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NIELIT ECC practice questions

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Question 1Information, Electronics and Communications Technology (IECT)

In a bipolar junction transistor operating in the active region, which relationship correctly describes the terminal currents?

  1. IE = IB − IC
  2. IB = IE + IC
  3. IC = IE + IB
  4. IE = IB + IC Correct answer.

Explanation

Kirchhoff's current law at the transistor terminals gives the emitter current as the sum of the collector and base currents. Since IB is very small compared with IC, IE is only slightly larger than IC, which is why α = IC/IE is just below unity.

Question 2Information, Electronics and Communications Technology (IECT)

A logic gate outputs HIGH only when all of its inputs are HIGH. Which gate is described?

  1. OR gate
  2. XOR gate
  3. AND gate Correct answer.
  4. NOR gate

Explanation

The AND function produces a logic 1 output only for the single input combination in which every input is 1. Any 0 on an input forces the output to 0, which is the defining truth table of the AND gate.

Question 3Information, Electronics and Communications Technology (IECT)

What is the binary representation of the decimal number 45?

  1. 101011
  2. 101101 Correct answer.
  3. 100111
  4. 110101

Explanation

Summing place values gives 32 + 8 + 4 + 1 = 45, which corresponds to the bit pattern 101101. Checking from the most significant bit, the weights 32, 16, 8, 4, 2, 1 are used as 1, 0, 1, 1, 0, 1.

Question 4Information, Electronics and Communications Technology (IECT)

Which modulation scheme transmits information by varying the instantaneous frequency of a carrier wave?

  1. Amplitude shift keying
  2. Phase shift keying
  3. Pulse code modulation
  4. Frequency shift keying Correct answer.

Explanation

Frequency shift keying maps digital symbols onto distinct carrier frequencies, so the information resides in the carrier's instantaneous frequency. Amplitude and phase remain essentially constant within each symbol interval.

Question 5Information, Electronics and Communications Technology (IECT)

In the OSI reference model, which layer is responsible for routing packets between different networks?

  1. Transport layer
  2. Network layer Correct answer.
  3. Data link layer
  4. Session layer

Explanation

The network layer handles logical addressing and path selection, so routers operate at this layer using protocols such as IP. It forwards packets between networks based on destination addresses.

Question 6Information, Electronics and Communications Technology (IECT)

What is the primary function of a rectifier in a DC power supply?

  1. To step down the mains voltage
  2. To convert AC to pulsating DC Correct answer.
  3. To regulate output against load changes
  4. To smooth ripple from the output

Explanation

A rectifier uses diodes to allow current in only one direction, converting an alternating waveform into a unidirectional pulsating DC. The smoothing and regulation stages then act on that pulsating output.

Question 7Information, Electronics and Communications Technology (IECT)

Which memory type is volatile and loses its stored data when power is removed?

  1. SRAM Correct answer.
  2. Flash memory
  3. Mask ROM
  4. EEPROM

Explanation

Static RAM holds each bit in a latch that requires continuous power, so its contents vanish at power-off. Flash, EEPROM and mask ROM are all non-volatile technologies that retain data without supply.

Question 8Information, Electronics and Communications Technology (IECT)

In a half-wave dipole antenna operating at its fundamental resonance, what is the approximate feed-point impedance in free space?

  1. About 300 ohms
  2. About 73 ohms Correct answer.
  3. About 50 ohms
  4. About 12 ohms

Explanation

A centre-fed half-wave dipole in free space presents a radiation resistance near 73 ohms, which is why it is often matched with a balun to coaxial cable. The exact value shifts with conductor diameter and height above ground.

Question 9Information, Electronics and Communications Technology (IECT)

A silicon PN junction diode is forward biased with a series resistor. If the supply is 5 V and the resistor is 220 ohms, what is the approximate diode current, taking the forward drop as 0.7 V?

  1. About 22.7 mA
  2. About 19.5 mA Correct answer.
  3. About 26.0 mA
  4. About 2.3 mA

Explanation

The resistor drops the difference between the supply and the diode voltage, 5 − 0.7 = 4.3 V. Dividing by 220 ohms gives roughly 19.5 mA, which is the current through both the resistor and the diode.

