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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Three identical resistors connected in delta to a three-phase supply consume how many times the power they consume when connected in star to the same supply?
सही उत्तर: ख) 3 times
In delta each resistor gets the line voltage instead of V_L/sqrt 3, so power per resistor (V^2/R) increases 3 times.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Interchanging any two of the three supply lines to a three-phase induction motor:
सही उत्तर: ख) reverses its direction of rotation
Swapping two lines reverses the phase sequence, so the rotating magnetic field turns the other way.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The 'wattless' component of the current in an AC circuit is:
सही उत्तर: ग) I sin phi, the component in quadrature with the voltage
The component at 90 degrees to the voltage produces no average power, so it is called wattless (reactive) current.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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An alternating current is i = 10 sin(100 pi t) amperes. Its value at t = 1/400 s is about:
सही उत्तर: क) 7.07 A
100 pi x 1/400 = pi/4 rad (45 degrees), and 10 sin 45 degrees = 7.07 A.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In a circuit, v = 100 sin(wt) volts and i = 10 cos(wt) amperes. Which statement is correct?
सही उत्तर: क) The current leads the voltage by 90 degrees
cos(wt) = sin(wt + 90 degrees), so the current leads by 90 degrees, as in a pure capacitor.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A series RLC circuit with R = 20 ohm is at resonance across a 100 V supply. The current is:
सही उत्तर: क) 5 A
At resonance X_L cancels X_C, so Z = R and I = 100 / 20 = 5 A.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A 100 kW load operates at 0.6 power factor lagging. The capacitor kVAR needed to raise its power factor to unity is about:
सही उत्तर: ग) 133 kVAR
Q = P tan phi; cos phi = 0.6 gives tan phi = 0.8/0.6 = 4/3, so Q = 100 x 4/3 = 133 kVAR, which must be cancelled.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The imaginary part of the admittance of an AC circuit is called the:
सही उत्तर: घ) susceptance
Admittance Y = G + jB, where G is conductance and B is susceptance, both in siemens.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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If the supply frequency is doubled, the reactance of a pure inductor:
सही उत्तर: घ) doubles
X_L = 2 pi f L, so reactance is directly proportional to frequency.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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At resonance in a series RLC circuit, the voltage across the inductor or the capacitor can be:
सही उत्तर: क) many times greater than the supply voltage
V_L = V_C = Q x V at resonance, so with high Q they can far exceed the supply (voltage magnification).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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