Ques 2. For highest power gain, what configuration is used

CC

CE✓

CB

CS

Out of the three transistor connections, the common emitter circuit is the most efficient. It is used in about 90 to 95 percent of all transistor applications. The main reasons for this are :

The transistor circuit will have a moderately high input impedance

Low output impedance

Moderately high current gain

Moderately high voltage gain and very good and wide range of frequency response and hence find dominant applications in voltage, current and power amplifiers.

High current gain

In common emitter connection, I_{c} is the output current and I_{B} is the input current. The collector current here is expressed as:

Ic = βI_{B} + I_{CEO} Where β = Current Gain I_{CEO} = Collector-Emitter current

As the value of β is very large, therefore, the output current I_{C} is much more than the input current I_{B}. This increases the current gain effectively. The current gain of CE arrangement ranges from 20 to 500.

High Voltage and Power Gain

As we have seen above, CE arrangement has the high current gain. This is turn, increases the voltage and power gain of CE circuit. In comparison to CB and CC circuits, the common emitter connection has the highest voltage and power gain. For this reason, the CE transistor connection is often used for amplifying purposes.

Ques 3. An SCR has …… PN junctions

Two

Four

Three✓

One

A silicon controlled rectifier or semiconductor-controlled rectifier is a four-layer solid-state current-controlling unidirectional devices (i.e. can conduct current only in one direction).

The silicon control rectifier (SCR) consists of four layers of semiconductors, which form NPNP or PNPN structures, having three P-N junctions labeled J_{1}, J_{2} and J_{3}, and three terminals. Silicon is used as the intrinsic semiconductor, to which the proper dopants are added. The junctions are either diffused or alloyed (an alloy is a mixed semiconductor or a mixed metal). The anode terminal of an SCR is connected to the p-type material of a PNPN structure, and the cathode terminal is connected to the n-type layer. SCR is connected to the p-type material nearest to the cathode.

Ques 4. A pole pitch in an electrical machine is

Equal to 180° Electrical✓

Equal to 180° Mechanical

Less than 180° electrical

Greater than 180° electrical

Pole pitch may be defined as the distance between the two adjacent poles, which is nothing but the periphery of the armature divided by the number of poles. In other words, it is the number of armature conductors or number of armature slots per pole.

Pole Pitch between two adjacent poles in case of any machine will always be 180 degrees electrical.

Ques 5. Which of the following compensator will increase the bandwidth of the system:

Phase-Lag

Phase-Lead✓

Lag-lead

None of the above

The general characteristics of phase-lead-compensated systems are as follows:

The high-frequency behavior of a system is improved. This improvement appears as faster responses to inputs, improved rejection of high-frequency disturbances, and reduced sensitivity to changes in the plant parameters.

The system bandwidth is increased, which can increase the response to high-frequency noise in the sensor output signal.

The general characteristics of phase-lag-compensated systems are as follows:

The low-frequency behavior of a system is improved. This improvement appears as reduced errors at low frequencies, improved rejection of low-frequency disturbances, and reduced sensitivity to plant parameters in the low-frequency region.

The system bandwidth is reduced, resulting in a slower system time response and better rejection of high-frequency noise m the sensor output signal.

Ques 6. To increase power transfer capability of a long transmission line, we should

Increase line resistance

Increase transmission voltage

Decrease line reactance

Both (2) & (3)✓

To reduce the power loss in the transmission line the source voltage is stepped up by using the transformer.

By increasing the voltage level the same amount of power can transfer with much smaller current thus reducing transmission line losses (I^{2}R losses).

The power carrying capacity of the line is inversely proportional to the line reactance X therefore by reducing the line reactance we can increase the power carrying capacity.

The system transfer reactance of a transmission line can be reduced by the series capacitance, bundled conductor, or by using parallel transmission line.

Ques 7. The instantaneous voltage and current across a load is given by V = 50 sin (314 t – π/6) volts and I = 10 sin (314t–π/2) amperes, respectively. The active power consumed by the load is

500 watt

1000 watt

125 watt✓

50 watt

Instantaneous Voltage V = 50 sin (314t – π/6) Instantaneous Current I = 10 sin (314t – π/2)

A sinusoidal voltage and current can be described by the equation:

V = V_{M} sin (ωt + Φ) I = I_{m} sin (ωt + Φ)

Hence Peak current and Peak voltage

Im = 10

Vm = 50

Therefore the active power consumed is

Ques 8. Drop in alternator frequency is corrected by:

Damper Winding

Increased Prime Mover Output✓

Automatic Voltage Regulator

None of these

The frequency of an alternator can be adjusted by changing the speed of the Prime Mover as we know that Ns = 120f/P Ns ∝ f Hence the speed of the prime mover is directly proportional to the alternator frequency therefore by increasing the speed of Prime-mover we can increase the speed of an alternator.

Ques 9. In a galvanometer, the deflection becomes one half when the galvanometer is shunted by a 20-ohm resistor. The galvanometer resistance is:

5 ohm

10 ohm✓

40 ohm

20 ohm

The figure given below shows the condition of the problem

Hence

(20 × I)/2 = G/2

G = 20Ω

Ques 10. In a three-phase half wave rectifier feeding resistive load, if the input source is a three phase 4 wire system and line to line voltage is 100 V. The supply frequency is 400 Hz. The ripple frequency at the output is:

400 Hz

800 Hz

1200 Hz✓

1000 Hz

The fig of the above question is shown below

For half-wave rectifier, the ripple frequency is equal to three times the frequency of an A.C supply. i.e

pls upload more previous paper of dmrc with detailed solution

@RAHUL MEENA i will upload more DMRC paper please keep visiting the site

Please provide dmrc je 2017 solved questions and answers

confusion in Q-9 answer.i think misprint or something wrong there.