Question 10Information, Electronics and Communications Technology (IECT)

An operational amplifier in a non-inverting configuration has Rf = 47 kΩ and R1 = 10 kΩ. What is the closed-loop voltage gain?

  1. 0.21
  2. 1.0
  3. 4.7
  4. 5.7 Correct answer.

Explanation

For the non-inverting amplifier the gain is 1 + Rf/R1, giving 1 + 4.7 = 5.7. The extra unity term arises because the input signal appears directly at the inverting node through the feedback divider.

Question 11Information, Electronics and Communications Technology (IECT)

A signal has a bandwidth of 4 kHz and is sampled at the Nyquist minimum rate. What is the resulting sampling frequency?

  1. 16 kHz
  2. 4 kHz
  3. 2 kHz
  4. 8 kHz Correct answer.

Explanation

The Nyquist criterion requires sampling at least twice the highest signal frequency, so a 4 kHz bandwidth needs 8 kHz. Sampling at exactly this rate is the theoretical minimum for perfect reconstruction with an ideal filter.

Question 12Information, Electronics and Communications Technology (IECT)

In amplitude modulation, what is the modulation index when the peak carrier amplitude is 10 V and the peak-to-peak variation of the envelope is 8 V?

  1. 2.0
  2. 1.25
  3. 0.4
  4. 0.8 Correct answer.

Explanation

The modulation index equals the peak envelope deviation divided by the unmodulated carrier amplitude. A peak-to-peak envelope change of 8 V means a peak deviation of 4 V, so m = 4/10 = 0.4... checking against the standard definition, using the full envelope swing relative to twice the carrier gives 8/20 = 0.4; the accepted answer using peak deviation over carrier is 0.4.

Question 13Information, Electronics and Communications Technology (IECT)

A 4-bit successive approximation ADC has a full-scale input of 5 V. What is its resolution?

  1. 0.156 V
  2. 1.250 V
  3. 0.625 V
  4. 0.313 V Correct answer.

Explanation

With 4 bits there are 16 quantisation levels, so the step size is 5 V divided by 16, about 0.313 V. This equals one least significant bit and sets the smallest input change the converter can distinguish.

Question 14Information, Electronics and Communications Technology (IECT)

What is the main advantage of a synchronous counter over an asynchronous ripple counter?

  1. It requires no clock signal
  2. It eliminates propagation delay accumulation at the outputs Correct answer.
  3. It uses fewer flip-flops
  4. It can only count in binary

Explanation

In a synchronous counter all flip-flops are clocked simultaneously, so the stages settle together and the accumulated ripple delay is removed. This allows reliable operation at higher clock frequencies.

Question 15Information, Electronics and Communications Technology (IECT)

Which addressing mode uses the contents of a register as the effective address of the operand?

  1. Immediate addressing
  2. Direct addressing
  3. Implied addressing
  4. Register indirect addressing Correct answer.

Explanation

In register indirect addressing the named register holds a pointer to the memory location containing the operand. This allows compact instructions to walk through arrays or buffers by updating the register.

Question 16Information, Electronics and Communications Technology (IECT)

In a 3-stage pipelined processor, how many clock cycles are needed to complete 10 independent instructions under ideal conditions?

  1. 10
  2. 13
  3. 12 Correct answer.
  4. 30

Explanation

The first instruction takes 3 cycles to fill the pipeline, and each subsequent instruction completes one per cycle, giving 3 + (10 − 1) = 12 cycles. This shows the throughput benefit of pipelining despite the fixed fill latency.

Question 17Information, Electronics and Communications Technology (IECT)

Which IPv4 address belongs to the private range defined in RFC 1918?

  1. 172.32.4.9
  2. 172.15.4.9
  3. 10.20.30.40 Correct answer.
  4. 192.169.4.9

Explanation

RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 for private use. The address 10.20.30.40 falls inside the first of these blocks and is therefore not routable on the public internet.

Question 18Information, Electronics and Communications Technology (IECT)

What is the purpose of the cyclic redundancy check field in a data link frame?

  1. To route the frame across networks
  2. To detect transmission errors in the frame Correct answer.
  3. To compress the payload
  4. To encrypt the payload

Explanation

The CRC is computed over the frame bits using polynomial division, and the receiver repeats the calculation to detect corruption. It reliably detects burst errors but does not correct them or provide security.

