The Institution of Engineers,India 2010 A.M.I.E Section A Electrical science summer , - Question Paper
S10: 5 AN: AN 210 (1410)
ELECTRICAL SCIENCE
Time: Three hours
Maximum marks: 100
Q 1. (a) State and explain coulombs law. Define electric field intensity.
(b) A metallic sphere carries a charge. How does electric field and potential vary (i) inside the sphere, (ii) on the surface of sphere, and (iii) outside the sphere?
(c) State and explain Kirchhoffs laws.
Q 2. (a) Differentiate between voltage source and current source.
(b) Use superposition theorem to find current in different branches of the circuit shown in Fig.2:
P 4 O 5 R
/\/\/\/\/
/\/\/\/\/
10 V 6 14 V
S
(c) State and explain Nortons theorem..
Q 3. (a) How can sinusoidal quantities be represented by phasors?
(b) What is meant by the term power factor? Discuss its significance.
(c) An inductive coil takes 10 A and dissipates 1000 W when connected to 250 V, 25 Hz supply. Find impedance, resistance, reactance, inductance, power factor
Q 4. (a) Explain the term phase sequence.
(b) Distinguish between balanced and unbalanced load.
(c) Three loads 31 + j59 ohm, 30 = j40 ohm and 80 + j60 ohm are connected in delta across a 200 V, 3 Phase system. Find phase currents and line currents. Also, find total power.
Group B
Q 5. (a) Draw and explain equivalent circuit of a single-phase transformer.
(b) The primary and secondary winding resistance of a 40 kVA, 660/250 V, single-phase transformer are 10 ohm and 0.02 ohm, respectively. The equivalent leakage reactance, as referred to primary, is 35 ohm. Find full load regulation at load power factors of unity and 0.8 lagging.
Q 6. (a) Differentiate between series and shunt d.e. motors as regards their construction and characteristics.
(b) Name different parts of a d.c. generator.
(c) What is the function of commutators in a d.c. generator?
Q 7. (a) What is meant by the term rotating field?
(b) How are induction motors started?
(c) The power input to rotor of a 3-phase 4-pole 50 Hz induction motor is 100 kW. The full load slip is 0.04. find rotor speed and rotor copper loss.
Q 8. (a) write short notes on the following:
(b) A. C. 3-phase 4-wire distribution.
(c) Starting of single-phase induction motor.
(d) Voltage regulation.
Group C
Q 9. Choose the best alternative for the following:
(i) The electric field intensity at a point situated 4 m from a point charge is 500 NC‹. If the distance is reduced to 2m, the electric field intensity will be
(a) 1000 NC ‹
(b) 2000 NC‹
(c) 250 NC ‹
(d) 125 NC ‹
(ii) An ideal voltage source should have
(a) Zero internal resistance
(b) Infinite internal resistance
(c) Large value of e.m.f.
(d) Low value of e.m.f.
(iii) Tesla is the unit of
(a) Flux
(b) Field strength
(c) Flux density
(d) mmf
(iv) an air gap is usually inserted in magnetic circuits to
(a) increase flux
(b) prevent saturation
(c) increase mmf
(d) decrease flux
(v) if the area of hysteresis loop of a material is large, the hysteresis loss in this material will be
(a) Small
(b) Large
(c) Zero
(d) Small or zero
(vi) The magnitude of statically induces e.m.f. depends on
(a) Magnitude of flux
(b) Rate of change of flux
(c) Resistance of coil
(d) None of the above
(vii) If a capacitor is connected to a.c. source, the current ______ the source voltage by ____.
(a) Lags, 90
(b) Lags, 45
(c) Leads, 90
(d) Leads, 45
(viii) A series RLC circuit has a resonance frequency of 1000 Hz. If the inductance is made 4 times, the resonance frequency will
(a) 1000 Hz
(b) 500 Hz
(c) 707 Hz
(d) 4000 Hz
(ix) At a half power point of a series RLC circuit,
(a) X- Xc = R
(b) X = R
(c) X - Xc = 2R
(d) X- Xc = 0
(x) A 3-phase 4-wire system supplies a balanced star load. The current in each phase wire is 5 A. the current in neutral wire is
(a) 5 A
(b) 5√3 A
(c) 0
(d) 15 A
| Earning: Approval pending. |
