About this previous year paper
SECTION A (2 Marks Each)
(a) D.C. Arc Heating
D.C. arc heating is a method of heating in which heat is produced by an electric arc formed between electrodes supplied with direct current. It is mainly used in electric arc furnaces for metal melting.
(b) Heating Method Not Dependent on Frequency
Resistance heating is not dependent on the frequency of supply because heat produced depends on current and resistance.
(c) TIG and MIG Welding
TIG (Tungsten Inert Gas) welding uses a non-consumable tungsten electrode, while MIG (Metal Inert Gas) welding uses a consumable metal electrode with shielding gas.
(d) Faraday’s First Law of Electrolysis
The mass of substance deposited at an electrode is directly proportional to the quantity of electricity passed through the electrolyte.
(e) Basic Nature of Light
Light has dual nature, behaving both as a wave and as a particle (photon).
(f) Laws of Illumination
The two laws are Inverse Square Law and Lambert’s Cosine Law.
(g) Speed-Time Curve of Traction System
It shows variation of speed with time and consists of acceleration period, free-running period, coasting, and braking.
(h) Adhesive Weight
Adhesive weight is the portion of locomotive weight available for traction to prevent slipping of wheels.
(i) Traction Systems
Steam traction, diesel electric traction, electric traction, and battery traction.
(j) Diesel Electric Traction
Advantages: no overhead lines, flexible operation.
Disadvantages: higher fuel cost, pollution, lower efficiency.
SECTION B (10 Marks Each – Attempt Any Three)
(a) Ajax Wyatt Furnace
Ajax Wyatt furnace is an induction furnace used for melting metals. It works on the principle of electromagnetic induction where alternating current produces eddy currents in metal, generating heat. It is used in foundries for melting steel and non-ferrous metals.
(b) Electric Resistance Welding
Resistance welding methods include spot welding, seam welding, butt welding, and projection welding. Heat is produced due to resistance at the joint.
Merits over arc welding: high speed, no filler metal, uniform weld.
Demerits: high initial cost, limited thickness.
(c) Illumination Problem
Height of lamp = 10 m
Radius of area = 10 m
Candle power = 800
Maximum illumination (at centre):
Emax = I / h² = 800 / 10² = 8 lux
Minimum illumination (at edge):
Distance = √(10² + 10²) = 14.14 m
Emin = I / d² = 800 / (14.14)² ≈ 4 lux
(d) Systems of Track Electrification
DC system (600 V – 3000 V), single-phase AC system, three-phase AC system, and composite system are used for track electrification.
(e) Suitability of Series Motor for Traction
DC series motors provide high starting torque, variable speed, and good acceleration, making them suitable for traction duties. Speed-torque characteristics favor heavy loads.
SECTION C (10 Marks Each)
Q3
(a) Induction Heating
Induction heating works on electromagnetic induction. Methods include core-type and coreless induction heating.
Applications include metal melting, surface hardening, forging, and welding.
(b) Numerical – Efficiency of Induction Furnace
Heat required:
To raise temperature = m c ΔT = 1.8 × 0.88 × (660 − 150) = 807.84 kJ
Latent heat = 1.8 × 32 = 57.6 kJ
Total heat = 865.44 kJ = 0.24 kWh
Input energy = 4.8 × (10/60) = 0.8 kWh
Efficiency = (0.24 / 0.8) × 100 = 30%
Q4
(a) Arc Welding
Arc welding works by producing heat through an electric arc.
Carbon arc uses carbon electrode, metallic arc uses metal electrode.
DC welding gives stable arc, AC welding is cheaper.
(b) Electro-Deposition
Electro-deposition is the process of depositing metal on a surface using electrolysis. Factors affecting quality include current density, temperature, electrolyte concentration, and voltage.
Q5
(a) Fluorescent Tube
It works on gas discharge principle. Main parts include choke, starter, electrodes, and tube coating. It gives higher efficiency and longer life than incandescent lamps.
(b) Air Conditioning
Air conditioning controls temperature, humidity, purity, and air movement. It depends on heat load, occupancy, climate, and building design.
Q6
(a) Functions of Tractive Effort
Tractive effort is used to overcome train resistance, acceleration, gradient resistance, and braking.
(b) Numerical – Acceleration
Given:
Schedule speed = 30 kmph
Distance = 1 km
Stop time = 20 s
Max speed = 1.25 × 30 = 37.5 kmph
Acceleration required = approximately 1.5 kmphps
Q7
(a) Metadyne Control
Metadyne control uses a rotating amplifier to control traction motor voltage.
Merits: smooth control, high torque.
Demerits: bulky, high maintenance.
(b) Reversal of Traction Motor
Direction is reversed by reversing field or armature current.
Thyristor control advantages include smooth control and high efficiency; disadvantages include harmonics and high cost.