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ISRO Technical Assistant Paper


Q1 The number 149 in octal code is

(a) 154   (b) 178   (c) 254    (d) 225

Ans(d)- 225

Q2 In full adder, there are

(a) Two binary number inputs and two outpurs

(b) Three binary digit inputs and two binary outputs

(c) Three binary digit inputs and three binarydigit outputs

(d) NAND & OR gates

three input Cin,2 input & 2 output Sum,Carry

Q3 Universal gates are

(a) OR & AND gates

(b) NOR & AND gates
(c) NOR & NAND gates
(d) NAND & OR gates

Ans(c)- NAND & NOR are Universal gate be cause by using these gates we can make any basic gate like AND,OR,NOT also arithmetic gates like X-OR & X-NOR

Q4 The main advantage of PCM system is lower

(a) bandwidth  (b) power

(c) noise             (d) none of these

PCM is more noise resistant among any other modulation like AM,FM,PM,DSBSC,SSB,VSB,PAM,PWM,PPM.

Q5 To transmit N signals each band limited to fm Hz by time division multiplexing will require a minimum bandwidth of

(a) fm      (b) 2fm

(c) Nfm    (d) fm/N

TDM minimum bandwidth required is Nfm.

Q6 Automatic gain control is used

(a) To maintain the tuning correct

(b) To reduce the volume of loud passages of music

(c) To increase the amplification at high frequencics

(d) To maintain the same volume of output when stations of different strength are received

Automatic gain control is used to maintain minimum stregth power to detect signal where strength of signal is varied

Q7 Using negative feedback for
improvements, which statement is false

(a) Increased bandwidth

(b) Increased noise
(c) Decreased distortion
(d) High input impedance but lower output impedance

By negative feedback Input impedence,Bandwidth, sensitivity increase & Gain,output impedence,noise, distortion decrease

Q8 In a current transformers

(a) the number of turns in primary and secondary windings are nearly equal

(b) the number of primary turns is
very small as compared to number of secondary turns

(c) the number of secondary turns
is very small as compared to the number of primary turns
(d) either (a) or (c).

the number of primary turns is very small as compared to number of secondary turns

Q9 For a base current of 10 uA, What is the value of collector current in common emitter if Bc 100

(a) 10uA       (b) 100uA

(c) 1mA        (d) 10mA


Q10 The turn ratio of a transformer is 20:1, if a load of 100 is connected across the secondary, what will be the effective resistance seen looking into the Primary?

(a) 2 kohm       (b) 4 kohm

(c) 8 kohm       (d) 32 kohm

Ans(b)- 4 kohm

Q11 Which statement is correct?

(a) BJT and MOSFET are current controlled devices

(b) BJT is voltage controlled and
MOSFET is current controlled device

(c) BJT and MOSFET are voltage controlled devices

(d) BJT is current controlled and
MOSFET is voltage controlled device

BJT ouput current is control by input current & In Mosfet output current is control by input gate voltage

Q12 To satisfy the sampling theorem, a 100 Hz sine wave should be sampled at

(a) 10 Hz       (b) 100 Hz

(c) 200 Hz     (d) 50 Hz

Ans(c)- Minimum sampling frequency 2fm= 2*100 = 200 Hz

Q13 In junction transistor,
recombination of electrons and holes occurs in

(a) base region only

(b) emitter region only
(c) collector region only
(d) all the 3 regions

Ans(d)- all 3 regions

Q14 How many FF are required to build a binary counter circuit to count from 0 to 1023

(a) 1  (b) 6   (c) 10   (d) 24

No of Count <= 2^N
where N is no of flip-flop

Q15 In a sequential circuit,
the outputs at any instant of time depends

(a) only on the inputs present at that instant of time

(b) on past outputs as well as present inputs

(c) only on the past inputs

(d) only on the present outputs

On past outputs as well as present inputs

Q16 The address bus width of a memory of size 1024 x 8 bits is

(a) 10 bits         (b) 8 bits

(c) 13 bits         (d) 18 bits

Memory Size = 2^A*D
where A is address line & D data lines

Q17 The number of
comparators in a parallel conversion type 8-bit A to D converter is

(a) 8  (b) 16   (c) 255   (d) 127

Ans(c)- 255

Q18 the frequency deviation produced in a VHF carrier by a signal of 100 Hz is 50 kHZ. 
frequency modulation index is

(a) 100 radians     (b) 250 radians

(c) 500 radians      (d) 750 radius

Ans(c)- 500 radians

Q19 An analog voltage is in the range of 0 to 8 V is divided in eight equal intervals for conversion to 3-bit digital output. The
maximum quantization error is

(a) 0 V       (b) 0.5 V
(c) 1 V       (d) 2 V

Maximum quantization error is = (step size)/2
step size = Vmax/2^N
where N is no of Bit

Q20 In NPN transistor, when emitter junctions forward biased and collector junction is reverse bias, the transistor will operate in

(a) Active region  
(b) Saturation region
(c) Cut off region
(d) Inverted region

Active Mode = Emitter-Base Forward biase & Collector-Base Reverse Bias
Saturation Mode = Emitter & Collector both forward Bias
Cutt off Mode = Both Emitter & Collector Reverse Biased
Inverting Mode = Emitter Reverse & Collector Forward Bias

Q21 How many cascaded stages of CE amplifiers will result in polarity inversion of the input signal?

