u= 100sin(ωt+10°)V、i1= 2sin(ωt+100°)A,i2 =-4sin(ωt+190°)A。u,i1,i2的有效值分别为多少
A. 70.7V;1.414A;-2.828A
B. 70.7V;2.828A;1.414A;
C. 100;2A;4A;
D. 70.7V;1.414A;2.828A
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u= 100sin(ωt+10°)V、i1= 2sin(ωt+100°)A,i2 =-4sin(ωt+190°)A。u越前与i1,i2的相位差
A. 90°；0°
B. 0°；90°
C. -90°；0°
D. 0°；-90°
下列正弦量的相量表达式分别为：i1=3sinωt ,i2 =4sin(ωt-150°),i3=- 5sin(ωt- 60°)i4 =6cos(ωt+30°).
A. 3∠0°；4∠-150°；5∠120°；6∠120°
B. 3∠0°；4∠150°；5∠120°；6∠120°
C. 3∠0°；4∠-150°；5∠-60°；6∠120°
D. 3∠0°；4∠-150°；5∠120°；6∠30°
一个电阻R=15Ω、电感L=12mH的线圈与C=5uF的电容器相串联,接在电压u =100sinωt V的电源上，ω=5000rad/s。试求电流i、电容器端电压uc.和线圈端电压uw 。
A. i= 4 sin(ωt+53.10°) AuC =160 sin(ωt -143.1°) VuC =248sin(ωt +22.9°) V
B. i= 4 sin(ωt-53.10°) AuC =160 sin(ωt -143.1°) VuC =248sin(ωt -22.9°) V
C. i= 4 sin(ωt-53.10°) AuC =160 sin(ωt -143.1°) VuC =248sin(ωt +22.9°) V
D. i= 4 sin(ωt-53.10°) AuC =160 sin(ωt +143.1°) VuC =248sin(ωt +22.9°) V
What has replaced the era when people could safely keep their front door unlocked?It has been replaced by an era _______________.
A. when people can afford a lot of security devices
B. when people emloy various security devices at home
C. when people attach importance to their life quality
D. when people are keen to purchase insurance
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