BEE Basic Electrical 5 — Questions and Answers
Question 1: A 60 W lamp operates at 120 V. What is its resistance?
- 240 Ω (Correct answer)
- 7200 Ω
- 0.5 Ω
- 2 Ω
Correct answer: 240 Ω
R = V²/P = (120)²/60 = 14400/60 = 240 Ω.
Question 2: In a star (Y) connected three-phase system, the relationship between line voltage (V_L) and phase voltage (V_ph) is:
- V_L = √3 × V_ph (Correct answer)
- V_L = V_ph
- V_L = 3 × V_ph
- V_L = V_ph / √3
Correct answer: V_L = √3 × V_ph
In a balanced Y connection, the line voltage is √3 times the phase voltage.
Question 3: Which instrument is used to measure electrical energy consumption?
- Energy meter (kWh meter) (Correct answer)
- Wattmeter
- Ammeter
- Voltmeter
Correct answer: Energy meter (kWh meter)
An energy meter (kilowatt-hour meter) integrates power over time to measure total energy consumed.
Question 4: The skin effect in conductors causes current to:
- Concentrate near the surface at high frequencies (Correct answer)
- Distribute uniformly at all frequencies
- Flow only through the core at DC
- Increase with decreasing frequency
Correct answer: Concentrate near the surface at high frequencies
At high frequencies, AC current tends to flow near the conductor's outer surface, reducing the effective cross-sectional area.
Question 5: What is the reactive power in a circuit where V = 100 V, I = 5 A, and the power factor angle θ = 30°?
- 250 VAR (Correct answer)
- 433 W
- 500 VA
- 125 VAR
Correct answer: 250 VAR
Q = V·I·sin θ = 100 × 5 × sin 30° = 500 × 0.5 = 250 VAR.
Question 6: A transformer has 200 primary turns and 50 secondary turns. If the primary voltage is 240 V, what is the secondary voltage?
- 60 V (Correct answer)
- 960 V
- 120 V
- 80 V
Correct answer: 60 V
V2/V1 = N2/N1 → V2 = 240 × (50/200) = 60 V.
Question 7: Which of the following correctly defines 'electric potential difference'?
- Work done per unit charge to move charge between two points (Correct answer)
- Charge per unit time flowing through a conductor
- Energy stored per unit inductance
- Force per unit charge at a point in space
Correct answer: Work done per unit charge to move charge between two points
Potential difference (voltage) is defined as the work done per unit positive charge moved between two points.
BEE Basic Electrical 5
A 60 W lamp operates at 120 V.
What is its resistance?