Utilization of Electrical Energy, Illumination, Traction and Electric Heating
What the exam tests
Utilization of Electrical Energy covers illumination, electric traction, heating, welding, and electrolysis. MPPSC SES questions test luminous calculations, traction mechanics, and heating element selection.
Core rules
- Illumination: E = Φ/A for uniform flux; inverse-square law E = I/d²; cosine law includes cos θ for inclined surfaces. Utilization factor and maintenance factor reduce installed lumens.
- Luminous efficacy is lumens per watt; LED and sodium lamps exceed incandescent. Glare is controlled by mounting height and louvers.
- Traction: tractive effort Ft = Frolling + Fgradient + Facceleration. Speed–time curves determine energy consumption and schedule speed.
- Electric heating: resistance heating uses I²R; induction heating uses eddy currents; dielectric heating uses high-frequency electric field. Arc furnaces need electrode control.
- Welding: resistance welding depends on I²Rt; arc welding needs drooping characteristic for stable arc.
Worked example
A 20 m × 10 m room requires 300 lux. Coefficient of utilization is 0.5, maintenance factor 0.8, and each lamp gives 3,000 lm. Area = 200 m². Required installed lumens = (300 × 200)/(0.5 × 0.8) = 60,000/0.4 = 150,000 lm. Number of lamps = 150,000/3,000 = 50. Round upward and check spacing-to-mounting-height ratio for uniformity.
Traps
Do not use the inverse-square law without confirming a point source and perpendicular surface. Do not ignore maintenance factor; it raises initial installed lumens. In traction, regenerative braking saves energy only if receptivity exists. In heating, resistance changes with temperature, so cold resistance is not operating resistance.