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Past Questions
The binary number 10101 in decimal is—
A)
20
B)
21
C)
30
D)
31
To convert a binary number to a decimal number, we multiply each bit by 2 raised to the power of its position (starting from 0 on the rightmost side) and sum the results.
Given binary number: 10101
Calculation:
- The bit at position 0 (rightmost) is 1: 1 × 2^0 = 1 × 1 = 1
- The bit at position 1 is 0: 0 × 2^1 = 0 × 2 = 0
- The bit at position 2 is 1: 1 × 2^2 = 1 × 4 = 4
- The bit at position 3 is 0: 0 × 2^3 = 0 × 8 = 0
- The bit at position 4 (leftmost) is 1: 1 × 2^4 = 1 × 16 = 16
Sum = 16 + 0 + 4 + 0 + 1 = 21
Therefore, the binary number 10101 is equal to 21 in decimal.
Comparing with options:
- a. 20: Incorrect (This would be 10100 in binary)
- b. 21: Correct
- c. 30: Incorrect (This would be 11110 in binary)
- d. 31: Incorrect (This would be 11111 in binary)
What type of integration is chosen to fabricate Integrated Circuits like Counters, multiplexers and Adders?
A)
Small Scale Integration (SSI)
B)
Medium Scale Integration (MSI)
C)
Large Scale Integration (LSI)
D)
Very Large Scale Integration (VLSI)
Integrated Circuits (ICs) are classified based on the number of logic gates or transistors integrated onto a single chip.
1. Small Scale Integration (SSI): Typically contains fewer than 10 gates. Examples include basic logic gates (AND, OR, NOT) and flip-flops.
2. Medium Scale Integration (MSI): Typically contains between 10 and 100 gates. This level of integration is specifically used to create functional blocks such as Counters, Multiplexers, Decoders, and Adders.
3. Large Scale Integration (LSI): Contains 100 to 10,000 gates. Examples include early 8-bit microprocessors and small memory chips.
4. Very Large Scale Integration (VLSI): Contains 10,000 to millions of gates. Examples include modern microprocessors, GPUs, and complex System-on-Chips (SoCs).
Since Counters, Multiplexers, and Adders are complex functional blocks but do not reach the scale of a full processor or large memory array, they fall under the Medium Scale Integration (MSI) category.
Which among the single operand instructions complement the accumulator without affecting any of the flags?
A)
CLR
B)
SETB
C)
CPL
D)
APC
The question refers to the 8051 microcontroller instruction set.
1. **CPL A (Complement Accumulator)**: This is a single-operand instruction that performs a logical NOT operation on every bit of the accumulator. Crucially, the 8051 architecture specifies that the CPL A instruction does not affect any of the flags in the Program Status Word (PSW), such as the Carry (C), Auxiliary Carry (AC), or Overflow (OV) flags.
2. **CLR (Clear)**: While CLR can be used as a single operand (e.g., CLR A), it sets all bits to 0 rather than complementing them.
3. **SETB (Set Bit)**: This is a bit-oriented instruction used to set a specific bit to 1. It is not used to complement the entire accumulator.
4. **APC**: This is not a standard 8051 instruction. (The user might be thinking of ADC - Add with Carry, which is a two-operand instruction and heavily affects flags).
Therefore, CPL is the only instruction that complements the accumulator without altering the flags.
The flash type A/D converters are called as —
A)
Parallel non-inverting A/D converter
B)
Parallel counter A/D converter
C)
Parallel inverting A/D converter
D)
Parallel comparator A/D converter
A Flash Analog-to-Digital Converter (ADC) is the fastest type of ADC. It operates by using a series of comparators that work in parallel to compare the input analog voltage against a set of reference voltages generated by a resistor ladder.
1. **Working Principle**: For an n-bit converter, it requires (2^n - 1) comparators. Each comparator compares the input signal to a specific reference level.
2. **Parallel Operation**: Because all comparators operate simultaneously (in parallel), the conversion happens almost instantaneously, which is why it is called a 'Flash' converter.
3. **Output**: The outputs of these comparators form a 'thermometer code,' which is then converted into a binary code using a priority encoder.
Why other options are incorrect:
- **Option a & c**: 'Inverting' or 'Non-inverting' refers to operational amplifier configurations, not the fundamental architecture of a Flash ADC.
- **Option b**: 'Counter' refers to a different type of ADC (Counter-type or Successive Approximation), which operates sequentially rather than in parallel, making it significantly slower than a Flash ADC.
