Quiz: Electrical Engineering 22 July 2020

Quiz: Electrical Engineering
Exam: SSC JE
Topic: Miscellaneous

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

Q1. The breaking capacity of a 3-phase circuit breaker is given by
(a) √3 × service voltage × rated symmetrical current
(b) 3 × service voltage × rated symmetrical current
(c) 2 × service voltage × rated symmetrical current
(d) None of the above

Q2. The insulating material for a cable should have
(a) low cost
(b) high dielectric strength
(c) high mechanical strength
(d) all of the above

Q3. For transfer of maximum power, the relation between load resistance R_L and internal resistance r_i of the voltage source is ……….
(a) R_L=2 R_i
(b) R_L=0.5 R_i
(c) R_L=1.5 R_i
(d) R_L=R_i

Q4. The air gap in a salient pole machine is
(a) Maximum at the centre of poles
(b) Least at the centre of poles and increases while moving away from the centre
(c) Maximum at the centre and decreases while moving away from the centre
(d) Equally distributed

Q5. Hopkinson’s test for DC motor is conducted with
(a) Full load
(b) Half load
(c) Low load
(d) No load

Q6. Tellegen’s theorem is based on the principle of law of _________________.
(a) Conservation of charge
(b) Conservation of mass
(c) Conservation of velocity
(d) conservation of energy

Q7. A D.C. Generator has 6 poles, A brush shift of 6° actual means a brush shift of
(a) 6° electrical
(b) 18° electrical
(c) 30° electrical
(d) 2° electrical

Q8. Full-load terminal voltage in an over-compounded generator with respect to no-load terminal voltage is–
(a) equal
(b) zero
(c) less
(d) more

Q9. Total number of poles and slots in a DC machine are 4 and 8 respectively. Angular slot pitch is ……….
(a) 45 electrical degrees
(b) 90 electrical degrees
(c) 135 electrical degrees
(d) 180 electrical degrees

Q10. In moving Iron type meter has the non-linear scale as:
θ ∝ I_rms
θ ∝ (〖I_rms〗^2)
θ ∝ V_rms
θ ∝ R^2

SOLUTIONS
S1. Ans.(a)
Sol. It is current (rms) that a circuit breaker is capable of breaking at given recovery voltage and under specified conditions.
Breaking capacity = √3 × service voltage × rated symmetrical current

S2. Ans.(d)
Sol. the insulating materials used in cables should have the following properties:
High insulation resistance to avoid leakage current.
High dielectric strength to avoid electrical breakdown of the cable.
High mechanical strength to withstand the mechanical handling of cables.
Non-hygroscopic i.e., it should not absorb moisture from air or soil.
Non-inflammable.
Low cost so as to make the underground system a viable proposition.
Unaffected by acids and alkalis to avoid any chemical action

S3. Ans.(d)
Sol. The maximum power transfer theorem states that in a linear, bilateral DC network, maximum power is delivered to the load when the load resistance is equal to the internal resistance of a source.
If it is an independent voltage source, then its series resistance (internal resistance Rs) or if it is independent current source, then its parallel resistance (internal resistance Rs) must equal to the load resistance RL to deliver maximum power to the load.

S4. Ans.(b)
Sol. Least at the centre of poles and increases while moving away from the centre.

S5. Ans.(a)
Sol. Hopkinson’s test for DC motor is conducted with full load.

S6. Ans.(d)
Sol. Tellegen’s theory is based on conservation of energy.
ie.∑_(K=1)^n▒〖P_k=0 〗
ie,∑_(K=1)^n▒〖I_k×V_K=0 〗
Tellegen’s Theorem states that the summation of power delivered is zero for each branch of any electrical network at any instant of time.

S7. Ans.(b)
Sol. ▭(θ_ele= P/2×θ_mech )
= (6/2)×6
= 18° electrical

S8. Ans.(d)
Sol. so, for over compound full load terminal voltage will be more than No-load voltage.

S9. Ans.(b)
Sol. Slots per pole =8/4=2
Angular slot pitch = (180°)/(slots per pole )
=(180°)/2
=90° (electrical)

S10. Ans.(b)
Sol. In moving Iron type meter, θ ∝ (〖I_rms〗^2)

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