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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Two lamps rated 230 V, 40 W and 230 V, 100 W are connected in series across 230 V. The power drawn by the 40 W lamp is about (resistances assumed constant):
सही उत्तर: क) 20.4 W
R₄₀ = 1322.5 Ω, R₁₀₀ = 529 Ω; I = 230/1851.5 ≈ 0.124 A; P₄₀ = I²R₄₀ ≈ 20.4 W.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In an earth fault, the fault current returns through an earth electrode of 10 Ω and a supply earth of 2 Ω on a 230 V system. The earth-fault current is about:
सही उत्तर: घ) 19 A
I = 230/(10 + 2) ≈ 19.2 A, which may be too small to blow a 32 A fuse quickly; hence the use of RCDs.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A person whose body resistance (hand to feet) is 1 kΩ touches a 230 V live conductor while standing on earth. The current through the body would be about:
सही उत्तर: ग) 230 mA
I = V/R = 230/1000 = 0.23 A = 230 mA, far above the 30 mA trip level of a typical RCCB.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A lamp is moved from 1 m to 3 m directly above a small surface. The illuminance on the surface becomes:
सही उत्तर: ग) 1/9 of its earlier value
By the inverse-square law E ∝ 1/d², so E becomes (1/3)² = 1/9.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A hall 20 m × 10 m is to be lit to 250 lux using 2500 lm lamps, with a utilisation factor of 0.5 and a maintenance factor of 0.8. The number of lamps needed is:
सही उत्तर: क) 50
N = (E × A)/(Φ × UF × MF) = (250 × 200)/(2500 × 0.5 × 0.8) = 50000/1000 = 50.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A luminous flux of 2000 lm falls uniformly on a table of area 4 m². The illuminance on the table is:
सही उत्तर: घ) 500 lux
E = Φ/A = 2000/4 = 500 lux.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A lamp of 400 candela hangs 3 m above a horizontal floor. The illuminance at a floor point 4 m from the point directly below the lamp is:
सही उत्तर: ख) 9.6 lux
Distance = 5 m and cos θ = 3/5: E = I cos θ/d² = 400 × 0.6/25 = 9.6 lux.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The open-circuit emf of a lead-acid cell is about 2 V. How many cells in series are needed for a nominal 24 V battery?
सही उत्तर: क) 12
24/2 = 12 cells in series.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A 24 V, 150 Ah battery bank may be discharged to 70% of its capacity and feeds a 500 W load through an inverter of 90% efficiency. The backup time is about:
सही उत्तर: ख) 4.5 hours
Usable energy = 24 × 150 × 0.7 = 2520 Wh; delivered = 2520 × 0.9 = 2268 Wh; time = 2268/500 ≈ 4.5 h.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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How many 12 V, 100 Ah batteries are needed to form a 48 V, 200 Ah battery bank?
सही उत्तर: ग) 8
4 in series give 48 V, 100 Ah; two such strings in parallel give 200 Ah: 4 × 2 = 8 batteries.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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