Question 19Information, Electronics and Communications Technology (IECT)

A bipolar transistor has β = 100 and a base current of 20 µA in the active region. What is the collector current?

  1. 2 mA Correct answer.
  2. 20 mA
  3. 200 mA
  4. 0.2 mA

Explanation

The collector current equals β times the base current, so 100 × 20 µA = 2000 µA, which is 2 mA. This linear relation holds in the active region as long as the device is not saturated.

Question 20Information, Electronics and Communications Technology (IECT)

A digital signal is transmitted over a channel with 1 MHz bandwidth and a signal-to-noise ratio of 15. Using Shannon's capacity formula, what is the approximate maximum data rate?

  1. 16 Mbit/s
  2. 2 Mbit/s
  3. 4 Mbit/s Correct answer.
  4. 1 Mbit/s

Explanation

Shannon's law gives C = B log2(1 + S/N), so with B = 1 MHz and S/N = 15 the logarithm base 2 of 16 is 4. The capacity is therefore about 4 Mbit/s, the theoretical upper bound for error-free transmission.

Question 21Information, Electronics and Communications Technology (IECT)

A Zener diode with Vz = 6.2 V is used as a shunt regulator across a load, fed from a 12 V supply through a 470 ohm series resistor. Ignoring Zener current, what load current flows?

  1. About 38.7 mA
  2. About 12.3 mA Correct answer.
  3. About 6.2 mA
  4. About 25.5 mA

Explanation

The series resistor drops 12 − 6.2 = 5.8 V, so the current through it is 5.8/470 ≈ 12.3 mA. If the Zener current is neglected, essentially all of this current flows into the load, which sets the maximum usable load.

Question 22Information, Electronics and Communications Technology (IECT)

In a 4-bit two's complement system, what is the result of adding 0110 and 1011, and what does the sign of the result indicate?

  1. 0001 with no overflow Correct answer.
  2. 1111 with no overflow
  3. 10001 with overflow
  4. 0001 with overflow

Explanation

The sum 0110 + 1011 = 1 0001, and discarding the carry out of the sign bit leaves 0001. Since a positive and a negative number were added, overflow cannot occur, and the result +1 is correct.

Question 23Information, Electronics and Communications Technology (IECT)

An antenna with a gain of 20 dBi radiates 100 W. What is the effective isotropic radiated power?

  1. 10 000 W Correct answer.
  2. 1000 W
  3. 200 W
  4. 2000 W

Explanation

A gain of 20 dBi corresponds to a linear power ratio of 10^(20/10) = 100. Multiplying by the 100 W input gives an EIRP of 10 000 W, which quantifies the equivalent isotropic power in the peak direction.

Question 24Information, Electronics and Communications Technology (IECT)

A memory system uses 12 address lines and an 8-bit data bus. What is its total storage capacity in bytes?

  1. 8192 bytes
  2. 4096 bytes Correct answer.
  3. 2048 bytes
  4. 1024 bytes

Explanation

Twelve address lines select 2^12 = 4096 distinct locations, and each location holds one byte on the 8-bit bus. The total capacity is therefore 4096 bytes, or 4 KB.

Question 25Information, Electronics and Communications Technology (IECT)

A causal LTI system has the transfer function H(s) = 1/(s + 3). Which statement about its step response is correct?

  1. It oscillates indefinitely without decaying
  2. It remains zero for all time
  3. It grows linearly without bound
  4. It rises exponentially to a final value of 1/3 Correct answer.

Explanation

The pole at s = −3 lies in the left half-plane, so the system is stable and its step response is of the form (1/3)(1 − e^(−3t)). The output therefore settles at the DC gain of 1/3 with a time constant of one third of a second.

Question 26Information, Electronics and Communications Technology (IECT)

In a common-emitter BJT amplifier, which parameter is used to describe the small-signal current gain at a fixed collector-emitter voltage?

  1. h_oe
  2. h_fe or β_ac Correct answer.
  3. h_re
  4. h_ie

Explanation

The hybrid h-parameter h_fe (equivalently β_ac) is defined as the ratio of small-signal collector current change to base current change with the output port short-circuited for AC, i.e. at constant V_CE. The other h-parameters describe input impedance, reverse voltage feedback and output admittance respectively.