FET are classified into two type they are —
A)
3 terminal FET and 2 terminal FET
B)
Drain less and Source less
C)
Power FET and Non Power FET
D)
Majority carrier and minority carrier
Field Effect Transistors (FETs) are fundamentally 'unipolar' devices. This means that the current flow is carried by only one type of charge carrier—either electrons (in n-channel FETs) or holes (in p-channel FETs). Because the current is conducted by the majority carriers of the semiconductor material, FETs are classified based on this characteristic. In contrast, Bipolar Junction Transistors (BJTs) are 'bipolar' because they involve both majority and minority carriers.
Analyzing the options:
- Option (a) is incorrect because all standard FETs (JFET and MOSFET) are 3-terminal devices (Gate, Drain, Source).
- Option (b) is incorrect as Drain and Source are essential terminals for the device to function.
- Option (c) is a categorization based on application/power rating, not a fundamental classification of the device type.
- Option (d) is the correct technical classification regarding the nature of charge carriers in the device.
The picture is the symbol for—
A)
LED
B)
Zener diode
C)
Photo diode
D)
Dual diode
The symbol described (triangle with bar and bent ends) is typical for Zener diode; LED has arrows outward.
Which circuit is used to generate a sawtooth wave?
A)
Integrator
B)
Differentiator
C)
Ramp generator
D)
Astable multivibrator
A sawtooth wave is a waveform that rises linearly (a ramp) and then drops sharply back to its starting point.
1. **Ramp Generator (Correct):** A ramp generator is specifically designed to produce a voltage that increases linearly with time. When this linear ramp is combined with a rapid discharge or reset mechanism, it creates a sawtooth waveform. Therefore, it is the primary circuit used for this purpose.
2. **Integrator (Incorrect):** While an integrator can produce a ramp voltage if the input is a constant DC voltage, an 'integrator' is a general-purpose circuit. A 'Ramp Generator' is the specific application/circuit name for generating this waveform.
3. **Differentiator (Incorrect):** A differentiator produces a spike or a pulse when the input changes linearly. It is used to detect edges or rates of change, not to generate a continuous sawtooth wave.
4. **Astable Multivibrator (Incorrect):** An astable multivibrator is a free-running oscillator that typically generates a square wave or a rectangular wave, not a linear ramp/sawtooth wave.
How are the status of the carry, auxiliary carry and parity flag affected if the write instruction MOV A,#9CH ADD A,#64H
A)
CY=0,AC=0,P=0
B)
CY=1,AC=1,P=0
C)
CY=0,AC=1,P=0
D)
CY=1,AC=1,P=1
Step-by-step calculation for the 8051 microcontroller instruction sequence:
1. **Initial Values**:
- MOV A, #9CH: Accumulator (A) = 9CH (Binary: 1001 1100)
- ADD A, #64H: Add 64H (Binary: 0110 0100) to A.
2. **Binary Addition**:
```
1001 1100 (9CH)
+ 0110 0100 (64H)
------------
1 1111 1100 (Result: FCH, with a carry out)
```
3. **Evaluating Flags**:
- **Carry Flag (CY)**: The addition results in a carry out from the Most Significant Bit (MSB). Therefore, **CY = 1**.
- **Auxiliary Carry (AC)**: The AC flag is set if there is a carry from bit 3 to bit 4.
Looking at the lower nibbles: 1100 (C) + 0100 (4).
Binary: 1100 + 0100 = 1 0000.
Since there is a carry from the 3rd bit position to the 4th, **AC = 1**.
- **Parity Flag (P)**: The parity flag in the 8051 reflects the number of 1s in the Accumulator.
The result in A is FCH (Binary: 1111 1100).
Counting the 1s: there are six 1s.
Since 6 is an even number, the Parity flag (which is 1 for odd parity and 0 for even parity in 8051) is **P = 0**.
4. **Conclusion**:
CY = 1, AC = 1, P = 0. This matches option (b).
What will be the backup time of a UPS if it is backed by a 150 Ah, 12V battery driving a load of 150W?
A)
14 hour
B)
10 hour
C)
12 hour
D)
16 hour
To calculate the backup time of a UPS, we first determine the total energy stored in the battery and then divide it by the power consumption of the load.
1. **Calculate Total Energy (Wh):**
Energy (Watt-hours) = Battery Capacity (Ah) × Battery Voltage (V)
Energy = 150 Ah × 12 V = 1800 Wh
2. **Calculate Backup Time (t):**
Backup Time = Total Energy (Wh) / Load Power (W)
Backup Time = 1800 Wh / 150 W = 12 hours
Therefore, the battery can support a 150W load for 12 hours.
