381.
Permissible pH value of water for boilers is
A
10
B
1
C
7
D
slightly more than 7
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Permissible pH value of water for boilers is
10
1
7
slightly more than 7
The overall efficiency of a boiler in a thermal power plant is of the order of
70 to 80%.
10%
25 to 30%
40 to 50%
A Diac is a ................. switch
A mechanical
An c
none of the above
A dc
A diac is …………………. switch
A mechanical
An c.
None of the above
A d.c.
With increase in firing angle
Harmonic distortion decreases and quality of input current increases
Both harmonic distortion and quality of input current increases
Both harmonic distortion and quality of input current decreases
Harmonic distortion increases and quality of input current decreases
Which of the following is not a characteristic of UJT?
Peak-point voltage
Intrinsic stand off ratio
Bilateral conduction
Negative resistance
When the temperature increases, the intrinsic stand off ratio ....................
Essentially remains the same
Increases
None of the above
Decreases
When the temperature increases, the inter-base resistance (RBB) of a UJT ......................
Remains the same
Increases
None of the above
Decreases
When the emitter terminal of a UJT is open, the resistance between the base terminal is generally .......................
Extremely low
High
None of the above
Low
When a UJT is turned ON, the resistance between emitter terminal and lower base terminal.................................
Is increased
Remains the same
None of the above
Is decreased
Voltage commutation circuit can be converted into a current commutation by interchanging the positions of
Inductor and capacitor
Diode and capacitor
Capacitor and load
Capacitor and SCR
Very large values of modulation index (greater than 3.24 lead to)
Sine AC output voltage
Triangular AC output voltage
Square AC output voltage
Trapezoidal AC output voltage
Unipolar modulation is generally used in
AC - DC converters
DC - AC converters
AC - AC converters
DC - DC converters
Under harmonic free load voltages, the 3 phase VSI
Does not contains third harmonic
Does not contains fifth harmonic
Does not contains second harmonic
Does not contains seventh harmonic
TRIAC is a semiconductor power electronic device which contains
Two SCRs connected in parallel
Two SCRs connected in series
Two SCRs connected in reverse parallel
Two BJTs connected in series
To turn on UJT, the forward bias on the emitter diode should be ...................... the peak point voltage
Equal to
More than
Less than
None of the above
The V-I characteristics for a triac in the first and third quadrants are essentially identical to those of ........................ in its first quadrant
SCR
UJT
Transistor
none of the above
The UJT may be used as ............................
A sawtooth generator
A rectifier
Am amplifier
None of the above
The triac is .....................
A four-terminal device
Not a thyristor
Like a bidirectional SCR
Answers (1) and (2)
The switching function of semiconductor devices can be characterized with
Frequency only
Duty ratio and frequency
Duty ratio only
Duty ratio, frequency and time delay