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BSNL Previous Year Paper
1. In a cylindrical cavity resonator, the two modes which are degenerate would include
a. TE111 and TM111
b. TE011 and TM011
c. TE022 and TM111
d. TE111 and TM011
2. When an antenna of input resistance 73 ohm is connected to a 50-ohm line and if the losses are ignored then it's efficiency will be nearly
a. 0.19
b. 0.81
c. 0.97
d. 1.19
3. If an isolated conducting sphere in air has radius = 1/ 4pqe0 it capacitance will be
a. Zero
b. IF
c. 4pF
d. OF
4. When a dominant mode wave guide not terminated in it's characteristic impedance is excited with a 10 GHz signal then if 'd' is the distance between two successive minima of the standing wave in the guide then
a. d = 1.5 cm
b. d is less then 1.5 cm
c. d is greater than 1.5 cm
d. d = 3cm
5. When a dipole antenna of l/8 length has an equivalent total loss resistance of 1.5 W -then the efficiency of the antenna is
a. 0.89159 %
b. 8.9159 %
c. 89.159 %
d. 891.59 %
6. In commercial FM broadcasting, the maximum frequency deviation is normally
a. 5 KHz
b. 15 KHz
c. 75 KHz
d. 200 KHz
7. Weins bridge is used for measurement of frequency in the applied voltage waveform is measurement of frequency in the applied voltage waveform is
a. sinusoidal
b. square
c. rectangular
d. triangular
8. Strain gauge is
a. not a transducer
b. an active transducer
c. not an electronic instrument
d. none
9. A high Q coil has
a. large band width
b. high losses
c. low losses
d. flat response
10. In the case of an instrument reading of 8.3V with a 0 to 150 voltmeter having a guaranteed accuracy of 1% full scale reading, the percentage limiting error is
a. 1.810%
b. 0.181%
c. 18.10%
d. 0.0018%
11. The 'h' parameter equivalent circuit of a junction transistor is valid for
a. High frequency, large signal operation
b. High frequency, small signal operation
c. Low frequency, small signal operation
d. Low frequency, large signal operation
12. A system is causal if the output of any time depends only on-
a. Values of input in the past and in the future
b. Values of input at that time and in the past
c. Values of input at that tim
e and in the future
d. None
13. A iron cored choke is a
a. Linear and active device
b. Non linear and passive device
c. Active device only
d. Linear device only
14. Pointing vector wattmeter uses
a. Seebeck effect
b. Ferranti effect
c. Induction effect
d. Hall effect
15. Which one of the following is not a transducer in the true sense ?
a. Thermocouple
b. Piezoelectric pick-up
c. Photo voltaic cell
d. LCD
16. The term used to denote a static device that converts ac to dc, dc to ac, dc to dc or ac to ac is
a. Converter system
b. Inverter
c. Chopper
d. Thyristor
17. It is a unidirectional device that blocks the current flow from cathode to anode
a. SCR
b. PCR
c. VCR
d. DCR
18. An ideal constant current source is connected in series with an ideal constant voltage source. Considering together the combination will be a
a. constant voltage source
b. constant current source
c. constant voltage and a constant current source or a constant power source
d. resistance
19. Anode current in an thyristor is made up of
a. electrons only
b. electrons or holes
c. electrons and holes
d. holes only
20. For a pulse transformer, the material used for its core and the possible turn ratio from primary to secondary are respectively
a. ferrite: 20: 1
b. laminated iron: 1: 1
c. ferrite: 1: 1
d. powdered iron: 1: 1
21. A converter which can operate in both 3 pulse and 6 pulse modes is a
a. 1 phase full converter
b. 3 phase half wave converter
c. 3 phase semi converter
d. 3 phase full converter
22. A single phase CSI has capacitor C as the load. For a constant source current, the voltage across the capacitor is
a. square wave
b. triangular wave
c. step function
d. pulsed wave
23. A single phase full wave midpoint thyristor converter uses a 230/200V transformer with center tap on the secondary side. The P.I.V per thyristor is
a. 100V
b. 141.4V
c. 200V
d. 282.8V
24. In dc choppers for chopping period T, the output voltage can be controlled by FM by varying
a. T keeping Ton constant
b. Ton keeping T constant
c. Toff keeping T constant
d. None of the above
25. From the hot metal surface electrons escape because
a. of change of state from metal to gas due to heat.
b. of change of stats from gas to metal.
c. the energy supplied is greater than the work function
d. the energy is greater than Fermi level.
26. The most common device used for detection in radio receivers is -
a. amplifier
b. triode
c. diode
d. transistor
27. In a full wave rectifier the negative point in a circuit is
a. Either cathode
b. Either anode
c. The central tap on the high voltage secondary
d. Either plate
28. Negative feedback amplifier has a signal corrupted by noise as its input. The amplifier will
a. Amplify the noise as much as the signal
b. Reduce the noise
c. Increase the noise
d. Not effect the noise
29. Match the given feedback circuit with it's proper nomenclatures
a. Current series feedback
b. Current shunt feedback
c. Voltage series feedback
d. Voltage shunt feedback
30. Class A amplifier is used when
a. No phase inversion is required
b. Highest voltage gain is required
c. dc voltages are to be amplified
d. Minimum distortion is desired
