1. Find the current in the circuit.
a) 10 A
b) 20 A
c) 30 A
d) 40 A
Answer: Option (b)
Explanation:
I=V/R. Total resistance = 20+40=60ohm. I=120V. I=120/60=20A.
2. The resistivity of the conductor depends on
a) area of the conductor.
b) length of the conductor.
c) type of material.
d) none of these.
Answer: Option (c)
Explanation:
The resistivity is a property of material, defined as the resistance between two opposite faces of a cube of a material of unit volume. That is why resistivity is only the unique property of material and it does not depend upon the dimension of any piece of material.
3. The resistance of a conductor of diameter d and length l is R Ω. If the diameter of the conductor is halved and its length is doubled, the resistance will be
a) R Ω
b) 2R Ω
c) 4R Ω
d) 8R Ω
Answer: Option (d)
Explanation:
As per law of resistance, the resistance of the conductor is inversely proportional to its cross-sectional area i.e. it is inversely proportional to the square of the diameter of cross-sectional area of the conductor. As per same law of resistance, the resistance of the conductor is directly proportional to the length of the conductor.
4. How many coulombs of charge flow through a circuit carrying a current of 10 A in 1 minute?
a) 10
b) 60
c) 600
d) 1200
Answer: Option (c)
Explanation:
1 Ampere current means flowing of 1 Coulomb charge per second. That means 10 A current in 1 minute or 60 seconds implies 10 × 60 = 600 coulombs.
5. A capacitor carries a charge of 0.1 C at 5 V. Its capacitance is
a) 0.02 F
b) 0.5 F
c) 0.05 F
d) 0.2 F
Answer: Option (a)
Explanation:
The capacitance of a capacitor is expressed by Q/V. Where Q is the charge of the capacitor and V is the voltage across the capacitor.
6. To obtain a high value of capacitance, the permittivity of dielectric medium should be
a) low
b) zero
c) high
d) unity
Answer: Option (c)
7. Four capacitors each of 40 µF are connected in parallel, the equivalent capacitance of the system will be
a) 160 µF
b) 10 µF
c) 40 µF
d) 5 µF
Answer: Option (a)
Explanation:
The impedance of a capacitor is inversely proportional to its capacitance value. Reciprocal of equivalent impedance of parallel connected circuit elements is sum of reciprocal of impedance of each of the elements.
8. Instantaneous power in inductor is proportional to the
a) product of the instantaneous current and rate of change of current.
b) square of instantaneous current.
c) square of the rate of change of current.
d) temperature of the inductor.
Answer: Option (a)
Explanation:
The instantaneous voltage across the inductor is expressed as the product of inductance and rate of change of current through it. Power is expressed as the product of current and voltage. Hence instantaneous power in an inductor is proportional to the product of instantaneous current and rate of change of current through it.
9. If all the elements in a particular network are linear, then the superposition theorem would hold, when the excitation is
a) DC only
b) AC only
c) Either AC or DC
d) An Impulse
Answer: Option (c)
Explanation:
Superposition theorem can be applied for both AC as well DC excitation to calculate the voltage or current calculations. It holds for both DC and AC excitation, if the circuit is linear. But superposition theorem is not applicable for power calculations.
10. In balanced bridge, if the positions of detector and source are interchanged, the bridge will still remain balanced. This can be explained from which theoem
a) Reciprocity theorem
b) Thevinin's theorem
c) Norton's theorem
d) Compensation theorem
Answer: Option (a)
Explanation:
When response to excitation is constant even though we interchange the excitation and responses then the reciprocity theorem is verified for the given network.
11. If field current is decreased in shunt dc motor, the speed of the motor
a) Remains same.
b) Increases.
c) Decreases.
d) None of the above.
Answer: Option (b)
Explanation:
As a shunt field current If decreases, φ also decreases and the speed rises as speed is inversely proportional to flux.
12. What is the shunt resistance component equivalent circuit obtained by no load test of an induction motor representative of?
a) windage and friction loss
b) core loss only
c) both 1 and 2
d) Copper loss
Answer: Option (b)
Explanation:
No load loss consists of core loss, friction and windage loss and no load copper loss. But shunt branch resistance Rc in the induction motor equivalent circuit does not represent the no load losses, it represents only the core loss of the induction motor.