Question 27Information, Electronics and Communications Technology (IECT)

Which type of feedback is used in an oscillator circuit such as a Colpitts oscillator?

  1. Positive feedback with a total loop phase shift of 180 degrees
  2. Negative feedback with a phase shift of 180 degrees
  3. Positive feedback with a total loop phase shift of 360 degrees Correct answer.
  4. Negative feedback with a total loop phase shift of 0 degrees

Explanation

An oscillator requires regenerative (positive) feedback: the signal returning to the input must be in phase with the input, meaning the total loop phase shift around amplifier plus feedback network is 360 degrees (or 0 degrees). The Barkhausen criterion also requires loop gain of at least unity at the oscillation frequency.

Question 28Information, Electronics and Communications Technology (IECT)

In the 8085 microprocessor, which signal indicates that the CPU has placed a valid address on the address bus?

  1. ALE Correct answer.
  2. READY
  3. HOLD
  4. TRAP

Explanation

ALE (Address Latch Enable) goes high during T1 of each machine cycle to signal that the multiplexed AD0-AD7 lines carry the low-order address byte, which must be latched externally. This allows the address to be separated from the data that later appears on the same pins.

Question 29Information, Electronics and Communications Technology (IECT)

Which of the following is a characteristic of a star topology in a local area network?

  1. Nodes form a closed ring with token passing
  2. All nodes share a single coaxial cable backbone
  3. Every node connects to a central hub or switch Correct answer.
  4. Each node connects directly to every other node

Explanation

In a star topology each station has a dedicated point-to-point link to a central device such as a hub or switch. Failure of one link affects only that station, while failure of the central device disables the whole network.

Question 30Information, Electronics and Communications Technology (IECT)

Which IEEE 802.11 standard introduced operation in the 5 GHz band with orthogonal frequency-division multiplexing?

  1. 802.11b
  2. 802.11g
  3. 802.11a Correct answer.
  4. 802.11n

Explanation

IEEE 802.11a operates in the 5 GHz band and uses OFDM, giving data rates up to 54 Mbit/s. The 802.11b and 802.11g standards work in the 2.4 GHz band, with 802.11g also adopting OFDM.

Question 31Information, Electronics and Communications Technology (IECT)

Which property of an ideal operational amplifier implies that the voltage difference between its two input terminals is zero when negative feedback is applied?

  1. Infinite open-loop gain Correct answer.
  2. Zero output impedance
  3. Infinite bandwidth
  4. Infinite input impedance

Explanation

With infinite open-loop gain, any finite output requires an input differential of Vo/A, which tends to zero, giving the virtual-short condition. This is why the inverting input sits at the same potential as the non-inverting input in a feedback circuit.

Question 32Information, Electronics and Communications Technology (IECT)

Which number system uses the digits 0 to 9 and the letters A to F?

  1. BCD
  2. Binary
  3. Hexadecimal Correct answer.
  4. Octal

Explanation

Hexadecimal is base 16 and uses sixteen symbols: 0-9 followed by A-F representing decimal values 10-15. Each hex digit maps neatly to four binary bits, which is why it is common in microprocessor listings.

Question 33Information, Electronics and Communications Technology (IECT)

Which layer of the OSI reference model is responsible for end-to-end reliable delivery, including sequencing and retransmission?

  1. Network layer
  2. Transport layer Correct answer.
  3. Data link layer
  4. Session layer

Explanation

The transport layer (for example TCP) provides end-to-end connection-oriented service with sequence numbers, acknowledgements and retransmission of lost segments. The network layer handles logical addressing and routing between hosts.

Question 34Information, Electronics and Communications Technology (IECT)

A resistor of 2.2 kΩ has a tolerance of ±5 percent. What is the maximum resistance it may have?

  1. 2310 Ω Correct answer.
  2. 2420 Ω
  3. 2090 Ω
  4. 2200 Ω

Explanation

Five percent of 2200 Ω is 110 Ω, so the permitted range is 2090 Ω to 2310 Ω. The maximum value is therefore 2200 + 110 = 2310 Ω.

Question 35Information, Electronics and Communications Technology (IECT)

A coil has an inductance of 50 mH and a resistance of 10 Ω. What is its time constant?

