EMI & AC - Electromagnetic Induction
Q. If the magnetic flux through a coil changes from 0.5 Wb to 0.2 Wb in 2 seconds, what is the average induced emf? (2023)
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A.
150 V
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B.
100 V
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C.
75 V
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D.
50 V
Solution
Average induced emf = -ΔΦ/Δt = -(0.2 - 0.5)/2 = 0.15 V = 150 V.
Correct Answer: B — 100 V
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Q. In a transformer, if the primary coil has 100 turns and the secondary coil has 200 turns, what is the turns ratio? (2021)
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A.
1:2
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B.
2:1
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C.
1:1
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D.
3:1
Solution
The turns ratio is 100:200, which simplifies to 1:2.
Correct Answer: A — 1:2
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Q. In an AC circuit, the current lags the voltage by 90 degrees in which of the following components? (2020)
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A.
Resistor
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B.
Capacitor
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C.
Inductor
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D.
Transformer
Solution
In an inductor, the current lags the voltage by 90 degrees.
Correct Answer: C — Inductor
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Q. What is the effect of increasing the frequency of the AC supply on the inductive reactance? (2020)
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A.
Increases
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B.
Decreases
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C.
Remains constant
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D.
Becomes zero
Solution
Inductive reactance increases with frequency, as X_L = 2πfL.
Correct Answer: A — Increases
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Q. What is the reactance of an inductor at a frequency of 50 Hz if the inductance is 0.1 H? (2023)
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A.
31.4 Ω
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B.
6.28 Ω
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C.
157 Ω
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D.
12.56 Ω
Solution
Reactance (X_L) = 2πfL = 2π(50)(0.1) = 31.4 Ω.
Correct Answer: A — 31.4 Ω
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Q. Which of the following is a practical application of electromagnetic induction? (2019)
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A.
Electric generator
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B.
Resistor
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C.
Capacitor
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D.
Diode
Solution
Electric generators utilize electromagnetic induction to convert mechanical energy into electrical energy.
Correct Answer: A — Electric generator
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