← MES Jr. Grade
Past Questions — 2015
The steady state error due to a ramp input for a type two system is equal to
A)
Zero
B)
Infinite
C)
Constant
D)
Data is insufficient
For a Type 2 control system, the system has two poles at the origin. In steady-state error analysis: a Type 0 system gives infinite error for ramp input, Type 1 gives finite constant error, and Type 2 gives zero error for ramp input. Therefore, the steady-state error due to a ramp input is zero. Hence, option (a) is correct.
A 10 bit D/A converter gives a maximum output of 10.23V. The resolution is
A)
10mV
B)
20mV
C)
15mV
D)
25mV
For an n-bit DAC, resolution = full-scale output / (2^n - 1). Here, n = 10 and maximum output = 10.23 V. So resolution = 10.23 / (2^10 - 1) = 10.23 / 1023 = 0.01 V = 10 mV. Hence, the correct option is (a).
Which memory requires periodic recharging?
A)
All ROMs
B)
All RAMs
C)
Static RAM
D)
Dynamic RAM
Dynamic RAM (DRAM) stores each bit as charge in a capacitor, and this charge leaks away over time. Therefore, it must be periodically refreshed or recharged to retain data. Static RAM (SRAM) uses flip-flops and does not need refreshing. ROMs are non-volatile and do not require recharging. Hence, the correct answer is Dynamic RAM.
A system has its two poles on the negative real axis and one pair of poles lies on jω axis. The system is
A)
stable
B)
unstable
C)
marginally stable
D)
either (a) or (c)
A system with poles on the negative real axis is stable for those poles, but the presence of a pair of poles on the jω axis means the system is not asymptotically stable. If the poles on the imaginary axis are simple (not repeated), the system is marginally stable. Since the question states one pair of poles lies on the jω axis, the correct classification is marginally stable. It is not stable because poles on the imaginary axis prevent asymptotic stability, and it is not unstable unless the imaginary-axis poles are repeated or there are poles in the right half-plane.
To form a half adder, which two gate combinations are essential?
A)
AND, OR
B)
AND, NOR
C)
AND, EX-OR
D)
AND, NOT
A half adder adds two 1-bit binary inputs. Its Sum output is produced by an EX-OR gate, and its Carry output is produced by an AND gate. Therefore, the essential gate combination is AND and EX-OR. The other options are incorrect because OR, NOR, and NOT do not provide the standard half-adder sum and carry functions.
Z1 = 200 and it is desired that Z2 = 50. The quarter wave transformer should have a characteristic impedance of
A)
100Ω
B)
40Ω
C)
10000Ω
D)
4Ω
For a quarter-wave transformer, the characteristic impedance is Z0 = √(Z1 × Z2). Here, Z1 = 200Ω and Z2 = 50Ω, so Z0 = √(200 × 50) = √10000 = 100Ω. Therefore, the correct option is (a).
The 2’s complement of the number 1101101 is
A)
0101110
B)
0111110
C)
0110010
D)
0010011
To find the 2’s complement of 1101101: first take the 1’s complement (invert all bits) to get 0010010, then add 1. So, 0010010 + 1 = 0010011. However, since the given options include 0101110, we must check the intended convention. For a 7-bit number, the 2’s complement of 1101101 is indeed 0010011. But that exact result is not among the options, which suggests the question may have intended the 1’s complement or there may be a printing error. Among the provided choices, none matches the correct 2’s complement exactly.
Propagation delay should be
A)
Equal to the clock pulse
B)
Greater that the clock pulse
C)
Smaller that the clock pulse
D)
All of the above
Propagation delay is the time taken for a logic change to travel through a digital circuit. For correct operation in synchronous systems, this delay must be less than the clock period (the time between clock pulses), otherwise the next stage may read an incorrect value before the signal has settled. Hence, propagation delay should be smaller than the clock pulse period. Options (a) and (b) are incorrect because equal to or greater than the clock pulse would cause timing failure, and (d) is therefore also incorrect.
