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Right answer is (c) 0°

The BEST I can EXPLAIN: In the CASE of a resistor, the voltage and current are in the same phase. The phase difference between voltage and current is 0°. The voltage drop in the resistor is GIVEN as V=IR.

The CORRECT option is (a) π÷8

Best explanation: SINUSOIDAL waveform is generally EXPRESSED in the form of V=Vmsin(ωt+α) where VM represents PEAK value, ω represents angular frequency, α represents a phase difference.

Right answer is (b) 960 W

For EXPLANATION: USEFUL power is basically the shaft power DEVELOPED by the motor that can be calculated using the formula Psh = Pdev-(rotational losses). Pdev = Pin-Ia^2Ra = 3000-60^2(.4)=1560 W. The useful power developed by the motor is Psh = Pdev-(rotational losses)=1560 –(200+400)=960 W.

Correct choice is (b) STEP up the voltage

The best explanation: Output voltage of boost converter is VO = Vin / 1 – D. Value of duty cycle is less than 1 which makes the Vo > Vin as DENOMINATOR value decreases and becomes less than 1. Boost converter is USED to step up voltage.

Correct ANSWER is (a) Torque is INDEPENDENT of SPEED

Explanation: Speed hoist is a perfect example of constant type loads in which torque variation is independent of speed. The speed-torque characteristics of this type of load are given by T=K where K is a constant.

Right answer is (d) Non-Linearly decreasing TORQUE characteristics

The explanation: Rolling mills are an example of non-linearly decreasing torque characteristics because torque and speed exhibits inversely PROPORTIONAL RELATIONSHIPS and power are constant.

The correct OPTION is (a) .333

Best explanation: Duty CYCLE is Ton÷Ttotal. It is the ratio of time for which the system is ACTIVE and the time taken by the signal to complete one cycle. D= Ton÷Ttotal=5÷15=.333.

The CORRECT ANSWER is (C) 0 Ω

Explanation: The SLOPE of the V-I CURVE is resistance. The slope given is 0° so R=tan(0°)=0 Ω. The slope of the V-I curve is resistance. It behaves as a short circuit.

The correct option is (a) 0 Hz

Explanation: The frequency is defined as the number of OSCILLATIONS per second. It is RECIPROCAL of the time period. DC supply magnitude is CONSTANT. It does not change with time so the frequency of DC supply is 0 Hz.

The correct choice is (b) VA

Easy explanation: The apparent POWER in AC circuits is VI*. It is EXPRESSED in volt-amperes (VA). It CONSISTS of both active and reactive power. It is the VECTOR sum of the real power and reactive power.

Right ANSWER is (B) 0 VAR

Explanation: The resistor is a linear element. It only absorbs real power and dissipates it in the form of heat. The voltage and current are in the same phase in case of the resistor so the angle between V & I is 90°. Q = VIsin0 = 0 VAR.

Correct choice is (d) 1

Explanation: During the resonance condition, the reactive power generated by the CAPACITOR is COMPLETELY ABSORBED by the INDUCTOR. Only active power flows in the circuit. Net reactive power is EQUAL to zero and cosΦ=1.

The correct choice is (a) True

The best explanation: The REACTIVE power is the useless power in CASE of electric circuits. It is the energy trapped that keeps on oscillating between INDUCTIVE and capacitive element. It plays a vital role in GENERATING flux in electrical machines. It is expressed in Volt Ampere reactive.

Correct choice is (a) True

Easy explanation: Salient POLE machines are more stable than cylindrical rotor machines because of the high SHORT circuit ratio and more real power transfer capability. The AIR GAP length in salient pole machines is more as compare to cylindrical rotor machines.

Right option is (a) Eb×Vt×sinδ÷X

For EXPLANATION: The real POWER in the cylindrical rotor MACHINE is Eb×Vt×sinδ÷X. It is inversely PROPORTIONAL to the reactance. The stability of the machine is decided by the maximum power transfer capability.

The correct choice is (a) Ia

Easiest explanation: In a DC shunt MOTOR, the ELECTROMAGNETIC torque developed is equal to KmΦIa. In a DC shunt, the motor field windings are CONNECTED SEPARATELY and EXCITED by a constant DC voltage. T = KmΦIa α Ia.

Right option is (a) 1.732 Ω

For EXPLANATION I would say: The SLOPE of the V-I curve is resistance. The slope given is 90° so R=tan(90°)=INFINITE Ω. It BEHAVES as an open-circuit.

The CORRECT choice is (a) 0.014 SEC

Explanation: The TIME period is DEFINED as the time after the signal repeats itself. It is EXPRESSED in second. T =1÷F=1÷70=.014 sec.

Correct CHOICE is (b) Ia^2

Explanation: In a DC SERIES motor, the electromagnetic torque developed is EQUAL to KmΦIa. In a DC series, the motor field winding is CONNECTED in series with the armature so the flux in the field winding is proportional to CURRENT. T = KmΦIa α Ia^2.

The correct option is (b) 7.300 kgm^2

For EXPLANATION: The moment of inertia of the egg can be CALCULATED USING the formula I=Σmiri^2. The mass of egg and radius is given. I=(12)×(.78)^2=7.300 kgm^2. It depends upon the ORIENTATION of the ROTATIONAL axis.

