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The correct choice is (d) PHASORS for VOLTAGE and current are in the same direction when the phase angle between voltage and current is zero

The best I can explain: The phasors for voltage and current are in the same direction at all times when the phase angle between voltage and current is zero. All the other statements are not valid. Length of the phasor MUST be equal to the peak VALUE of alternating voltage or alternating current. Also, when the current reaches its MAXIMUM value after emf becomes maximum, then the current is considered to be lagging behind the emf and when the emf reaches its maximum value after current becomes maximum, then the emf is considered to lead the current.

The correct option is (a) 13 A

The explanation is: XL = 2π f L

XL = 2π × 70 × 35 × 10^-3 Ω.

Irms = \(\FRAC {E_{RMS}}{X_L} = \frac {200}{(2\pi \times 70 \times 35 \times 10^{-3})}\)

Irms = 12.99 A ≈ 13 A

Therefore, the rms value of CURRENT in the circuit is 13 A.

The CORRECT answer is (C) K = \(\frac {V_s}{V_p}=\frac {I_p}{I_s}=\frac {N_s}{N_p}\)

Easiest explanation: Transformation ratio (k) is defined as the ratio of number of turns in the secondary winding to the number of turns in the primary winding and the ratio of the current in the primary coil to the current in the secondary coil. It also defined as the ratio of voltage at the secondary terminal to the voltage at the primary terminals. The expression is GIVEN as:

k = \(\frac {V_s}{V_p}=\frac {I_p}{I_s}=\frac {N_s}{N_p}\)

The CORRECT option is (b) 160.3 Ω

Best EXPLANATION: Impedance, Z = √(R^2 + (XL – XC)^2.

Z = √40^2 + (188.4 – 33.17)^2

Z = 160.3 Ω

The correct option is (a) 70.7 A

For EXPLANATION: Irms = 50 A.

I0 = √2 Irms

I0 = 1.414 × 50

I0 = 70.7 A

Therefore, the PEAK current is 70.7 A.

Correct ANSWER is (c) 805 W

For EXPLANATION: Irms = \(\frac {E_{RMS}}{R}\).

Irms = \(\frac {350}{150}\)

Irms = 2.3 A.

Pav = Erms Irms

Pav = 350 × 2.3

Pav = 805 W

The correct answer is (C) A(t) = Amsin⁡(ωt + Φ)

The explanation: A SINUSOIDAL signal is a mathematical curve that describes a smooth periodic oscillation. The general EXPRESSION of a sinusoidal signal is given as FOLLOWS:

A(t) = Amsin⁡(ωt + Φ)

Where➔ Am = Peak Amplitude, ω = Angular Frequency, Φ = PHASE Shift.

Right choice is (d) Electromagnetic induction

The explanation: The working of an a.c. generator is based on the principle of electromagnetic induction. When a coil is rotated about an AXIS PERPENDICULAR to the direction of the uniform magnetic field, an INDUCED emf is produced ACROSS it and hence current is set up in it.

Right answer is (c) Ωm

To EXPLAIN: Capacitive Reactance is the complex impedance of a capacitor whose value CHANGES with respect to the applied frequency. The SI unit of capacitive reactance is the OHM (Ω). Capacitive reactance is denoted by XC.

Right choice is (c) 21 Hz

The best explanation: FR = \(\frac {1}{( 2\pi \SQRT {LC} )}\)

fr = \(\frac {1}{( 2 \times 3.14 \times \sqrt {0.12} \times 0.48 \times 10^{-3} )}\)

fr = 21Hz.

Right answer is (b) Inductive

The EXPLANATION: For a PURELY inductive circuit, Φ = ± \(\FRAC {\pi }{2}\)

Power factor = COS (±\(\frac {\pi }{2}\))

Power factor = 0

Therefore, the power factor will be minimum for an inductive circuit.

Correct option is (c) 4√2 A

For explanation: I = I0 sinωt.