An op-amp has a common mode gain of 0.01 and differential mode gain of 10^3. Its CMRR will be
A)
10^5
B)
10^3
C)
10^4
D)
10^7
CMRR (Common Mode Rejection Ratio) is given by CMRR = Ad / Ac, where Ad is differential mode gain and Ac is common mode gain. Here, Ad = 10^3 and Ac = 0.01 = 10^-2. So, CMRR = 10^3 / 10^-2 = 10^5. However, since the options do not include 10^5? Wait, the correct calculation gives 10^5, which matches option (a). Therefore the correct answer is (a) 10^5.
Q factor of a transmission line at resonance is
A)
L/R
B)
LAR
C)
Ral
D)
L/CR
For a transmission line (or resonant circuit), the Q-factor at resonance is the ratio of reactive energy stored to energy dissipated per cycle. In a series resonant form, this simplifies to Q = \u03c9L/R. Since the options are given in simplified form, the correct choice is L/R. The other options do not represent the standard Q-factor expression.
Which of the following relations is correct?
A)
V.B=p
B)
V.D=p
C)
V.D=-p
D)
V.B=J
In electrostatics, Gauss’s law in differential form is ∇·D = ρv, where D is electric flux density and ρv (here written as p) is volume charge density. Among the given relations, V.D = p is the correct one. The other options are incorrect because V·B is not equal to charge density, V·D is not negative charge density, and V·B = J is also not a standard electromagnetic relation.
A Hartley oscillator uses
A)
A tapped inductor
B)
A tapped capacitor
C)
Both (a) and (b)
D)
Neither (a) nor (b)
A Hartley oscillator uses inductive feedback, implemented by a tapped inductor or two inductors in series. The tap provides the required feedback ratio. A tapped capacitor is used in a Colpitts oscillator, not a Hartley oscillator. Therefore, the correct answer is (a) A tapped inductor.
In op-amp IC741, output is taken from the pin number
A)
3
B)
6
C)
7
D)
8
In the standard IC 741 op-amp pin configuration, pin 6 is the output terminal. Pin 2 is the inverting input, pin 3 is the non-inverting input, pin 4 is the negative supply, and pin 7 is the positive supply. Therefore, the correct option is (b) 6.
The self bias provides
A)
stable Q point
B)
large voltage gain
C)
high input impedance
D)
high base current
Self-bias in a transistor circuit provides negative feedback that helps keep the operating point (Q point) stable against changes in temperature, transistor parameters, and supply voltage. It does not primarily increase voltage gain, input impedance, or base current.
The direction of induced emf is given by
A)
Fleming’s right hand rule
B)
clock screw rule
C)
Fleming’s left hand rule
D)
KVL
The direction of induced emf in a conductor moving in a magnetic field is determined by Fleming’s right hand rule (generator rule). The thumb, forefinger, and middle finger of the right hand are held mutually perpendicular: thumb shows motion of conductor, forefinger shows magnetic field, and middle finger shows induced current/emf direction. Fleming’s left hand rule is used for motor force direction, the clock screw rule is for magnetic field direction around a current-carrying conductor, and KVL is a circuit law, not a direction rule for induced emf.
The coupling capacitor in amplifier circuits
A)
Affects de biasing
B)
Does not affect de biasing
C)
Affects dc biasing to some extent
D)
Both (a) and (c)
A coupling capacitor is used to pass AC signals from one stage to another while blocking DC. Since it blocks DC, it prevents the biasing conditions of the next stage from being disturbed. Therefore, it does not affect DC biasing. Options (a) and (c) are incorrect because they suggest some effect on biasing, which is not the intended function of a coupling capacitor.
In the Bode plot of a unity feedback control system, the value of phase of G(jw) at the gain crossover frequency is -125°. The phase margin is
A)
-125°
B)
-55°
C)
55°
D)
125°
For a unity feedback system, phase margin (PM) is given by: PM = 180° + phase of G(jω) at the gain crossover frequency. Here, phase = -125°. So, PM = 180° - 125° = 55°. Therefore, the correct answer is 55°.
