PRE-BOARD EXAMINATION

the capacitors and Vcc appear as ac shorts

In the ac equivalent circuit of a transistor amplifier,

emitter is positive with respect to base and base is positive with respect to collector

In a p-n-p transistor operating in forward active mode:

8 thyristors and 8 diodes

Modified Mc Murray full bridge inverter uses:

Primary memory

During processing the instructions, data, intermediate results and final results in a computer are held in:

has the same potential as ground, yet it can sink no current.

In an inverting amplifier, a virtual ground:

decreases

A sinusoidal voltage is applied across an inductor. when the frequency of the voltage is increased, the current ____.

The source follower.

Which of the following JFET amplifiers has a high Z_in, a low Z_out, and a voltage gain less than one?

low-pass

In an ac circuit, an output capacitor and a resistor are connected in series with an ac signal. What filter action will be the result?

can be used to build all the other types of gates

The NAND or NOR gates are referred to as "universal" gates because either:

zero or negative

If the absolute value of a number is less than decimal 1, the sign of exponent in floating point representation is:

0.1

If the minority carrier lifetime and diffusion constant in a semiconductor material are respectively 100 μs and 100 cm²/sec, then what is the diffusion length in cm?

200 μA

In CE connection, the leakage current of a transistor is about:

are never on together

A TTL totem-pole circuit is designed so that the output transistors:

as a combination of series and parallel

When placed into a circuit, how are electronic components usually connected?

class C

Which of the following classes of amplifier operation has the highest power efficiency?

α to π + α and π + π to 2π + α

From the circuit shown below, the load is highly inductive. The firing angle is α for each of the thyristors. What are the periods of conduction for Th₁ and Th₂ respectively?

a LOW on all gate enable inputs

What control signals may be necessary to operate a 1-line-to-16 line decoder?

Both A and R are true and R is correct explanation of A

ssertion (A): The hybrid p model of a transistor can be reduced to h parameter model and vice versa.Reason (R): Hybrid π and h parameter models are interrelated as both of them describe the same device.

maximum rate at which its output voltage can change

The slew-rate specification of an op amp is the:

Rectangular

A fully controlled bridge converter feeds a highly inductive load such that the load current can be assumed to be constant. What is the wave shape of input current?

source current

The output current capability of a single 7400 NAND gate when HIGH is called _____.

Q1-OFF, Q2-ON, Q3-OFF, Q4-ON

Q1-OFF, Q2-ON,

Using the schematic diagram of a TTL NAND gate, determine the state of each transistor (ON or OFF) when all inputs are high.

Pin 6 should be pulsing.

A logic probe is used to test the pins of a 7411 IC with the following results. Is there a problem with the chip and if so, what is the problem?

42.53, 0.85 μA

Determine the stability factor and change in Ic from 25°C to 100°C for, β = 50, R_B/ R_E = 250, △I_C0 = 19.9 nA for emitter bias configuration.

I, III and IV only

Consider the following statements with respect to the feedback of the control systems.

I. Feedback can improve stability or be harmful to stability if it is not properly applied.

II. Feedback can always improve stability

III. In many situations the feedback can reduce the effect of noise and disturbance on system performance.

IV. In general the sensitivity of the system gain of a feedback system of a parameter variation depends on where the parameter is located.

Oscillator

Which of the following elements is not used in an automatic control system?

plate separation

The strength of an electric field at a given point is proportional to the potential difference on the plates and inversely proportional to the:

1+βA

What is the ratio of the input impedance with series feedback to that without feedback?

Both A and R are correct but R is not correct explanation of A

Assertion (A): In register indirect addressing mode of 8085, the address of operand is in the specified register.Reason (R): An example of register indirect addressing mode is MOV, A, M.

440 V

A star-connected load consists of three identical coils each of resistance 30 Ω and inductance 127.3 mH. If the line current is 5.08 A, calculate the line voltage if the supply frequency is 50 Hz.

-3.85

Determine the voltage gain with feedback for voltage-series feedback having A = -100, R₁ = 15 kΩ, Ro = 20 kΩ, and a feedback of β = -0.25.

Both 20 dB/decade and 6 dB/octave

For a first-order, active low-pass filter how fast does the output voltage roll off above the cutoff frequency?

leads the voltage by π/2 rad

When a capacitor is connected to an a.c. supply the current:

only inside the shell

The electric field due to a uniform distribution of charge on a spherical shell is zero:

IC = FC + EC

IC (instruction cycle), FC (fetch cycle) and EC (executive cycle) are related as:

solve for the total current and resistance

The first goal to accomplish in analyzing a complex series-parallel circuit is to:

volume control

One of the most common applications of a potentiometer is as an adjustable voltage divider, also known as

1 + 1 + 0 + 0 = 1

Which of the following equations would accurately describe a four-input OR gate when A = 1, B = 1, C = 0, and D = 0?

Fermi-Dirac Distribution

What do you call the probability giving distribution of electrons over a range of allowed energy levels?

MEM MAKER

Which DOS command improves memory usage?

Concentrated refresh

'Burst refresh' in DRAM is also called

sum of the total currents flowing out of a junction equals the sum of the total currents flowing into that junction

Kirchhoff's current law for parallel circuits states that the:

From the following specifications determine the fan-out for the logic family.

HIGH state is 8, LOW state is 16

A JFET operates in ohmic region when:

V_GS is less than pinch off voltage

leads the source voltage

In a series RLC circuit that is operating below the resonant frequency, the current

Both A and R are true and R is correct explanation of A

Assertion (A) : A p-n junction has high resistance in reverse direction.Reason (R) : When a reverse bias is applied to p-n junction, the width of depletion layer increases.

