Power Semiconductor Devices and Their Applications MCQs

Question 1

In a.c. motor control, the ratio of voltage to frequency is maintanined at constant value

Accepted Answer

to make maximum use of magnetic circuit

Answer

to make minimum use of magnetic circuit

Answer

to maximise the current drawn from the supply to provide torque

Answer

to minimise the current drawn from the supply to provide torque

Question 2

A single-phase voltatge controller feeds an induction motor and a heater

Accepted Answer

In induction motor only fundamental and in heater harmonics as well as fundamental are useful

Answer

In both the loads only fundamental and harmonics are useful

Answer

In induction motor only fundamental and in heater only harmonics are useful

Answer

In induction motor only harmonics and in heater only fundamental are useful

Question 3

For type A chopper, Vs is the source voltage, R is the load resistance and a is the duty cycle. Average output voltage of this chopper is

Accepted Answer

aVs

Answer

(1 ? a) Vs

Answer

Vs/a

Answer

Vs/(1 ? a)

Question 4

With gate open, if the supply voltage exeeeds the breakover voltage of SCR, the SCR will conduct

Accepted Answer

true

Answer

false

Question 5

The SCR is turned-off when the anode current falls below

Accepted Answer

holding current

Answer

forward current rating

Answer

break-over voltage

Answer

latching current

Question 6

In a SCR circuit, the angle of conduction can be changed by changing

Accepted Answer

gate current

Answer

anode voltage

Answer

anode current

Answer

forward current rating

Question 7

The normal way to close a SCR is by appropriate

Accepted Answer

anode current

Answer

gate current

Answer

cathode current

Answer

forward current

Question 8

A SCR has __ PN junctions.

Accepted Answer

three

Answer

two

Answer

four

Answer

one

Question 9

If gate current is increased, the anode-cathode voltage at which SCR closes is

Accepted Answer

decreased

Answer

increased

Answer

maximum

Answer

least