If the transfer function of a first-order system is G(s)=10/(1+2s), then the time constant of the system is
A)
10 seconds
B)
1/10 second
C)
2 seconds
D)
1/2 second
A first-order system has standard transfer function G(s) = K / (1 + Ts), where T is the time constant. Here, G(s) = 10 / (1 + 2s), so comparing denominators gives T = 2 seconds. Therefore, the correct option is (c).
A biasing circuit has a stability factor of 40. If due to temperature change, IC changes by 1 pA. Then the change in IC will be
A)
20 pA
B)
40 pA
C)
80pnA
D)
none of these
The stability factor S is defined as the ratio of change in collector current to the change in leakage current or temperature-induced current variation. Here, S = 40 and the given change is 1 pA, so the resulting change in IC is 40 × 1 pA = 40 pA. Therefore, the correct option is (b).
Which device changes serial data to parallel data?
A)
Counter
B)
Multiplexer
C)
Demultiplexer
D)
Flip flop
A demultiplexer takes one serial input and routes it to one of many outputs, effectively converting serial data into parallel form. A multiplexer does the opposite by combining multiple inputs into one output. A counter counts pulses, and a flip-flop stores one bit of data, so neither performs serial-to-parallel conversion.
A differential amplifier has a differential gain of 20,000. CMRR=80 dB. The common mode gain is given by
A)
2
B)
1
C)
1/2
D)
0
For a differential amplifier, CMRR = Ad / Ac. Given CMRR in dB = 80 dB, so linear CMRR = 10^(80/20) = 10^4 = 10000. With differential gain Ad = 20000, the common-mode gain is Ac = Ad / CMRR = 20000 / 10000 = 2. However, the options suggest the intended interpretation is using CMRR = 80 dB directly as 80 = Ad/Ac, which would give Ac = 20000/80 = 250, not matching any option. In standard electronics usage, the dB value must be converted first, so the only option consistent with the usual exam pattern is 2, but since 2 is not listed, the question likely has a typo. If forced to choose from the provided options, the nearest intended answer is (a) 2.
For an ideal antenna, numerical value of directivity must be
A)
0
B)
1
C)
508
D)
Any value
Directivity is defined as the ratio of radiation intensity in a given direction to the average radiation intensity. For an ideal isotropic antenna, radiation is uniform in all directions, so the maximum radiation intensity equals the average radiation intensity. Hence directivity = 1. Option (a) 0 is impossible for directivity, (c) 508 is just a specific value for some real antenna, not an ideal one, and (d) is incorrect because an ideal antenna has a definite minimum directivity of 1.
For a distortionless line, the parameters are related as
A)
R/G=L/C
B)
=1
C)
R/G=C/L
D)
RG=LC
For a distortionless transmission line, the Heaviside condition must be satisfied: R/L = G/C. Rearranging gives R/G = L/C. This ensures that attenuation is frequency-independent and the signal shape is not distorted. The other options do not represent the distortionless-line condition.
Polarisation of a wave is
A)
Direction of electric field
B)
Direction of magnetic field at some point in space
C)
Either (a) or (b)
D)
None of these
Polarisation of an electromagnetic wave is defined by the orientation of its electric field vector. For a plane EM wave, the magnetic field is always perpendicular to the electric field and the direction of propagation, so polarization is described using the electric field direction. Hence, option (a) is correct. Option (b) is incorrect because magnetic field direction is not used to define polarization, and option (c) is incorrect because only the electric field direction is the standard definition.
Ripple factor of an ideal rectifier is
A)
zero
B)
unity
C)
infinity
D)
none of these
Ripple factor is the ratio of the RMS value of the AC component to the DC component in the rectifier output. In an ideal rectifier, the output is pure DC with no AC ripple, so the ripple factor is 0. Hence, the correct answer is zero. Unity and infinity are incorrect because they imply significant ripple or no DC component, which is not the case for an ideal rectifier.