Q6. A. What are the characteristics of PN junction diode? Point out its specifications. Also point out the significance of dynamic and static resistances.
B. Draw the circuit of Half-wave rectifier and its output waveform. A diode whose internal resistance is 20 is to supply power to 1000 load from 110 V (RMS) source. Calculate
(i) peak load current, (ii) DC load current, (iii) AC load current.
Q7. With reference to adjoining circuit calculate following. (a) Current in each branch of circuit. (b) Total current.
Q7. A. Describe how protection against short circuit is provided in a 3 phase induction motor circuit.
B. Explain how rotating magnetic field is produced in three phase winding with three phase supply. A 4-pole, 3-phase induction motor operates from a supply whose frequency is 50 Hz. Calculate
(i) Speed at which the magnetic field of the stator is rotating,
(ii) speed of the rotor when the slip is 0.04,
(iii) the frequency of the rotor current when the slip is 0.03.
Q10. A. How does change to frequency affect the operation of the transformer? What makes this ratio different from the ratio of transformer? B. A 550 KVA, 50 Hz single phase transformer has 1875 and 75 turns in the primary and secondary windings respectively. If the secondary voltage is 220 V, calculate (i)Primary voltage; (ii)Primary and secondary currents; iii. Maximum value of flux.
Q8. The armature and filed resistances of a 220 V shunt motor are 0.25 ohm and 110 ohm respectively and when running on load, the motor takes 6 A. Calculate the losses attributable to iron, friction and windage and assuming this value to remain constant on loads, determine the efficiency when the current supplied is 62 A.
Q9. (a) Define longitudinal centre of gravity (LCG) and longitudinal centre of buoyancy (LCB). (6)
(b) The immersed cross-sectional areas of a ship 120m long, commencing from aft are 2, 40, 79, 100, 103, 104, 104, 103, 97, 58 and 0 m2. Calculate:
(i) Displacement
(ii) Longitudinal position of the centre of buoyancy. (10)
Q9. A) Describe the effect of cavitations on the propeller blades. (6)
B) A propeller 4.6m diameter has a pitch of 4.3m and boss diameter of 0.75 m. The real slip is 28% at 95 rev/min. Calculate the speed of advance, thrust and thrust power. (10)
Q8. A ship of 9,900 tonnes displacement has KM=7.3 m and KG=6.4 m she has yet to load two 50 tonne lifts with her own gear and the first lift is to be placed on deck on the inshore side (KG 9 m and center of gravity 6m out from the center line). When the derrick plumbs the quay its head is 15m above the keel an 12m out from the center line.
Calculate the maximum list during operation.
Q8. A. Explain the reasons for fitting bulbous bow. B. When a ship is 800 nautical miles from port its speed is reduced by 20%, thereby reducing the daily fuel consumption by 42 tonne and arriving in port with 50 tonne on board. If the fuel consumption in t/h is given by the expression (0.136+0.001 V3) where V is the speed in knots, estimate: (i) The reduced consumption per day; (ii) The amount of fuel on board when the speed was reduced; (iii) The percentage decrease in consumption for the latter part of the voyage;
(iv) The percentage increases in time for this latter period.
Q6. Describe the movement of a ship with negative metacentric height B. A ship of 8000 tonne displacement has its centre of gravity 4.5m above the keel and transverse metacenter 5.0m above the keel when a rectangular tank 7.5m long and 15m wide contains seawater. A mass of 10 tonne is moved 12m across the deck. Calculate the angle of heel i. If there is free surface of water ii. If the water doesn’t completely fill the tank.
Q10. A. Explain the considerations which govern the size and shape of a rudder. B. A ship of 12000 tonne displacement has a rudder 15m2 in area, whose centre is 5m below the waterline. The metacentric height of the ship is 0.3m and the centre of buoyancy is 3.3m below the waterline. When travelling at 20 knots the rudder is turned through 30 . Find the initial angle of heel if the force Fn perpendicular to the plane of the rudder is given by: Fa=577 Av2 sin N, Allow 20% for the race effect.
Q8. A. Describe the ways in which an unstable ship can be made stable. B. When a mass of 25 tonnes is shifted 15m transversely across the deck of a ship of 8,000 tonnes displacement, it causes a deflection of 20cms in a plumb line 4m long. If the KM=7 m, calculate the KG
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