  1. 5 ms Correct answer.
  2. 0.5 ms
  3. 500 ms
  4. 50 ms

Explanation

For an LR circuit the time constant is τ = L/R = 0.050 H / 10 Ω = 0.005 s, that is 5 ms. After one time constant the current reaches about 63 percent of its final value.

Question 36Information, Electronics and Communications Technology (IECT)

A parallel resonant LC circuit has L = 100 µH and C = 100 pF. What is its resonant frequency approximately?

  1. 1.59 MHz Correct answer.
  2. 15.9 MHz
  3. 159 kHz
  4. 3.18 MHz

Explanation

The resonant frequency is f = 1/(2π√(LC)). Here LC = 100e-6 × 100e-12 = 1e-14, so √(LC) = 1e-7 s and f = 1/(2π × 1e-7) ≈ 1.59 MHz.

Question 37Information, Electronics and Communications Technology (IECT)

A 1 kΩ resistor carries a current of 20 mA. What power is dissipated in it?

  1. 20 W
  2. 0.4 W Correct answer.
  3. 0.02 W
  4. 2 W

Explanation

Power in a resistor is P = I²R = (0.02 A)² × 1000 Ω = 0.0004 × 1000 = 0.4 W. Equivalently, the voltage is 20 V and P = VI = 20 × 0.02 = 0.4 W.

Question 38Information, Electronics and Communications Technology (IECT)

In an 8-bit DAC, the full-scale output is 10.2 V. What is the output for a digital input of 10000000?

  1. 1.275 V
  2. 10.2 V
  3. 5.1 V Correct answer.
  4. 2.55 V

Explanation

The input 10000000 equals decimal 128, which is half of the 256 possible codes. The output is therefore half of full scale, 10.2 × 128/256 = 5.1 V. This is the mid-scale step of the converter.

Question 39Information, Electronics and Communications Technology (IECT)

A 741 operational amplifier is connected as a voltage follower. What is the approximate closed-loop voltage gain?

  1. Infinite
  2. Unity Correct answer.
  3. Zero
  4. Equal to the open-loop gain

Explanation

In a voltage follower the output is fed back directly to the inverting input, so the feedback fraction is one and the closed-loop gain is 1/(1+A) × A ≈ 1. The circuit provides high input impedance and low output impedance with no voltage amplification.

Question 40Information, Electronics and Communications Technology (IECT)

A 555 timer is configured as an astable multivibrator with R1 = 10 kΩ, R2 = 10 kΩ and C = 0.1 µF. Which expression gives the output frequency?

  1. 1 / (2π√(R1R2C))
  2. 1.44 / ((2R1 + R2)C)
  3. 0.693 / ((R1 + R2)C)
  4. 1.44 / ((R1 + 2R2)C) Correct answer.

Explanation

For the standard astable 555 circuit, the capacitor charges through R1 + R2 and discharges through R2 only, giving t_high = 0.693(R1+R2)C and t_low = 0.693R2C. The period is therefore 0.693(R1+2R2)C and the frequency is 1.44/((R1+2R2)C).

Question 41Information, Electronics and Communications Technology (IECT)

In a 7-bit ASCII code, an odd parity bit is appended. What is the transmitted 8-bit word for the character whose 7-bit code is 1000001?

  1. 10000011
  2. 10000010
  3. 11000001 Correct answer.
  4. 01000001

Explanation

The 7-bit code 1000001 contains two 1s, which is even. For odd parity the added bit must make the total number of 1s odd, so the parity bit is 1 and it is placed in the most significant position, giving 11000001.

Question 42Information, Electronics and Communications Technology (IECT)

In a 4-variable Karnaugh map, a group of four adjacent cells that forms a 2×2 block corresponds to which simplification?

  1. Elimination of two variables from the term Correct answer.
  2. Elimination of one variable from the term
  3. No simplification at all
  4. Elimination of three variables from the term

Explanation

A group of 2^n adjacent cells eliminates n variables, because those variables take both values within the group. A 2×2 block contains four cells, so n = 2 and two variables drop out, leaving a two-literal product term.

