आधारभूत विद्युत् (Basic Electrical) – Basic Electrical Engineering MCQ
आधारभूत विद्युत् (Basic Electrical) – इलेक्ट्रिकल र टेलिकम
Basic Electrical Engineering · Technical – Electrical, Mechanical & Telecom · २,२९९ प्रश्न
२,२९९ प्रश्न उपलब्ध। मोड छान्नुहोस्:
आधारभूत विद्युत् (Basic Electrical): प्रश्न र उत्तर
सही लागेको विकल्पमा थिच्नुहोस्। सही भए हरियो, गलत भए रातो देखिन्छ; ३ सेकेन्डपछि सही उत्तर र व्याख्या देखिन्छ।
सही: ० / ०
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The magnetising force H required to produce a flux density of 1 T in air is about:
सही उत्तर: घ) 7.96 × 10⁵ A/m
H = B/μ₀ = 1/(4π × 10⁻⁷) ≈ 7.96 × 10⁵ A/m.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A magnetic circuit consists of an iron path of reluctance 4 × 10⁵ AT/Wb in series with an air gap of reluctance 6 × 10⁵ AT/Wb. An mmf of 1000 AT produces a flux of:
सही उत्तर: क) 1 mWb
Series reluctances add: S = 10⁶ AT/Wb, so Φ = F/S = 1000/10⁶ = 1 mWb.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A 4 μF capacitor is connected in parallel with a series pair of 6 μF and 3 μF capacitors. The total capacitance is:
सही उत्तर: ग) 6 μF
6 μF and 3 μF in series give 2 μF; adding 4 μF in parallel gives 6 μF.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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An insulating material has a dielectric strength of 20 kV/mm. With a factor of safety of 2.5, the minimum thickness needed to withstand 50 kV is:
सही उत्तर: घ) 6.25 mm
Allowable stress = 20/2.5 = 8 kV/mm, so thickness = 50/8 = 6.25 mm.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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At the instant a 50 V DC supply is switched onto an uncharged capacitor through a 25 kΩ resistor, the charging current is:
सही उत्तर: ग) 2 mA
An uncharged capacitor initially behaves like a short circuit, so i₀ = V/R = 50/25000 = 2 mA.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The gap of a parallel-plate capacitor (plate area 0.01 m²) is filled with two layers: 2 mm of dielectric with εᵣ = 4 and 3 mm with εᵣ = 6. Its capacitance is about:
सही उत्तर: ख) 88.5 pF
C = ε₀A/(d₁/ε₁ + d₂/ε₂) = 8.854 × 10⁻¹² × 0.01/(0.5 mm + 0.5 mm) = 8.854 × 10⁻¹⁴/10⁻³ ≈ 88.5 pF.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A multi-plate air capacitor has 11 plates, each of effective area 0.01 m², with 1 mm between adjacent plates. Its capacitance is about (ε₀ = 8.854 × 10⁻¹² F/m):
सही उत्तर: क) 885 pF
11 plates form 10 capacitors in parallel: C = 10ε₀A/d = 10 × 8.854 × 10⁻¹² × 0.01/10⁻³ ≈ 885 pF.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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According to Preece's formula, the fusing current of a wire is proportional to d^1.5 (d = diameter). If the diameter is doubled, the fusing current becomes about:
सही उत्तर: ग) 2.83 times
I ∝ d^(3/2); 2^1.5 = 2√2 ≈ 2.83.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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An energy of 5 kWh expressed in megajoules is:
सही उत्तर: घ) 18 MJ
1 kWh = 3.6 MJ, so 5 kWh = 18 MJ.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A motor-pump set lifts 1000 litres of water through 15 m in 10 minutes. The pump efficiency is 70% and the motor efficiency 90%. The electrical input is about (g = 9.81 m/s²):
सही उत्तर: क) 389 W
Water power = 1000 × 9.81 × 15/600 = 245.3 W; input = 245.3/(0.7 × 0.9) ≈ 389 W.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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