照样子,用两种计时法写出钟面上显示的时间.
be bound to; junior to; take... seriously; as long as;
help out; in all; be attached to; at one time
如图所示电路中滑动变阻器R1的阻值为200Ω,电阻R2阻值为300Ω,电源电压为6V,当滑片由a端滑到b端,电压表的示数的变化范围是( )