 ## Friday, February 15, 2019

### Power Electronics (Objective Questions With Answers)

 A 240V, 50Hz supply feeds a highly inductive load of 50 Ohm resistance through a half controlled thyristor bridge. When the firing angle α=45°, the load power is
A. 418 W
B. 512 W
C. 367 W
D. 128 W

 A D.C. to D.C. chopper operates from a 48 V battery source into a resistive load of 24Ohm. The frequency of the chopper is set to 250Hz. When chopper on-time is 1 ms the load power is
A. 6W
B. 12W
C. 24W
D. 48W

 A thyristor half wave controlled converter has a supply voltage of 240V at 50Hz and a load resistance of 100 Ohm. when the firing delay angle is 30 the average value of load current is
A. 126A
B. 2.4A
C. 126mA
D. 24 A

 A full-wave fully controlled bridge has a highly inductive load with a resistance of 55 Ohm, and a supply of 110V at 50Hz. The value of load power for a firing angle α=75° is
A. 10W
B. 11W
C. 10.5W
D. 10.9W

 A D.C. to D.C. chopper operates from a 48 V source with a resistive load of 24Ohm. The chopper frequency is 250Hz. When Ton= 3 ms, the rms current is
A. 1.5A
B. 15mA
C. 1.73A
D. 173mA

 A 240V, 50Hz supply feeds a highly inductive load of 50 Ohm resistance through a thyristor full control bridge. when the firing angle α= 45°, load power is
A. 456 W
B. 466 W
C. 732 W
D. 120 W

 Thermal runaway is not possible in FET because as the temperature of FET increases
A. The mobility decreases
B. The transconductance increases
C. The drain current increases
D. None of the above

 The ripple frequency from a full wave rectifier is
A. twice that from a half wave circuit
B. the same as that from a half wave circuit
C. half that from a half wave circuit
D. 1/4 that from a half wave circuit

 In a full-wave rectifier using two ideal diodes,Vdc & Vm are the dc & peak values of the voltage respectively across a resistive loaD. If PIV is the peak inverse voltage of the diode,then the appropriate relationships for the rectifier is
A. Vdc=Vm/π,PIV=2Vm
B. Vdc=2Vm/π,PIV=2Vm
C. Vdc=2Vm/π,PIV=Vm
D. Vdc=Vm/π,PIV=Vm

 The output of a rectifier circuit without filter is
A. 50 Hz AC
B. smooth DC
C. pulsating DC
D. 60 hz AC 