Top 30 Electrical Formula-Based PSC Questions and Equations

 

Most Important Electrical Equations for Kerala PSC, KSEB, Electrician, Overseer & AE Exams

Important Formulas: Ohm’s Law, Power, Energy, Resistance, Series & Parallel Circuits, Transformer Ratio, Frequency, Inductive & Capacitive Reactance.

1. Ohm’s Law

Equation: V = IR

If V = 230 V and R = 46 Ω, find I.

Answer: I = 230 / 46 = 5 A

2. Power Formula

Equation: P = VI

If V = 220 V and I = 5 A, find power.

Answer: P = 220 × 5 = 1100 W

3. Power Using Resistance

Equation: P = I²R

If I = 4 A and R = 10 Ω, find power.

Answer: P = 4² × 10 = 160 W

4. Power Using Voltage

Equation: P = V²/R

If V = 200 V and R = 40 Ω, find power.

Answer: P = 200² / 40 = 1000 W

5. Electrical Energy

Equation: E = Pt

A 1000 W heater operates for 3 hours. Find energy consumed.

Answer: E = 1 kW × 3 h = 3 kWh

6. Resistance Formula

Equation: R = ρL/A

Resistance is directly proportional to length and inversely proportional to area.

PSC Fact: Increasing wire length increases resistance.

7. Series Resistance

Equation: R = R₁ + R₂ + R₃

If resistors are 2 Ω, 3 Ω and 5 Ω, find total resistance.

Answer: 10 Ω

8. Parallel Resistance

Equation: 1/R = 1/R₁ + 1/R₂

If R₁ = 6 Ω and R₂ = 3 Ω, find equivalent resistance.

Answer: 2 Ω

9. Transformer Turns Ratio

Equation: V₂/V₁ = N₂/N₁

If V₁ = 220 V, N₁ = 100, N₂ = 50, find V₂.

Answer: 110 V

10. Frequency Formula

Equation: f = 1/T

If time period T = 0.02 s, find frequency.

Answer: 50 Hz

11. Capacitive Reactance

Equation: Xc = 1/(2πfC)

Reactance decreases with increase in frequency.

PSC Fact: Higher frequency means lower capacitive reactance.

12. Inductive Reactance

Equation: XL = 2πfL

Reactance increases with increase in frequency.

PSC Fact: Higher frequency means higher inductive reactance.

13. Apparent Power

Equation: S = VI

If V = 230 V and I = 10 A, find apparent power.

Answer: 2300 VA

14. Real Power in AC Circuit

Equation: P = VI cosφ

If V = 230 V, I = 5 A and cosφ = 0.8, find power.

Answer: 920 W

15. Efficiency

Equation: η = (Output/Input) × 100

If input = 1000 W and output = 900 W, find efficiency.

Answer: 90%

These equation-based questions are highly useful for Kerala PSC Technical and KSEB examinations.