ISBT Reasoning for all banking PO,Clerk,IBPS PO,Railway,SSC,IAS,OAS Exams

What is the time required to reach 2% of steady-state value, for the closed-loop transfer function 
2/ (s +10 )(s +100) , when the input is u(t) ?
1) 20s 2) 2s
3) 0.2s 4) 0.4s
5)None of these
Answer : 0.4s
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The open-loop transfer function of a unity feedback control system is 

G(s)H(s) = 10/ s (s+ 2)( s +K)

Here, K is a variable parameter. The system will be stable for all values of - 
1) K > – 2 2) K > 0
3) K > 1 4) K > 1.45
Answer : K > 1.45
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Which one of the following Analog-to-Digital Converters (ADC) does not use a DAC ?
1) Digital ramp ADC 2) Successive approximation ADC
3) Single-slope ADC 4) Counting ADC
5)None of these
Answer : Single-slope ADC
Explanation : Single-slope ADC (analog to digital converter) does not use DAC (digital to analog converter).
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A unit-step voltage is applied at t = 0 to a series R-L circuit with zero initial condition. Then ,which of following is/are correct ?
1) It is possible for the current to be oscillatory 2) The voltage across the resistor at t = 0+ is zero
3) The voltage across the resistor at t = 0 is zero 4) The resistor current eventually falls to zero
5)None of these
Answer : The voltage across the resistor at t = 0+ is zero
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A network in which all the elements are physically separable is called a - 
1) distributed network 2) lumped network
3) passive network 4) reactive network
5)None of these
Answer : lumped network
Explanation :
Distributed Network - In distributed network resistors, capacitors and inductors can not be electrically separated and individually isolated as separate elements. Ex-Transmission line.

Lumped Network - Lumped network in which physically separate resistors, capacitors and inductors can be represented.

Passive Network - Passive network contains the circuit elements without any energy source.

Reactive Network - Reacitve network contains L and C.
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A 3 -1/2 digit digital voltmeter is accurate to +_ 0.5% of reading +_ 2 digits. What is the percentage error, when the voltmeter reads 0.10 V on its 10V range ?
1) 0.025% 2) 0.25%
3) 2.05% 4) 20.5%
Answer : 20.5%
Explanation :
+_ 0.5 % of reading = (0.5/100) x 0.1= +_ 0.0005V
+_2 digit = +_0.02V
Total possible error = +_0.0205 V
The % error = (0.0205 100 /0.01) x 100  = 20.5%
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Which of the following are measured by using a vector voltmeter ?

1. Amplifier gain and phase shift
2. Filler transfer function
3. Complex insertion loss
Select the correct answer using the code given below :
1) 1 and 2 only 2) 1 and 3 only
3) 2 and 3 only 4) 1, 2 and 3
5)None of these
Answer : 1, 2 and 3
Explanation :
Vector voltmeter is an instrument which measure amplitude and phase of a signal. It uses two samplers to sample the two signals whose amplitude and relative phase are to be measured. It measures the voltages and phase difference at two different points to measure amplitude and phase difference. Vector voltmeter is used in the following measurements :
1. Complex insertion losses
2. Amplifier gain and phase shift
3. Filter transfer function
4. Complex impedance of mixers
5. ‘S’ parameters of transistors
6. Radio frequency distortions
7. Two-port network parameters
8. Amplitude modulation index.
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Which of the  following statements are correct ?

1. Metal conductors have more R at higher temperatures.
2. Tungsten can be used as a resistance wire.
3. A superconductive material is one which has practically zero resistance.
1) 1 and 2 only 2) 1 and 3 only
3) 2 and 3 only 4) 1, 2 and 3
5)None of these
Answer : 1 and 2 only
Explanation :
1. Metal conductors have more R at higher temperatures because of increased number of collisions between the free electrons and captive electrons.
2. Tungsten cannot be used as a resistance wire due to large variation of its resistance with increase in temperature.
3. Superconductive materials can conduct electricity or transport electrons from one atom to another with no resistance.
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Consider the following statements in connection with deflection-type and null-type instruments:
1. Null-type instruments are more accurate than the deflection-type ones.
2. Null-type of instrument can be highly sensitive compared to a deflection-type instrument.
3. Under dynamic conditions, null-type instruments are less preferred to deflection type instruments.
4. Response is faster in null-type instruments as compared to deflection-type instruments.

Which of the above statements are correct ?

1) 1, 2 and 3 2) 1, 2 and 4
3) 1, 3 and 4 4) 2, 3 and 4
5)None of these
Answer : 1, 2 and 3
Explanation :
Null-type instruments are more accurate than the deflection-type. It is because the opposing effect is calibrated with the help of standards which have high degree of accuracy. But, in the deflection type instrument, accuracy is dependent upon their calibration which depends upon the instrument constants which have not very high accuracy.

Null-type instrument can be highly sensitive compared to deflection type because in null type instrument, the detector has to cover a small range around the null point. Further, the detector need not be calibrated since it has only to detect the presence and direction of unbalance and not the magnitude of unbalance.

Null-type instruments are less preferred than deflection-type instrument under dynamic
condition because null-type instruments equire many changes before reaching null condition. But deflection-type instruments can follow the variations of measurement more rapidly.
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A voltmeter having a sensitivity of 1000 omega/V reads 100 V on its 150 V scale when connected across at resistor of unidentified specifications in series with a milli-ammeter. When the milli-ammeter reads 5 mA, the error due to the loading effect of the voltmeter will be nearly - 

1) 13% 2) 18%
3) 23% 4) 33%
5)None of these
Answer : 13%
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