Quiz: Electrical Engineering 14 Sep 2020

Quiz: Electrical Engineering
Topic: Miscellaneous

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. An ammeter is convertible to a voltmeter by
(a) Changing the scale
(b) Putting a large resistance in parallel with the actual measuring part of the instrument
(c) Putting a large resistance in series with the actual measuring part of the instrument
(d) Simply installing the instrument in parallel with the circuit

Q2. What should be the size of the slide wire of the potentiometer to make it to achieve high accuracy?
(a) As long as possible
(b) As short as possible
(c) 1 meter
(d) Neither too thin nor too thick

Q3. Power transformers are designed to have maximum efficiency at
(a) Full load
(b) 50% load
(c) 80% load
(d) no load

Q4. If the field of a DC shunt motor gets opened while the motor is running, then the
(a) Motor will become slow
(b) The motor will attain the dangerously high speed
(c) Armature current will drop
(d) Armature will oscillate about original speed as the mean speed

Q5. In an electric heater, the metal case is connected to…………
(a) Phase wire
(b) earth wire
(c) neutral wire
(d) none of these

Q6. Which of the following is used for heating of non-conducting materials?
(a) Eddy current heating
(b) Arc heating
(c) Dielectric heating
(d) Induction heating

Q7. A high starting torque can be obtained in a 3-phase induction motor by
(a) Increasing Rotor Reactance
(b) Decreasing Rotor Resistance
(c) Increasing Rotor Resistance
(d) Any of the above

Q8. At starting, rotor reactance of a 3-phase induction motor is ………… as compared to rotor resistance.
(a) Small
(b) Equal to
(c) Large
(d) None of the above

Q9. The form factor is the ratio of
(a) Peak value to rms value
(b) Rms value to average value
(c) Average value to rms value
(d) None of the above

Q10. The element which is capable of delivering energy on its own is known as:
(a) Non-Linear elements
(b) Unilateral elements
(c) Active element
(d) Passive element

S1. Ans.(c)
Sol. An ammeter is converted into voltmeter by putting a large resistance in series with the actual measuring part of the instrument.

S2. Ans.(a)
Sol. in case of potentiometer, E ∝ L ⇒ E = φL
Where φ is the potential gradient
So, In the case of longer wire, the fall of potential per unit length is small. In other words, the potential gradient is small. Lesser the potential gradient, more accurate is the potentiometer.

S3. Ans.(a)
Sol. Power transformer are used for transmission as a step-up device hence they are not directly connected to consumer therefore, load fluctuation is very less. So, the power transformer can operate on full load.

S4. Ans.(b)
Sol. N ∝ Eb/φ
Now if the field winding gets open than flux will become zero i.e. φ = 0
∴ N ∝ Eb/0
Or N = ∞
Hence the speed of the DC shunt Motor will attain the dangerous High Seed.

S5. Ans.(b)
Sol. In an electric heater, the metal case is connected to ‘earth wire’ for protection against fault.

S6. Ans.(c)
Sol. Induction heating → for magnetic and conducting materials
Dielectric heating → for non-conducting materials.

S7. Ans.(c)
Sol. in case of induction motor, the starting torque(T) α Rotor resistance.
So, A high starting torque can be obtained in a 3-phase induction motor by increasing rotor resistance.

S8. Ans.(c)
Sol. The rotor resistance does not depend on the slip of the motor. The rotor reactance depends on the slip. At start, the rotor reactance is large because slip of the motor at start is equal to unity. The large rotor reactance at start makes the starting torque of the motor poor. The motor draws about 5 to 6 times current of its full load current and produce very less torque. The most of the current is reactive in nature and does not contribute in production of torque. That is why the starting torque of the squirrel cage induction motor is poor.

S9. Ans.(b)
Sol. The form factor of an alternating current waveform (signal) is the ratio of the RMS (root mean square) value to the average value.

S10. Ans.(c)
Sol. The active elements generate energy. Batteries, generators, operational amplifiers etc are active elements.

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