INDIAN SPACE & RESEARCH ORGANIZATION
ISRO Exam Papers
Electronics & Communication
Q.1.In the given circuit the voltage Vc across C at time t = ∞ is- 5
- 10 V
- 20 V
- zero
- LR
- L/R
- L2R
- LR2
- R decreases
- R increase
- impedance increases
- voltage increases
- Transformer
- Silicon controlled rectifier
- Electron bulb
- Loud-speaker.
- Aluminium
- Boron
- Phosphorus
- Indium
- 0.12 eV
- 1.12 eV
- 0.72 eV
- 0.92 eV
- first band
- second band
- third band
- conduction band
- tunnel diode
- zener diode
- photo emissive diode
- photo sensitive diode
- 278 * 1011 cm-3
- 2.78 * 109 cm3
- 2.78 * 10-2 cm3
- 2.78 * 1019 cm3
- NPN transistor
- FET
- UJT
- MOSFET
- IC / IE (Ans)
- IC / IS
- IB / IE
- IB / IC
- 1
- 2
- 3
- 4 (Ans)
- 0
- 1
- 2
- 3
- 0.5
- 5
- 0.2
- 2
- 30 Hz
- 300 Hz
- 0.3 p Hz
- 100 Hz
16. In which of the following applications vacuum tubes are still being used ?
(A) public address system
(B) radio receivers
(C) radio transmitters (Ans)
(D) electroplating plants
17. Transistors have not replaced vacuum tubes because
(A) transistors are non-linear
(B) transistors do not have grid
(C) high power transistors are not available (Ans)
(D) heat dissipation from transistors is difficult
18. The value of L needed with C of 20 pF for an oscillator frequency of 110.7 MHz, is
(A) 0.32 μH (Ans)
(B) 0.5 μH
(C) 1 μH
(D) 5 μH
Hints and Solutions : ∵ fr = 1/2p √LC
So, L = 1/4pC fr2
= 1012/4 * 3.14 * 20 * (110.7)2 * 1012 = 0.32 μH
19. A Wein bridge oscillator has R1 = R2 = 220 kΩ and C1 = C2 = 250 pF. The frequency of oscillations will be nearly
(A) 0.89 kHz
(B) 1.89 kHz
(C) 2.89 kHz (Ans)
(D) 3.89 kHz
Hints and Solutions : f = 1/2p RC
= 1012/2 * 3.14 * 220 * 103 * 250 = 2.89 kHz
20. RC network shown in Fig. is used in a low frequency oscillator circuit. The frequency of oscillations will be
(A) 1.59 kHz
(B) 15.9 kHz (Ans)
(C) 159 kHz
(D) 1590 kHz
Hints and Solutions : f = 1/2p RC = 1/2 * 3.14 * 105 * 10-10
= 105/2 * 3.14 = 15.9 kHz.
21. Demodulation
(A) is performed at the transmitting station
(B) removes side bands
(C) rectifies modulated signal
(D) is opposite of modulation (Ans)
22. A frequency multiplier stage should operate as
(A) Class A
(B) Class B
(C) Class C (Ans)
(D) Either of the above
23. Pulse modulation is used in
(A) radio navigation
(B) automatic landing equipment
(C) data communication
(D) all of the above (Ans)
24. Which of the following modulating system is digital ?
(A) PPM
(B) PWM
(C) PCM (Ans)
(D) PEM
25. A 360 W carrier is simultaneously modulated by two audio waves with modulation percentage of 55 and 65 respectively. The total side band power radiated will be
(A) 180 watts
(B) 130 watts (Ans)
(C) 60 watts
(D) 30 watts
26. A radio transmitter, amplitude modulated radiates 50 kW of carrier power. The radiated power at 85% modulation will be
(A) 50.85 kW
(B) 51.7 kW
(C) 59.9 kW
(D) 68.1 kW (Ans)
27. For a FM wave carrier modulating frequency is 10 kHz and band-width is 2 MHz. If the modulating signal amplitude is doubled, the band width will be
(A) 0.5 MHz
(B) 1 MHz
(C) 2 MHz
(D) 4 MHz (Ans)
28. The balanced modulator circuit uses -
(A) two identical diodes
(B) two identical triodes (Ans)
(C) two diodes with different V-I characteristics
(D) two triodes with different V-I characteristics
29. To observe a portion of a wave form we must use
(A) free-running oscilloscope
(B) triggered-sweep oscilloscope (Ans)
(C) vector scope
(D) cathode ray tube
30. An oscilloscope is generally used to measure the value of
(A) dc voltage
(B) rms, ac voltage
(C) peak to peak ac voltage (Ans)
(D) average value of ac voltage
31. The purpose of a syne control in an oscilloscope is to
(A) set the intensity level
(B) control brightness
(C) set the focus
(D) lock the signal (Ans)
32. The length of the sweep on the CRT screen controlled by
(A) syne control
(B) sweep selector
(C) horizontal gain (Ans)
(D) vertical gain
33. Ionoscope is based on
(A) photo emission (Ans)
(B) secondary emission
(C) photo voltic effect
(D) photo conducting principle
34. A capacitor of capacitance c1 and distance between the plate is d1. A second capacitor of capacitance c2 and distance between the plate is d2.
When they are connected to series what is the equivalent capacitance ?
(A) d1d2 / d1 + d2
(B) d1 + d2 / d1d2
(C) c1 + c2
(D) c1 * c2 / c1 + c2 (Ans)
Hints and Solutions : Ceq = C1 C2 / C1 + C2
35. In a circuit voltage in the inductor is 2 V and inductance of the inductor is 1 mH. What is the rate of the current decay ?
(A) 2A/S
(B) 1 * 103 A/S
(C) 2 * 103 A/S (Ans)
(D) none of these
Hints and Solutions : VL = L di/dt
36. In a circuit current passing the capacitor is 1A. The capacitance of the capacitor is 1 μF. Find the voltage decay of the capacitor ?
(A) 1 V/S
(B) 1 * 106 V/S (Ans)
(C) 2 * 103 V/S
(D) none of these
Hints and Solutions : i = C dvc / dt
dvc / dt = i / C = 1/1 * 10-6 = 106 Volt / sec.
37. Two capacitors are connected in series. The first capacitor is of capacitance 40 μF and breakdown voltage 60 V and capacitance of second capacitor is 60 μF and break down voltage is 40 V. What condition is satisfied ?
(A) First capacitor break down is first
(B) Second capacitor break down is first
(C) The charge equal to the both capacitor (Ans)
(D) None of these
38. What is3the state equation for the nth order of differential equation,
(A) n
(B) (n + 1) (Ans)
(C) (n + 1) / 2
(D) (n - 1)2
39. Precision measurement of resistance is generally carried out by
(A) Potentiometer method
(B) CRO method
(C) Voltmeter-ammeter method
(D) Bridge method (Ans)
Q.40.The average power flow per unit area in a uniform plane wave in an electric field of maximum voltage E0 and impedance Z0 is
- E02 / 2Z0
- E02 / Z0
- E02 / Z02
- I0 E0