Note: In real-world scenarios, efficiency losses of the inverter (typically 10-20%) and battery discharge depth limits would reduce this time, but in standard competitive exam problems of this type, ideal calculations are expected unless an efficiency percentage is provided.
The cycle required to fetch and execute an instruction in a 8085 microprocessor is which one of the following?
A)
Clock cycle
B)
Memory cycle
C)
Machine cycle
D)
Instruction cycle
In the 8085 microprocessor, the timing and execution of instructions are categorized into a hierarchy of cycles:
1. **Instruction Cycle**: This is the total time required to fetch and execute one complete instruction. It consists of one or more machine cycles. For example, a simple instruction like 'MOV A, B' takes one machine cycle, while 'LDA 2000H' takes multiple machine cycles (Opcode fetch, Memory read, Memory read).
2. **Machine Cycle**: This is the time required to complete one operation of accessing memory or an I/O device (e.g., Opcode Fetch cycle, Memory Read cycle, Memory Write cycle). An instruction cycle is composed of one or more machine cycles.
3. **T-State (Clock Cycle)**: This is the smallest unit of time, corresponding to one period of the system clock. A machine cycle consists of several T-states (usually 3 to 6).
4. **Memory Cycle**: This is a specific type of machine cycle used to access memory.
Since the question asks for the cycle required to both 'fetch and execute' an instruction, the correct term is the Instruction Cycle.
Logic table below gives the output for input A and B. The logic operation performed is —
A)
Negative NOR
B)
Ex.OR
C)
NAN
D)
Negative of Ex. OR
Table with 0,0->0, 0,1->1, 1,0->1, 1,1->0 corresponds to Ex-OR operation.
A certain D-MOSFET is biased at VGS = 0V. Its data sheet specifies IDSS = 20mA and VGS(off) = -5V. The value of the drain current is —
A)
20mA
B)
0mA
C)
40mA
D)
10mA
1. Understanding the Device: A Depletion-mode MOSFET (D-MOSFET) is a device that can conduct current even when the gate-to-source voltage (VGS) is zero.
2. Definition of IDSS: The term IDSS stands for 'Drain-to-Source saturation current with VGS = 0V'. By definition, IDSS is the current that flows from the drain to the source when the device is in the saturation region and the gate is shorted to the source (VGS = 0V).
3. Given Data:
- VGS = 0V
- IDSS = 20mA
- VGS(off) = -5V
4. Calculation: Since the question explicitly states that the MOSFET is biased at VGS = 0V, the drain current (ID) is equal to the IDSS value provided in the data sheet.
ID = IDSS = 20mA.
5. Analysis of Options:
- Option (a) 20mA: Correct, as it matches the definition of IDSS at VGS = 0V.
- Option (b) 0mA: Incorrect; this would occur if VGS was equal to or less than VGS(off) (-5V).
- Option (c) 40mA: Incorrect; this would require a positive VGS (enhancement mode operation).
- Option (d) 10mA: Incorrect; this would occur at a specific negative VGS between 0V and -5V.
How many SFR (Special Function Register) are there in 8051 microcontroller?
A)
21
B)
12
C)
16
D)
8
In the standard Intel 8051 microcontroller architecture, the Special Function Registers (SFRs) are used to control and monitor the operation of the microcontroller. These registers are mapped to the upper 128 bytes of the internal RAM (addresses 80H to FFH). There are exactly 21 SFRs in the standard 8051. These include:
1. Accumulator (ACC)
2. B Register
3. PSW (Program Status Word)
4. SP (Stack Pointer)
5. TMOD (Timer Mode)
6. TCNT0 (Timer 0 Counter)
7. TCNT1 (Timer 1 Counter)
8. TCON (Timer Control)
9. SCON (Serial Control)
10. SBUF (Serial Buffer)
11. IE (Interrupt Enable)
12. IP (Interrupt Priority)
13. P0 (Port 0)
14. P1 (Port 1)
15. P2 (Port 2)
16. P3 (Port 3)
17. DPTRH (Data Pointer High)
18. DPTRL (Data Pointer Low)
19. DIV (Divide - in some variants)
20. T2CON (Timer 2 Control - in 8052)
21. T2 (Timer 2 - in 8052)
While the basic 8051 has a core set, the standard technical answer for competitive exams regarding the 8051 family (often including the 8052 enhancements) is 21. Options b, c, and d are numerically incorrect based on the architectural specifications of the 8051.
If the frequency of 50Hz is supply to full wave rectifier, What will be the output frequency?
A)
25Hz
B)
50Hz
C)
75Hz
D)
100Hz
In a full-wave rectifier, both the positive and negative half-cycles of the input AC sine wave are converted into positive DC pulses.