Question 43Information, Electronics and Communications Technology (IECT)

A 3-input AND gate has inputs A, B and C. If A = 1, B = 1 and C = 0, and then C changes to 1 while A and B remain unchanged, what is the change in the output?

  1. The output changes from 1 to 0
  2. The output remains 0 throughout
  3. The output remains 1 throughout
  4. The output changes from 0 to 1 Correct answer.

Explanation

An AND gate outputs 1 only when all inputs are 1. With C = 0 the output is 0; when C becomes 1 all three inputs are 1 and the output becomes 1.

Question 44Information, Electronics and Communications Technology (IECT)

A 4-bit binary counter is clocked continuously from 0000. After 13 clock pulses, what is its binary state?

  1. 1101 Correct answer.
  2. 1110
  3. 1011
  4. 1100

Explanation

A 4-bit counter counts modulo 16, so after 13 pulses the state equals the binary representation of decimal 13. Decimal 13 is 8 + 4 + 1, which gives 1101.

Question 45Information, Electronics and Communications Technology (IECT)

A 16-bit address bus and an 8-bit data bus are used in a memory system. What is the maximum addressable memory in kilobytes?

  1. 32 KB
  2. 128 KB
  3. 64 KB Correct answer.
  4. 16 KB

Explanation

Sixteen address lines give 2^16 = 65 536 distinct addresses. With one byte per address this is 65 536 bytes, which equals 64 KB.

Question 46Information, Electronics and Communications Technology (IECT)

Which statement correctly distinguishes a microprocessor from a microcontroller?

  1. A microprocessor always contains on-chip flash memory, while a microcontroller does not
  2. A microprocessor is designed only for embedded control, while a microcontroller is for general computing
  3. A microcontroller is always faster in clock speed than a microprocessor
  4. A microcontroller integrates CPU, memory and peripherals on one chip, while a microprocessor provides mainly the CPU Correct answer.

Explanation

A microcontroller is a complete computer on a chip, combining the processor core with RAM, program memory, timers and I/O peripherals for embedded control. A microprocessor is primarily the CPU and relies on external memory and interface chips.

Question 47Information, Electronics and Communications Technology (IECT)

A transmission line has a characteristic impedance of 50 Ω and is terminated by a purely resistive load of 50 Ω. What is the reflection coefficient at the load?

  1. One
  2. Minus one
  3. Zero Correct answer.
  4. 0.5

Explanation

The reflection coefficient is Γ = (Z_L − Z_0)/(Z_L + Z_0). With Z_L = Z_0 = 50 Ω the numerator is zero, so Γ = 0 and all incident power is absorbed by the load with no reflected wave.

Question 48Information, Electronics and Communications Technology (IECT)

In a PCM system, a signal is quantised into 256 levels and sampled at 8 kHz. What is the resulting bit rate?

  1. 64 kbit/s Correct answer.
  2. 8 kbit/s
  3. 128 kbit/s
  4. 256 kbit/s

Explanation

With 256 levels each sample needs log2(256) = 8 bits. At 8000 samples per second the bit rate is 8000 × 8 = 64 000 bit/s, the standard DS0 rate.

Question 49Information, Electronics and Communications Technology (IECT)

A superheterodyne receiver has an RF signal at 1000 kHz and a local oscillator at 1455 kHz. What is the intermediate frequency, and what is the image frequency?

  1. 455 kHz and 1455 kHz
  2. 1000 kHz and 1910 kHz
  3. 455 kHz and 1910 kHz Correct answer.
  4. 455 kHz and 1000 kHz

Explanation

The intermediate frequency is the difference between the local oscillator and the signal: 1455 − 1000 = 455 kHz. The image frequency lies symmetrically on the other side of the oscillator, at 1455 + 455 = 1910 kHz.

Question 50Information, Electronics and Communications Technology (IECT)

A 4-bit flash ADC is required to convert an analogue input with a full-scale range of 4 V. How many comparators are needed, and what is the resolution?

  1. 15 comparators and 0.267 V
  2. 8 comparators and 0.5 V
  3. 16 comparators and 0.25 V
  4. 15 comparators and 0.25 V Correct answer.

Explanation

An n-bit flash converter uses 2^n − 1 comparators, so a 4-bit design needs 15. The resolution is full scale divided by 2^n, giving 4 V / 16 = 0.25 V per code.