Irms = \(\FRAC {I_0}{\sqrt {2}}\)

Irms = \(\frac {8}{(\sqrt {2})}\)

Irms = 4√2 A

The correct option is (d) 80%

The EXPLANATION: Given: OUTPUT power (Po) = 100 W; Ip = 0.5 A; Vp = 250 V

INPUT power (Pi) = Vp × Ip

Pi = 250 × 0.5 = 125 W

Efficiency = \((\frac {Output \, power}{Input \, power})\) × 100%

Efficiency = \((\frac {100}{125})\) × 100

Efficiency = 80

Therefore, the efficiency of the transformer is 80%.

Correct ANSWER is (b) FALSE

To explain I would say: No, this statement is false. The process of LC OSCILLATIONS, CAUSED when we connect a charged capacitor to an inductor, CONTINUES at a definite frequency. But when the resistance in the LC circuit is zero, the LC oscillations continue at indefinite frequency. Therefore, indefinite frequency is also possible.

Correct option is (c) When a charged capacitor is CONNECTED to an inductor, the electric current in the CIRCUIT and charge on the capacitor undergoes LC oscillations

The explanation is: When we are CONNECTING a charged capacitor to an inductor, the electric current in the circuit and charge on the capacitor undergoes LC oscillations. All the others are incorrect statements regarding LC Oscillations.

The correct OPTION is (b) False

Explanation: When a coil is rotated about an AXIS perpendicular to the DIRECTION of the uniform magnetic field, an induced emf is produced ACROSS it. In an a.c. generator, mechanical ENERGY is converted to electrical energy by electromagnetic induction.

The correct choice is (B) The current that flows through connection wires is called conduction current

For EXPLANATION I WOULD say: The true STATEMENT is ➔ the current that flows through the connection wires is called conduction current. All the other statements are not valid. Displacement current and conduction current can numerically be equal. During charging of the capacitor, in the connection wires, conduction current is continuous and displacement current is discontinuous. SIMILARLY, during the charging of the capacitor, in the gap between the capacitor plates, conduction current is discontinuous and the displacement current is continuous.

Correct answer is (a) True

Explanation: Yes, the EFFICIENCY of a transformer can be determined by taking the ratio of output POWER to input power. Transformers are the most HIGHLY efficient electrical DEVICES. Most of the transformers have full LOAD efficiency between 95% and 98.5%.

Efficiency (η)=\(\frac {Output \, power}{Input \, power}=\frac {V_s I_s}{V_p I_p}\)

The correct choice is (c) 50 Ω

The best I can EXPLAIN: Z = √(R^2 + (XL – XC)^2

Z = √40^2 + (220 – 250)^2

Z = 50 Ω.s

Correct option is (a) 4 A

For EXPLANATION: Xc = \(\FRAC {1}{2πfC}\)

Xc = \(\frac {1}{(2 \times 3.14 \times 80 \times 80 \times 10^{-6})}\)

Xc = 24.8 Ω.

Irms = \(\frac {E_{rms}}{X_C}\)

Irms = \(\frac {100}{24.8}\)

Irms = 4.03 A ≈ 4 A.

Right CHOICE is (d) 223 Hz

The explanation: f = \(\FRAC {X_L}{2\pi L}\)

f = \(\frac {3500}{(2 \times 3.14 \times 2.5)}\)

f = 222.9 Hz ≈ 223 Hz

Therefore, the FREQUENCY of a coil having REACTANCE of 3500 Ω is 223 Hz.

Right CHOICE is (a) 4 A

Explanation: Irms = \(\frac {E_{rms}}{R}\)

Irms = \(\frac {200}{50}\)

Irms = 4 A

The correct choice is (b) 1.44 A

The BEST explanation: e0 = nBAω

e0 = 100 × 0.04 × 3 × 60

e0 = 720 V.

The maximum CURRENT DRAWN = \(\FRAC {e_0}{R} = \frac {720}{500}\)

I = 1.44 A.

The correct choice is (c) ∮\( \overset{\rightharpoonup}{B}.\overset{\rightharpoonup}{dl}\) = μ0 (IC+ID)

To elaborate: The Ampere-Maxwell LAW tells you that this quantity is proportional to the ENCLOSED current and rate of change of ELECTRIC flux through any surface bounded by the PATH of integration. The EXPRESSION for Ampere-Maxwell’s law is given as:

∮\( \overset{\rightharpoonup}{B}.\overset{\rightharpoonup}{dl}\) = μ0(IC+ID)