Company: Bharat Sanchar Nigam Ltd

BSNL Junior Telecom Officers (JTO) Examination Exam Paper 2005

Thyristor A has rated gate current of 2A and thyristor B a rated gate current of 100 mA-
a) A is a GTO and B is a conventional SCR
b) B is a GTO and A is a conventional SCR
c) B may operate as a transistor
d) none of the above
Answer: a)

In a 3 phase full converter, the output voltage during overlap is equal to-
a) zero
b) source voltage
c) source voltage minus the inductance drop
d) average value of the conducting phase voltages
Answer: d)

Mark old the correct statement for Cycloconverters-
a) step-down Cycloconverter (CC) works on natural commutation
b) step up CC requires no forced commutation
c) load commutated CC works on line commutation
d) none of the above
Answer: a)

In a 3 phase full converter if load current is I and ripple free, then average thyristor current is-
Answer: b)1/3(I)

In the RF amplifier stage cascade (CE-CB) amplifier is used because it gives-
a) Large voltage gain
b) Low output impedance
c) Large isolation between the input and the output
d) None of the above
Answer: c)

Silicon diode is less suited for low voltage rectifier operation because-
a) it can withstand high temperature
b) ensures low PIV of the diodes
c) ensures lower values of capacitance in the filter
d) reduces ripple content
Answer: a)

An amplifier of class A is that in which –
a) Base is biased to cut ? off
b) Ic flows most of the time
c) Ie flows all the time
d) Vc often raises to Vcc
Answer: c)

A transistor is in active region when-
a) IB = bIC
b) IC=bIB
c) IC=IE
d) IC=IB
Answer: a)

For coupling purposes in RF amplifier a buffer amplifier is used because it provides-
a) Maximum loading and minimum mismatch
b) Minimum loading and minimum mismatch
c) Maximum loading and maximum mismatch
d) Minimum loading and maximum mismatch
Answer: b)

A transistor has CE parameter as hie = 10kW, hre =20 x 10-4 , hse = 100, hoe = 25 ms. The hib for this transistor will be-
a) 100 W
b) 99.01 W
c) 5m W
d) 101kW
Answer: b)

An FM radio receiver is tuned to a 90.6 MHz broadcast station. It will receive an image frequency of –
a) 110 MHz
b) 112 Hz
c) 114 MHz
d) 120 MHz
Answer: b)

In the given fig RL is shorted out, then VCE will become-

a) OV
c) Equal to VCC
d) None of the above
Answer c)

See the circuit shown and choose the correct option ?

a) Only red will glow
b) Only green will glow
c) Both red and green will glow
d) Neither red nor green will glow
Answer: a)

A dc to dc converter having an efficiency of 80% is delivering 16W to a load) If the converter is generating an output of 200V from an input source of 20V, then the current drawn from the source will be ?
a) 0.1A
b) 0.5A
c) 1.0A
d) 10.0A
Answer: c)

A transistor is operated as a non-saturated switch to eliminate ?
a) storage time
b) turn ? off time
c) turn ? on time
d) delay time
Answer: b)

The output Y of the circuit in the given figure is ?

a) (A + B)C + DE
b) AB + C(D + E)
c) (A + B)C + D + E
d) (AB + C) . DE
Answer: a)
Rotors used in a two-phase ac servomotor is ?
a) solid iron motor
b) squirrel cage rotor
c) drag cup rotor
d) both b and c
Answer: d)