31 V

If a periodic voltage has following value for equal time intervals changing suddenly from one value to next... 0, 5, 10, 20, 50, 60, 50, 20, 10, 5, 0, -5, -10 etc., then what is the rms value of the waveform?

54XX has a wider power supply and expanded temperature range.

What is the difference between the 54XX and 74XX series of TTL logic gates?

Stochastic control system

A control system working under unknown random actions is called ____________

i = i + 1

Expression ++i is equivalent to

Insensitive to the parameter variation but sensitive to the input commands

What is the characteristic of a good control system?

increased

To reduce the current in a series RL circuit, the frequency should be:

27.27 μA

A difference amplifier has two inputs V₁ = 5V and V₂ = 3V. If R₁ = 10 kilo-ohms and R₂ = 100 kilo-ohms, find the current exiting the positive terminal of source V₂.

Field controlled D.C. motor

Which of the following is an open loop control system?

in the same direction as the field

For loop of a current-carrying wire in a uniform magnetic field the potential energy is a minimum if the magnetic dipole moment of the loop is:

R_B1/(R_B1+R_B2)

For a UJT, the intrinsic standoff ratio, η, equals

cannot be determined without values

If the frequency is doubled and the resistance is halved, the impedance of a series RL circuit

5RC

An uncharged capacitor and a resistor are connected in series with a switch and a 12 V battery. The capacitor will reach full charge in a time equal to approximately:

the force acting on a test charge

An electric field is most directly related to:

Magnetic tape

Which of the following can be accessed only sequentially?

Both A and R are correct and R is correct explanation of A

Assertion (A): Dynamic RAM needs refreshing.Reason (R): Capacitors tend to lose charge.

slow down

An electron traveling north enters a region where the electric field is uniform and points north. The electron:

Low and lagging

Generally, what is the power factor at the input terminals of a cyclo- converter?

if the particle is moving across the field lines

A magnetic field exerts a force on a charged particle:

exclusive-OR

What logic function is the sum output of a half-adder?

1.67

The capacitance of a parallel plate capacitor is 1000 pF. It has 19 plates, each 50 mm by 30 mm separated by a dielectric of thickness 0.40 mm. Determine the relative permittivity of the dielectric.

Both A and R correct but R is not correct explanation of A

Assertion (A): Thyristors can be used in controlled heating, excitation systems of alternators, speed control of motors and HVDCReason (R): A static var system using thyristors is very commonly used in high voltage ac systems.

I_Ep >> I_En

If in a p-n-p transistor the current IE has two components viz. I_Ep due to injection of holes from p-region to n-region and I_E due to injection of electrons from n-region to p-region, then:

half cycle of the input signal

In a full wave rectifier, the current in each of the diodes flows for:

Decreases

With negative feedback in a closed loop control system, the system sensitivity to parameter variation:

AND gate

Output will be a LOW for any case when one or more inputs are zero for a(n):

A = 0, B = 0, C = 0

From the truth table for a three-input NOR gate, what is the only condition of inputs A, B, and C that will make the output X high?

69 Ω

A coil of aluminum wire has a resistance of 50 Ω when its temperature is 0°C. Determine its resistance at 100°C if the temperature coefficient of resistance of aluminum at 0°C is 0.0038/°C

Superposition

The primary of the method of analyzing a circuit with two or more voltage sources is usually

the ac load line is steeper than the dc load line.

In an RC-coupled class A amplifier,

In phase with the current

In a series RC circuit, the voltage across the resistance is:

3, 2, 3

The total number of leads in SCR, DIAC and TRIAC respectively are:

a voltage source in series with a resistance

A Thevenin equivalent circuit consist of:

0.034 Ω-m

Calculate the resistivity of n-type semiconductor from the following data: Density of holes = 5 x 10¹²cmˉ³, Density of electrons = 8 x 10¹³ cmˉ³, Mobility of conduction electron = 2.3 x 10⁴ cm²/ V-sec and Mobility of holes = 100 cm²/V-sec.

Av decreases.

In a common-emitter amplifier, what happens to the voltage gain, Av, when a load resistor, R_L, is connected to the output?

zero.

The dc emitter current in each transistor of a differential amplifier equals:

a few kilobytes

The size of cache memory in most microcomputers is about:

1/R

The magnetic field outside a long straight current-carrying wire depends on the distance R from the wire axis according to:

field lines are close together where the field is large

Choose the correct statement concerning electric field lines:

Increases

When the frequency of an a.c. circuit containing resistance and capacitance is increased the impedance:

Apparent over True power gives power factor

Which of the following statements is false?

holes and electrons

At room temperature the current in an intrinsic semiconductor is due to:

Decreases

When an additional resistor is connected across existing parallel circuit, the total resistance

3558.81 Hz

Calculate the resonant frequency of this Wien bridge oscillator if R₁ = 25 kΩ, R₂ = 40 kΩ, C₁ = 0.001 μF, and C₂ = 0.002 μF.

5 Ω

Some wire of cross-sectional area 1 mm² has a resistance of 20 Ω. Determine the resistance of a wire of the same length and material if the cross-sectional area is 4 mm².

V_L > V_R

An inductor and a resistor are in series with a sinusoidal voltage source. The frequency is set so that the inductive reactance is equal to the resistance. If the frequency is increased, then