Correct option is (a) 0.05 Hz

The explanation is: The frequency is defined as the NUMBER of OSCILLATIONS per second. It is reciprocal of the time PERIOD. It is EXPRESSED in Hz. F = 1÷T=1÷20=.05 Hz.

Right option is (b) 17.19 N-m

For explanation I would say: The DEVELOPED torque in the MOTOR is KM×I. The value of MACHINE CONSTANT(Km) is Eb÷ωm = Φ×Z×P÷2×3.14×A = .003×720×4÷2×3.14×4 = .3438 Vs/rad. The developed torque is .3438×50 = 17.19 N-m.

The CORRECT OPTION is (a) 1.732 Ω

Explanation: The slope of the V-I curve is RESISTANCE. The slope GIVEN is 60° so R=tan(60°)=1.732 Ω. The slope of the V-I curve is resistance.

The correct CHOICE is (a) ohm

Easy EXPLANATION: The resistance is the opposition offered by the body to the flow of CURRENT. It is the ratio of VOLTAGE and current. It is GIVEN in ohms.

The CORRECT choice is (d) 1.552 kgm^2

The best I can explain: The moment of inertia of the egg can be calculated USING the formula I=∑miri^2. The mass of egg and RADIUS is GIVEN. I=(7)×(.44)^2=1.552 kgm^2. It depends upon the ORIENTATION of the rotational axis.

Right CHOICE is (c) 240 V

Best explanation: The generated can be calculated using the FORMULA Eb = Φ×Z×N×P÷60×A, Φ represent flux per POLE, Z represents the TOTAL number of conductors, P represents the number of poles, A represents the number of parallel paths, N represents speed in rpm. In lap winding number of parallel paths are EQUAL to the number of poles. Eb = .03×50×400×1200÷60×50= 240 V.

Correct choice is (a) ∑miri^2

Easiest EXPLANATION: The moment of inertia is the property by the VIRTUE of which the BODY withstand the effect of angular acceleration. It DEPENDS on the shape and mass distribution of the body.

Right choice is (a) True

To explain I would SAY: The MOMENT of inertia is taken as the SUM of the product of the MASS of each particle with the square of their distance from the axis of the rotation. The unit of the moment of inertia is kg×m^2=kgm^2.

The correct CHOICE is (b) 90°

The BEST I can EXPLAIN: In the CASE of an inductor, the voltage leads the current by 90° or the current lags the voltage by 90o. The PHASE difference between voltage and current is 90°.

Correct answer is (B) 500 V

Best explanation: The generated can be calculated USING the formula Eb = Φ×Z×N×P÷60×A, Φ represent flux PER pole, Z REPRESENTS the total NUMBER of conductors, P represents the number of poles, A represents the number of parallel paths, N represents speed in rpm. Eb = .02×25×200×600÷60×2= 500 V.

Right OPTION is (d) DC series motor

For explanation I would SAY: DC series motor can OPERATE on DC and AC. It is a universal motor. Universal MOTORS are those motors that can operate on both DC and AC. DC shunt motor can only operate on DC because of pulsating torque in AC.

Correct choice is (b) Magnetic NEUTRAL AXIS (MNA)

To elaborate: The coil UNDERGOING commutation must lie along the magnetic neutral axis so that no emf is induced and there is no sparking at the time of commutation.

The correct answer is (d) THYRISTOR

The explanation: Thyristor is USED for high power APPLICATIONS but it has a limited FREQUENCY range and cannot be used at high frequencies. A thyristor is a UNIDIRECTIONAL, bipolar and semi-controlled device.

Correct OPTION is (c) .083 sec

Best explanation: The fundamental time PERIOD of the sine wave is 2π. The time period of X(t) is 2π÷24π=.083 sec. The time period is independent of PHASE shifting and time shifting.

The correct option is (a) VM÷2^½

To ELABORATE: R.M.S value of the sinusoidal waveform is Vm÷2^½ and r.m.s value of the trapezoidal waveform is Vm÷3^½. The PEAK value of the sinusoidal waveform is Vm.

Right choice is (b) False

Easy EXPLANATION: Angular velocity is defined as the rate of change of angular displacement with respect to TIME. Angular displacement is generally expressed in terms of a RADIAN. The UNIT of angular velocity is rad/s.

Right choice is (a) Speed

The explanation is: The LOAD TORQUE of the crane is independent of speed. They are short time intermittent types of LOADS. They require CONSTANT POWER for a short period of time.

The correct OPTION is (b) Short time loads

The explanation: Servo motors are motors with control feedback. The MOTOR can be AC or DC. This is an EXAMPLE of short time loads. They have a high torque to inertia RATIO and high-speed.

Right answer is (b) 2000 W

Explanation: Shaft power developed by the MOTOR can be CALCULATED using the formula P = Eb*I-(rotational LOSSES) = 50*60 = 3000 – (600+400) = 2000 W. If rotational losses are NEGLECTED, the power developed becomes equal to the shaft power of the motor.

Correct option is (c) SCR

The explanation is: SCR is a minority carrier device due to which it EXPERIENCES conductivity MODULATION and it’s ON state RESISTANCE REDUCTION due to which conduction losses are very low.

Correct choice is (d) Boost converter and BUCK-Boost converter

To elaborate: The OUTPUT voltage of the buck converter and buck-boost converter are Vo=Vin ÷ (1-D) and Vo = D×Vin ÷ (1-D) respectively. When the value of the DUTY CYCLE tends to 1 output voltage tends to INFINITY.