Engineering Discipline (Civil / Electrical / Mechanical / Agriculture) - Technical Subject
Engineering Discipline (Civil/Electrical/Mechanical/Agriculture) is the technical core. The candidate normally answers one branch, but basic engineering science overlaps. Focus on definitions, units, standard formulae and field applications.
Branch essentials
- Civil: stress = force/area, strain = change/length, Young's modulus = stress/strain; concrete grade M20 means 20 N/mm² characteristic strength; surveying levels, contour and levelling; water demand and irrigation.
- Electrical: Ohm's law V=IR; power P=VI; three-phase power P=√3 V_L I_L cosφ; transformer principle is mutual induction; earthing is for safety.
- Mechanical: first law of thermodynamics; efficiency = output/input; SFD/BMD for beams; gear ratio = N1/N2; IC engine four strokes.
- Agriculture: soil texture, pH, NPK, irrigation scheduling, seed rate and farm power.
Worked example
A 12 V battery is connected across a 4 Ω resistor. Current I = V/R = 12/4 = 3 A. Power P = VI = 12 × 3 = 36 W, or I²R = 9 × 4 = 36 W. If the resistor is replaced by 6 Ω, current falls to 2 A and power to 24 W, showing the inverse relation between resistance and current at fixed voltage.
Traps
Keep units consistent: mm² vs m², kW vs W. In AC, power factor matters; apparent power is not real power. In concrete, nominal mix and design mix are not interchangeable. In thermodynamics, gauge and absolute pressure differ by atmospheric pressure. In agriculture, do not confuse N, P, K percentages with fertiliser weight.