Quiz: Electrical Engineering 08 Mar 2021

Quiz: Electrical Engineering
Topic: Miscellaneous

Each question carries 1 mark.
Negative marking: 1/3 mark
Time: 10 Minute

Q1. In lap winding, the number of brushes is always…………the number of poles.
(a) Half
(b) Double
(c) Same as
(d) None of the above

Q2. A lap wound DC machine has 400 conductors and 8 poles. The voltage induced per conductor is 2 V. The machine generates a voltage of
(a) 100 V
(b) 200 V
(c) 400 V
(d) 800 V

Q3. The ratio of intensity of magnetization to the magnetization force is known as
(a) Flux density
(b) Susceptibility
(c) Relative permeability
(d) None of the above

Q4. The unit of relative permeability is
(a) Henry
(b) Henry/meter
(c) Henry/sq. meter
(d) It is dimensionless

Q5. The purpose of the conservator in a transformer is
(a) to cool the winding.
(b) to prevent moisture in the transformer.
(c) to prevent short circuit of primary and secondary winding.
(d) to take up contraction and expansion of oil.

Q6. High-voltage d.c. machines use …. winding.
(a) lap
(b) wave
(c) either lap or wave
(d) none of the above

Q7. The arc utilized in electric arc welding is a
(a) High voltage, high current discharge
(b) Low voltage, low current discharge
(c) Low voltage, high current discharge
(d) High voltage, low current discharge

Q8. What will be the reading of megger, if the measuring terminals are open circuited?
(a) 500 Ω
(b) 1000 Ω
(c) Zero
(d) Infinity

Q9. In PMMC instruments, damping torque is provided by:
(a) Eddy currents
(b) Air friction
(c) Fluid friction
(d) Thermal effect

Q10. In 3-phase induction motor the mechanical power developed in terms of air-gap power(Pag) is:
(a) (1-s) Pag
(b) (s-1) Pag
(c) Pag/((1-s))
(d) Pag/s

S1. Ans.(c)
Sol. In a lap winding, the number of parallel paths, A, is always equal to the number of poles, P, and also to the number of brushes. In wave windings, the number of parallel paths, a, is always two (2), and there may be two or more brush positions.

S2. Ans.(a)
Sol. For lap wound, number of parallel path(A)=number of poles(P)
Number of conductors/parallel path = 400/8 = 50
∴Generated voltage = 50 * 2 = 100 V.

S3. Ans.(b)
Sol. In electromagnetism, magnetic susceptibility can also be defined as the measures of how much a material will be magnetized in an applied magnetic field. Mathematically it can be said as the ratio of intensity of magnetisation and magnetizing force.
Where, χ: magnetic susceptibility
M: magnetization
H: field intensity

S4. Ans.(d)
Sol. Relative permeability is the ratio of permeability of the material to the permeability of free space. Since it is a ratio, it is a dimensionless quantity.

S5. Ans.(d)
Sol. Conservator is placed at the top of the transformer. It controls the expansion and contraction of the transformer oil on heating and cooling process respectively.

S6. Ans.(b)
Sol. Wave wound for high voltage & low current whereas LAP winding used for high current and low voltage.

S7. Ans.(c)
Sol. The arc utilized in electric arc welding is a low voltage and high current discharge type.
Arc welding is a type of welding process using an electric arc to create heat to melt and join metals. A power supply creates an electric arc between a consumable or non-consumable electrode and the base material using either direct (DC) or alternating (AC) currents.

S8. Ans.(d)
Sol. When electrical circuit being tested is open, torque due to voltage coil will be maximum and pointer shows ‘infinity’ means no shorting throughout the circuit and has maximum resistance within the circuit under test.

S9. Ans.(a)
Sol. In PMMC instruments, damping torque is provided by eddy currents.

S10. Ans.(a)
Sol. For 3-phase induction motor: Pmech=(1-s) Pag


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