Grade 12 : Physics - Alternating Current (Set 2)

Question 1

An alternating voltage source delivers a peak voltage of $V_0 = 200 ext{ V}$ to a circuit.

What is the RMS (root mean square) value of the voltage?

Accepted Answer

B) 141.4 V

Answer

A) 100 V

Answer

C) 200 V

Answer

D) 282.8 V

Question 2

In a purely capacitive AC circuit, what is the phase relationship between current and voltage?

Accepted Answer

C) Current leads voltage by $\pi/2$ radians

Answer

A) Voltage and current are in phase

Answer

B) Voltage leads current by $\pi/2$ radians

Answer

D) Current leads voltage by $\pi$ radians

Question 3

How does the inductive reactance $X_L$ of an inductor vary with the supply frequency $f$?

Accepted Answer

B) Directly proportional to frequency

Answer

A) Inversely proportional to frequency

Answer

C) Independent of frequency

Answer

D) Proportional to the square of frequency

Question 4

What is the reactance of a capacitor in a Direct Current (DC) circuit ($f = 0$)?

Accepted Answer

C) Infinite

Answer

A) Zero

Answer

B) Equal to its capacitance

Answer

D) Depends on resistance

Question 5

A series LCR circuit contains an inductor $L$, capacitor $C$, and resistor $R$ connected to an AC source.

At electrical resonance, what is the total impedance $Z$ of the circuit?

Accepted Answer

D) $R$

Answer

A) Zero

Answer

B) $X_L - X_C$

Answer

C) $\sqrt{R^2 + X_L^2}$

Question 6

Which basic electromagnetic phenomenon forms the working principle of a transformer?

Accepted Answer

B) Mutual induction

Answer

A) Self induction

Answer

C) Seebeck effect

Answer

D) Peltier effect

Question 7

An AC current source produces a maximum peak current of $I_0 = 10 ext{ A}$.

What is the root-mean-square (RMS) current $I_{rms}$ flowing through the circuit?

Accepted Answer

B) 7.07 A

Answer

A) 5.00 A

Answer

C) 10.00 A

Answer

D) 14.14 A

Question 8

What is the average power dissipated per full cycle in a purely inductive circuit?

Accepted Answer

A) Zero

Answer

B) $V_{rms} I_{rms}$

Answer

C) $\frac{1}{2} V_{rms} I_{rms}$

Answer

D) $V_0 I_0$

Question 9

For an ideal step-up transformer, how does the secondary turns ratio ($N_s / N_p$) compare to 1?

Accepted Answer

C) Greater than 1

Answer

A) Less than 1

Answer

B) Equal to 1

Answer

D) Zero

Question 10

What is the power factor ($\cos\phi$) of a purely resistive AC circuit?

Accepted Answer

C) 1

Answer

A) 0

Answer

B) 0.5

Answer

D) $\sqrt{2}$

Question 11

Which formula correctly gives the resonant angular frequency $\omega_0$ of a series LCR circuit?

Accepted Answer

B) $\frac{1}{\sqrt{LC}}$

Answer

A) $\sqrt{LC}$

Answer

C) $\frac{L}{C}$

Answer

D) $\frac{1}{LC}$

Question 12

What is the mean (average) value of alternating current over a positive half-cycle in terms of peak current $I_0$?

Accepted Answer

C) $\frac{2 I_0}{\pi}$

Answer

A) $\frac{I_0}{2}$

Answer

B) $\frac{I_0}{\pi}$

Answer

D) $\sqrt{2} I_0$

Question 13

What is the SI unit of capacitive reactance $X_C$?

Accepted Answer

C) Ohm

Answer

A) Farad

Answer

B) Henry

Answer

D) Hertz

Question 14

A series LCR circuit has resistance $R = 30\,\Omega$, inductive reactance $X_L = 80\,\Omega$, and capacitive reactance $X_C = 40\,\Omega$.

What is the total impedance $Z$ of the circuit?

Accepted Answer

B) $50\,\Omega$

Answer

A) $30\,\Omega$

Answer

C) $70\,\Omega$

Answer

D) $150\,\Omega$

Question 15

What is the standard frequency of alternating current supply used in domestic households in India?

Accepted Answer

B) 50 Hz

Answer

A) 25 Hz

Answer

C) 60 Hz

Answer

D) 100 Hz

Question 16

What name is given to current flowing in an AC circuit when the power factor is zero?

Accepted Answer

B) Wattless current

Answer

A) Peak current

Answer

C) Virtual current

Answer

D) Direct current

Question 17

Which expression defines the Quality Factor ($Q$-factor) of a series resonant LCR circuit?

Accepted Answer

A) $\frac{\omega_0 L}{R}$

Answer

B) $\frac{\omega_0 R}{L}$

Answer

C) $\frac{R}{\omega_0 L}$

Answer

D) $\frac{1}{\omega_0 L R}$

Question 18

In an AC circuit, the power factor $\cos\phi$ is defined as the ratio of:

Accepted Answer

A) Resistance to Impedance ($R/Z$)

Answer

B) Reactance to Resistance ($X/R$)

Answer

C) Impedance to Resistance ($Z/R$)

Answer

D) Voltage to Current ($V/I$)

Question 19

An alternating voltage is represented by the equation $V = 100 \sin(100\pi t)$ volts.

What is the angular frequency $\omega$ of the alternating voltage?

Accepted Answer

C) $100\pi	ext{ rad/s}$

Answer

A) 50 rad/s

Answer

B) 100 rad/s

Answer

D) $200\pi	ext{ rad/s}$

Question 20

Why is the iron core of a transformer laminated?

Accepted Answer

C) To reduce energy loss due to eddy currents

Answer

A) To reduce hysteresis loss

Answer

B) To reduce copper loss in windings

Answer

D) To prevent magnetic flux leakage