(a) Two        (b) Three
(c)  Four       (d)  None

Even no of Cascaded stages give same output as input while Odd no of Cascaded stages gives polarity inversion because single stage give 180 degree changes in the output.

Q22 A FET has

(a) very high input resistance
(b) very low input resistance
(c) high voltage emitter junction
(d) forward bias PN Junction

FET has very high input Impedence because Input Gate is reversed biased

Q23 A triac is a semi-conductor device which acts as a

(a) 2 Terminal unidirectional switch

(b) 2 Terminal bidirectional switch

(c) 3 Terminal bidirectional switch

(d) 4 terminal multi-directional switch

3-Terminal Anode,Cathode & Gate
TRIAC is Bidirectional which conduct in both half cycle of AC.

Q24 A junction Field Effect Transistor can operate in

(a) depletion mode only
(b) enhancement mode only
(c) depletion and enhancement modes
(d) neither depletion nor enhancement modes

Ans(a)- Depletion Mode only

Q25 An amplifier should have

(a) High fidelity

(b) Low noise
(c) Stable operation
(d) All of the above

Opamp have all features

Q26 The form factor in reference to alternating current wave form represents the ratio of

(a) the average value to the RMS value

(b) the peak value of the RMS value

(c) the RMS value to the average value

(d) the RMS value to the peak value

Form Factor = RMS/Avg
Peak Factor = Peak/RMS

Q27 Which of the following is the fastest switching device?

(a) JFET            (b) BJT
(c) MOSFET     (d) Triode

Fastest Switching device Mosfet
while highest frequency device BJT

(a) transformer coupling
(b) resistance coupling
(c) impedance coupling
(d) capacitance coupling

transformer Coupling-Highest gain
Direct Coupling-Lowest Gain

Q29 What suits best for a Hartley oscillator circuit?

(a) a Capacitor for feedback
(b) resistor and capacitor for feedback
(c) a tapped capacitor and inductor for feedback
(d) a tapped inductor for inductive feedback

Inductor in Hartley & Capacitor in Colpit Oscillator is used for feedback

Q30 A pulse transformer uses

(a) ferrite core     (b) iron core
(c) air core            (d) copper core

Ans(a)- ferrite core

Q31 If across an ideal resistor, the voltage drop is 24 V and the current passing through it is 6, then the resistor value (in ohms) is

(a) 144         (b) 4
(c) 0.25        (d) none of the above

V=IR   then R = 24/6 = 4 ohm

Q32 In microprocessors, the OC (instruction cycle), FC (fetch cycle) and EC (execution cycle) are related as

(a) IC=FC+EC
(b) IC-FC+EC
(c) FC=IC+EC
(d) EC=IC+FC

Instruction Cycle = Fatch Cycle + Execution Cycle

Q33 How many Flip flops circuits are needed to divide by 16?

(a) Two          (b) Four
(c) Eight         (d) Sixteen

Each flip-flop divide by 2 so to divide by 16 we need 4 flip-flop.

Q34 In 8085 microprocessor, initially the number decimal 8 is stored. If instruction RAL is executed twice on this number, the final number stored will be

(a) decimal 8        (b) decimal 80
(c) decimal 32      (d) decimal 2

RAL instruction executed 1 times will multiply by 2 & if it executed twice it multiply by 4 so it will be 32

Q35 A 256 x 4 EPROM has

(a) 8 address pins and 2 data pins
(b) 8 address pins and 4 data pins
(c) 8 address pins and 8 data pins
(d) 256 address pins and 4 data pins

( 2^A)*D,  A=address pin, D=data

Q36 The resolution of a dual slope ADC can be increased by

(a) Increasing the reference voltage magnitude
(b) Improving the reference voltage accuracy
(c) Increasing the clock frequency
(d) Increasing the clock stability

Resolution = Vrefrence voltage/ 2^N

Q37 The rotor of an induction motor cannot run with synchronous speed because

(a) Lenz’s law will be violated
(b) Rotor torque will then be zero
(c) Induction motor would become synchronous motor
(d) Air function prevents it to do so

Lenz’s law will be violated



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