13. Eddy current loss will depends on
a) Frequency
b) Flux density
c) Thickness
d) All of the above
Answer: Option (d)
14. The emf induced in the dc generator armature winding is
a) AC
b) DC
c) AC and DC
d) None of the above
Answer: Option (a)
Explanation:
The emf induced in the dc generator armature winding is AC, but we need DC current from DC generator, so to convert this AC current to DC current mechanical rectifier called as commutator is used.
15. Commutator in DC generator is used for
a) collecting of current
b) reduce losses
c) increase efficiency
d) convert AC armature current in to DC
Answer: Option (d)
Explanation:
Commutator is used as mechanical rectifier in DC machines. It converts AC armature current in to DC current.
16. Length of the cable is doubled, its capacitance C will be
a) One-fourth.
b) One-half.
c) Doubled.
d) Unchanged.
Answer: Option (c)
Explanation:
The length of the cable and the capacitance of the cable are directly proportional to each other. Hence, if the length gets doubled, then the capacitance also can be doubled.
17. Which of the following rotor is used in thermal power plants?
a) cylindrical rotor
b) salient pole rotor
c) either of these
d) squirrel cage rotor
Answer: Option (a)
Explanation:
Cylindrical rotor is also called as round rotor or smooth rotor, there is no projection, there closed portions contain field winding which is distributed and unslotted portion also acts as poles. It has large axial length and small diameter, resulting high peripheral speed. As the air gap is uniform throughout the machine it is more suitable for high speed operation, employed in all thermal, nuclear power plants containing turbo alternators with two or maximum 4 poles only.
18. Lowest critical frequency is due to pole and it may be present origin or nearer to origin, then it is which type of network?
a) LC
b) RL
c) RC
d) Any of the above
Answer: Option (c)
Explanation:
In RC network lowest critical frequency is due to pole and it is at origin or nearer to origin depending on the value of the capacitance value and transfer function.
19. Which system is also known as automatic control system?
a) open loop control system
b) closed loop control system
c) either 1 or 2
d) nether 1 nor 2
Answer: Option (b)
Explanation:
Control system in which the output has an effect upon the input quantity in order to maintain the desired output value are called closed loop control system. The open loop system can be modified as closed loop system by providing a feedback. The provision of feedback automatically corrects the changes in output due to disturbances. Hence the closed loop control system is also called as automatic control system.
20. By using which of the following elements, mechanical translational systems are obtained?
a) mass element
b) spring element
c) dash-pot
d) all of the above
Answer: Option (d)
Explanation:
The model of mechanical translational systems can be obtained by using three basic elements mass, spring and dash-pot. These three elements represents three essential phenomena which occur in various ways in mechanical systems.
21. Which devices used to measure the temperature of an object?
a) Poteintiometer
b) Odometer
c) Thermometers
d) Galvanometer
Answer: Option (c)
Explanation:
A thermometer is a device that measures temperature or temperature gradient.
22. For audio frequency applications, the popular oscillator used is
a) Wien bridge oscillator
b) Hartley oscillator
c) Crystal oscillator
d) Phase shift oscillator
Answer: Option (a)
Explanation:
Characteristics like ease of tuning, very low distortion and good frequency stability of Wien bridge oscillator makes it becomes popular for audio frequency applications. Phase shift oscillator and Wien bridge oscillator both can be used as audio frequency range. But Wien bridge oscillator can be used for very wide frequency range.
23. Which of the following is not a sinusoidal oscillator?
a) LC oscillator
b) RC phase shift oscillator
c) Relaxation oscillator
d) Crystal oscillator
Answer: Option (c)
Explanation:
Relaxation oscillator is basically a non-sinusoidal oscillator which is used to generate square, triangular or pulse waveforms. The rest of the oscillators are sinusoidal oscillators producing sinusoidal output.
24. Relaxation Voltage controlled oscillators are used to generate
a) Sinusoidal wave
b) Triangular wave
c) Sawtooth wave
d) Both B and C
Answer: Option (d)
Explanation:
Relaxation VCOs can be employed to generate both triangular and saw-tooth waveforms.
25. In an electric room heat converter the method of heating used is
a) Infrared heating.
b) Induction heating.
c) Resistance heating.
d) Arc heating.
Answer: Option (c)
Explanation:
An electric room heat converter is a heater which operates by air covection currents ciculating through the body of the appliacne and across its heating elements. The resistance heating is provided to it. This heats up the air, causing it to increase it to increase in volume and so become buoyant and rise.