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【单选题】
T68卧式镗床电气线路图如图6所示,如果低速模式下按下SB3,主轴电机不能正常反转,快速移动电动机可以正常工作,经实验发现KM3无法正常得电但KA2可以得电,采用电压分阶法,测得SQ4的110号线110V,SQ的111号线110V,KM3的111号线110V,KA2的130号线110V,则故障点是A.
故障点7
B.
故障点8
C.
故障点10
D.
故障点11
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举一反三
【单选题】When a p-n junction is reverse-biased, its junction resistance is ( ).
A.
high
B.
low
C.
determined by the components that are external to the device
D.
constantly changing
【单选题】when we apply reverse bias to a P-N junction at less than the avalanche voltage, the junction
A.
does not conduct
B.
conducts intermittently
C.
conducts fairly well
D.
conducts very well
【单选题】When a p-n junction is reverse-biased, the depletion layer is ________ and the device acts as a near-perfect ________( ).
A.
narrowed; conductor
B.
narrowed; insulator
C.
widened; conductor
D.
widened; insulator
【单选题】Light-emitting diodes emit light when the p-n junction is ( ).
A.
forward-biased
B.
reverse-biased
C.
zero biased
D.
operating in the Zener region
【单选题】When we forward-bias a P-N junction ,it fails to conduct
A.
unless the junction has enough capacitance
B.
if the applied voltage is less than the forward breakover voltage
C.
if the applied voltage exceeds the avalanch voltage
D.
unless the voltage remains constant
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