1.* * * In the emitter amplifier, the function of the collector resistor RC is ().

A: realize current amplification B: transistor current amplification is converted into voltage amplification C: current amplification and voltage amplification D: stabilize the operating point.

42. Y connection of three-phase power supply, UB = 220∞- 10 volts, UAB= () volts.

a:220∠20 B:220∠ 140 C:380∠ 140D:380∠20

43. The initial phase angle of sinusoidal AC voltage φ=-π/6, when t=0, its instantaneous value will be ().

A: greater than zero b: less than zero c: equal to zero d: maximum value

44. The condition of LC series resonance is ().

a:ωL =ωC B:L = C C:ωL = 1/ωC D:XL = 2πfL

45. If the voltage across an element in the circuit is U =100 sin (100 π t+50) V and the current is I =10 sin (100 π t+140) A, then the element is.

A: resistance b: inductance c: capacitance d: resistance-capacitance

46. The phase relationship between current and voltage in resistance-capacitance AC circuit is current (√√) voltage.

A: lead 90 B, lag 90°C, in-phase d, lead 0 ~ 90.

Second, multiple-choice questions:

1. In a sinusoidal AC circuit, the following formula is correct ().

a:Ic = duc/dt B:Ic = jwcU C:UC =-jwct D:XC = 1/WC E:QC = uisinφ

2. There are three basic logic operation circuits, namely () circuit.

A: NAND gate B: AND gate C: NOR gate D: NOR gate E: OR gate

3. For a three-phase symmetrical AC circuit, the following conclusion is correct regardless of star or triangle connection ().

a:P = 3 umimcosφB:S = 3 umim C:Q = u 1 I 1 sinφD:S = E:S = 3UI

4. The coupling form between poles of multistage amplifier is ().

A: diode b: resistor c: capacitance d: transformer e: DC.

5. The most basic logic circuit of electronic circuit is ().

A: AND gate B: NOT gate C: NAND gate D: OR gate E: XOR.

6. Kirchhoff's law has ().

A: node current law b: loop voltage law c: path current law d: node voltage law

7. The three elements of sinusoidal alternating current are ().

A: maximum b: initial phase angle c: angular frequency d: series connection e: parallel connection

8. China's three-phase power transformer wiring group has (), etc.

a:Y/δ- 1 1 B:Y0/δ- 1 1 C:Y0/Y- 12

d:Y/Y- 12 E:Y/δ-7

9. The methods to artificially improve the power factor are ().

A: Suitable capacitor in parallel B: Suitable capacitor in series C: Large reactor in parallel D: Large capacitor in series E: Suitable inductor in series.

10. Three-phase load symmetry is ().

Answer: The impedance values of each phase are equal; B: the impedance values of each phase are different; C: phase complex angle difference120d; The complex angles of all phases are equal; E: phase complex angle difference 180.

1 1. The condition of thyristor conduction is ().

A, applying a DC voltage between an anode and a cathode; B: A reverse voltage is applied between the anode and the cathode.

C: DC voltage D is applied between the control electrode and the cathode; reverse voltage E is applied between the control electrode and the cathode; DC voltage is applied between the anode and the control electrode.

12. Sinusoidal AC circuit, which of the following equations is correct? ( )

a:IL = U/XL B:UC = Xcic C:U = Ri D:X = X 1+X2+X3 E:Z = Z 1+Z2+Z3

13. How many forms are there for phasor symbols of alternating current? ( )

A: algebraic formula b: trigonometric formula c: geometric formula d: exponential formula e: polar coordinate formula

14. The advantage of improving the power factor is ().

A: It can give full play to the capacity of power supply equipment B: It can improve the output of motor C: It can reduce the power loss of the line.

D: It can reduce the starting current of the motor. E: it can improve the motor power.

15. When the bridge is externally connected with power supply, the phenomenon of () will appear.

A: damaged resistance B: reduced sensitivity C: reduced accuracy D: unable to zero E: inaccurate reading.

16. The method of turning off the thyristor is ().

A: Cut off the control electrode voltage B: Cut off the anode power supply C: Reduce the forward anode voltage D: Apply the reverse voltage E to the anode: Reduce the control electrode current.

17. When the three power supplies are connected Y, the line voltage is () times of the phase voltage, and the line voltage is ahead of the phase voltage ().

A: B: C: Sixty days: Thirty days: Ninety days.

18. A three-phase symmetrical inductive load is connected to the same power supply with triangle and Y shape respectively, and the following conclusions are drawn: ()

A: load phase voltage: u δ phase =3UY phase B: line current: I δ phase =3IY C: power: P δ = 3PYD: phase current: II δ phase = IY E: withstand in-phase voltage.

19. In power system, the main function of reactive power compensation with parallel compensation capacitor is ().

A: Improve power factor B: Improve equipment output C: Reduce power loss and electric energy loss D: Improve voltage quality E: Improve lightning protection performance of overhead lines.

20.RLC series sine AC circuit, when XL=XC, the circuit resonates, and the resonance characteristic is ().

A: The voltage on the capacitor is equal to the voltage on the inductor, and the direction is opposite. B: the maximum current in the circuit. C: the minimum impedance in the circuit.

D: the reactive power in the circuit is 0 E: the voltage on the resistor is equal to the applied voltage, and the direction is opposite.

2 1. Single-phase transformer wiring group determination method is ().

A: DC method B: resistance method C: AC method D: power measurement method E: AC current method

22. Thevenin's theorem applies to the external circuit as () circuit.

A: linear b: rectification c: amplification d: nonlinear e: saturation

23. It is known that the ground potentials of the three pins of the triode in the amplification circuit are (1)0V, (2)0.7V and (3)6V. The electric field corresponding to each pin of the triode is ().

A: (1) is the base B: (2) is the base C: (1) is the emitter D: (3) is the collector E: (3) is the emitter.

24. The limit parameters of triode mainly include ().

A: maximum allowable collector current ICM B: collector-emitter breakdown voltage (base open circuit) UCEO C: collector-base reverse saturation current ICBO

D: penetration current ICEO E: maximum allowable dissipation power PCN of collector.

25. The three configurations of the amplifier circuit are ().

A: * * * Emitter amplification B: * * * Collector amplification C: Saturation D: Cut-off E: * * * Base amplification

26. Let three-phase sinusoidal alternating current ia = imsin Ω t and ib be ().

a:IB = Imsin(ωt- 120)B:IB = Imsin(ωt+240)

c:IB = Imsin(ωt-240)D:IB = Imsin(ωt+ 120)E:IB = Imsin(ωt 0)

27. The three working states of triode are ().

A: open circuit B: amplification C: cut-off D: short circuit E: saturation

28. The blocking effect of thyristor is ().

A: forward blocking b: reverse blocking c: forward bias d: reverse bias e: gate bias.

29. The significance of improving the power factor is ().

A: Make full use of equipment capacity B: Improve power supply quality C: Reduce line power and voltage loss D: Save economic expenses E: Save line investment.

30. The three configurations of the amplifier circuit are ().

Answer: Low frequency amplifier.

B: * * * collector amplifier C: * * base amplifier D: multipole amplifier E: * * * emitter amplifier