1. Input Frequency (f_in): The supply frequency is given as 50 Hz. This means there are 50 complete cycles (one positive and one negative peak) per second.
2. Rectification Process: A full-wave rectifier (whether center-tapped or bridge) flips the negative half-cycle to positive. Consequently, for every one cycle of the input AC, the output produces two pulses of DC.
3. Output Frequency Calculation: The ripple frequency (f_out) of a full-wave rectifier is twice the input frequency.
Formula: f_out = 2 * f_in
Calculation: f_out = 2 * 50 Hz = 100 Hz.
Therefore, the output frequency is 100 Hz.
- Option (a) 25Hz is incorrect as it suggests a frequency reduction.
- Option (b) 50Hz is the frequency of a half-wave rectifier.
- Option (c) 75Hz has no theoretical basis in standard rectification.
The central portion of a propeller shaft is made from a
A)
Steel shaft
B)
Gun metal shaft
C)
Steel tube
D)
Cast iron rod
Based on established principles in the relevant subject area, the correct and most appropriate choice is 'Cast iron rod' (Option D).
Which letter is on the opposite face of X? (Given faces: Z U W, Y V X, W Z V)
A)
Z
B)
W
C)
Y
D)
U
Based on established principles in Reasoning & Mental Ability, the correct and most appropriate choice is 'W' (Option B).
Low boiling point refrigerant are preferably suited for
A)
Reciprocating compressors.
B)
Large centrifugal pump
C)
Large axial flow rotary pump
D)
All of these
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'All of these' (Option D).
When actual discharge of a reciprocating pump is more than theoretical discharge, the difference between theoretical discharge and actual discharge is known as
A)
Slip of the pump
B)
Slip of the piston
C)
Slip of the cylinder
D)
Slip of the fluid
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'Slip of the fluid' (Option D).
The purpose of gear in an automobile is to
A)
Vary Speed
B)
Vary torque
C)
Provide constant speed
D)
Disconnect the road wheels from the engine when desired
Based on established principles in the relevant subject area, the correct and most appropriate choice is 'Provide constant speed' (Option C).
The three types of cost estimation are- (i) Order of magnitude estimate (ii) Budget estimate and
A)
Forecasting estimate
B)
Definitive estimate
C)
Product estimate
D)
Both (a) & (b)
Based on established principles in Indian Economy, the correct and most appropriate choice is 'Forecasting estimate' (Option A).
The purpose of tyre rotation on automobiles is to
A)
Avoid ply separation
B)
Equalize wear
C)
Get better ride
D)
None of these
Tyre rotation means periodically changing the position of tyres on the vehicle so that all tyres wear more uniformly. Since front and rear tyres often experience different loads, steering, and braking forces, rotation helps equalize wear and extend tyre life. Option (a) is incorrect because ply separation is a tyre defect, not the purpose of rotation. Option (c) is incorrect because tyre rotation is not primarily done to improve ride quality, though uniform wear may indirectly help. Option (d) is incorrect because option (b) is the correct purpose.
An engine in which the combustion process starts when the air-fuel mixture self-ignites due to high temperature in the combustion chamber caused by high compression is called
A)
Spark ignition
B)
Compression ignition
C)
Direct injection
D)
Displacement
The correct answer is **compression ignition**. In this type of engine, air is compressed to a very high pressure and temperature, and when fuel is injected into the hot compressed air, it self-ignites without the need for a spark. This is the principle used in diesel engines.
- **Spark ignition (a)** is incorrect because it uses a spark plug to ignite the air-fuel mixture, as in petrol engines.
- **Direct injection (c)** is incorrect because it refers to a fuel injection method, not the ignition principle itself.
- **Displacement (d)** is incorrect because it is a measure of engine volume, not a type of ignition or combustion process.
It is necessary that before the pump is started, its casing together with impeller and the Suction pipe must be filled with water in order to remove the air, gas or vapour in that region. This process is called
A)
Sucking
B)
Priming
C)
Drawing
D)
Pumping
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'Drawing' (Option C).
Water hammer is a phenomenon which is caused by
A)
Sudden opening of a valve in a pipeline
B)
Sudden closure (partial or complete) of a valve in a pipeline
C)
Incompressibility of fluid
D)
The pipeline material being elastic
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'The pipeline material being elastic' (Option D).
In vapour compression refrigeration system the heat is absorbed from the environments to be cooled by
A)
Evaporator
B)
Condenser
C)
Compressor
D)
Throttle valve
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'Condenser' (Option B).