A synchronous motor is switched on to supply with its field windings shorted on themselves. It will
1.not start
2.start but continue to run as an induction motor
3. start as an induction motor and then run as a synchronous motor
4.None of the above
Which of the following is a correct relation?
1.Giga>Mega>Tera
2.Mega>Tera>Giga
3.Tera>Mega>Giga
4. Tera>Giga>Mega
Which of the following is a defined quantity?
1.Pressure
2.Polarity
3.Money
4.Length
A 3 phase, 400 V, 50 Hz salient pole synchronous motor is fed from an infinite bus and is running at no load. Now if the field current of the motor is reduced to zero
1. the motor will stop
2.the motor will run
3. the motor will run at synchronous speed
4. the motor will run at less than synchronous speed
A copper wire of length l and diameter d has potential difference V applied at its two ends. The drift velocity is vd. If the diameter of wire is made d/3, then drift velocity becomes
1.9 vd
2.vd / 9
3.vd /3
4. vd
A synchronous motor is connected to supply voltage V drawing current /. Resultant of v and back emf Eb is represented by E in the figure. From this diagram it can be concluded that
1.power factor it lagging
2.the resultant of V and Eb is consumed by synchronous impedance
3.current I leads the applied voltage by I
4.motor is running on full load
A synchronous motor working on leading power factor and not driving any mechanical, is known
1.synchronous induction motor
2.spinning motor
3.synchronous condenser
4.None of the above
Conductance is expressed in terms of
1.ohm / m
2.m / ohm
3.mho / m
4.mho
Four identical resistors are first connected in parallel and then in series. The resultant resistance of the first combination to the second will be
1.1 / 16 times
2.1 / 4 times
3.4 times
4.16 times
In a synchronous motor if the back emf generated in the armature at no load is approximately equal to the applied voltage, then
1.the torque generated is maximum
2. the excitation is said to be zero percent
3. the excitation is said to be 100%
4.the motor is said to be fully loaded
In case of a synchronous motor we have I. Load II. Speed III. DC excitation The magnitude of stator back emf depends on
1.I only
2. I and II only
3. III only
4. I, II and III
The back emf in the stator of a synchronous motor depends on
1. speed of rotor
2.rotor excitation
3.number of poles
4. flux density
The basic unit for luminous intensity is
1.Ampere
2.Candela
3.Coulomb
4.Radian
The basic unit for luminous intensity is
1.Ampere
2.Candela
3.Coulomb
4.Radian
The purpose of embedding the damper winding in the pole face is to
1.eliminate hunting and provide adequate starting torque
2.reduce windage losses
3. eliminate losses on account of air friction
4.reduce bearing friction
The ratio of the resistance of a 100 W, 220 V lamp to that of a 100 W, 110 V lamp will be nearly
1.4
2.2
3.1 / 2
4.1 / 4
The resistance of a 100 W, 200 V lamp is
1.100 ohm
2.200 ohm
3.400 ohm
4.1600 ohm
Three equal resistors connected in series across a source of emf together dissipate 10 watts of power. What would be the power dissipated in the same resistors when they are connected in parallel across the same source of emf?
1.10 watts
2.30 watts
3. 90 watts
4. 270 watts
Twelve wires of same length and same cross-section are connected in the form of a cube as shown in figure below. If the resistance of each wire is R, then the effective resistance between P and Q will be
1.R
2.5 / 6 R
3. 3 / 4 R
4.4 / 3 R
Two 1 kilo ohm, 1/2 W resistors are connected in series. Their combined resistance value and wattage will be
1.2 kΩ, 1/2 W
2.2 kΩ, 1 W
3.2 kΩ, 2 W
4. l kΩ, 1/2 W
Two resistances R1 and R2 give combined resistance of 4.5 ohms when in series and 1 ohm when in parallel. The resistances are
1.3 ohms and 6 ohms
2.3 ohms and 9 ohms
3.1.5 ohms and 3 ohms
4.1.5 ohms and 0.5 ohms
We have three resistances of values 2 Ω, 3 Ω and 6 Ω. Which of the following combination will give an effective resistance of 4 Ω?
1.All the three resistances in parallel
2.2 Ω resistance in series with parallel combination of 3 Ω and 6 Ω resistance
3.3 Ω resistance in series with parallel combination of 2 Ω and 6 Ω resistance
4.6 Ω resistance in series with parallel combination of 2 Ω and 3 Ω resistance
When P = Power, V = Voltage, I = Current, R = Resistance and G = Conductance, which of the following relation is incorrect?
1. V = √ (PR)
2. P = V2G
3.G = P / I2
4. I = √ (P / R)
Which motor can conveniently operate on lagging as well as leading power factor ?
1.squirrel cage induction motor
2.wound rotor induction motor
3.synchronous motor
4.Any of the above
Which of the following bulbs will have the least resistance ?
1.220 V, 60 W
2. 220 V, 100 W
3.115 V, 60 W
4.115 V, 100 W
Which of the following could be the value of resistivity of copper?
1.1.7 x 10-8 ohm-cm
2.1.7 x 10-6 ohm-cm
3.1.6 x 10-5 ohm-cm
4.1.7 x 10-4 ohm-cm
Which of the following is a correct relation?
1.Giga>Mega>Tera
2.Mega>Tera>Giga
3.Tera>Mega>Giga
4.Tera>Giga>Mega
Which of the following is a defined quantity?
1.Pressure
2.Polarity
3.Money
4.Length
Which of the following motors is non-self starling ?
1.squirrel cage induction motor
2.wound rotor induction motor
3.synchronous motor
4. DC series motor