流产生的磁场增强,通过霍尔元件的磁场增强;增大R2,流过霍尔元件的电流减弱;霍尔元件产生电压U=k的变化不能确定,选项D错误

第一节Dear Mr GeorgeI am Li Hua, a volunteer of the activity"Englishi Communication to the Mountains". Now, I'm writing toexpress my sincere apology to you for not being present atthe activity to be held next Monday.The reason for my absence is that I suddenly fell illMy parents sent me to hospital, and I have to stay therefor a week. As for my volunteer work, I have asked myclassmate Tom to do it.Sincerely hoping that you can accept my apologiesYours.Li Hua

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