Alternating Current

Topics in this chapter

• AC Quantities, RMS, And Power
• Reactance And Phase Relationships
• Series AC Circuits And Phasors
• Resonance, Q-Factor, And Power Factor
• LC Oscillations And Energy
• Transformers And Power Transfer

Cheat sheet

Practice questions

1. Question 1Q-9FE0F5

   An alternating current is given by the equation $I = I_1 \cos(\omega t) + I_2 \sin(\omega t)$. The root mean square (rms) value of this current is:

   1. A.\frac{I_1 + I_2}{\sqrt{2}}
   2. B.\sqrt{\frac{I_1^2 + I_2^2}{2}}
   3. C.\sqrt{\frac{I_1^2 + I_2^2}{\sqrt{2}}}
   4. D.\frac{(I_1 + I_2)^2}{2}
   See the answer and solution
2. Question 2Q-86DDCC

   In a purely inductive circuit connected to an alternating voltage source $V = V_0 \sin(\omega t)$, the current lags behind the voltage by a phase angle of:

   1. A.0
   2. B.\frac{\pi}{4}
   3. C.\frac{\pi}{2}
   4. D.\pi
   See the answer and solution
3. Question 3Q-C6FE9C

   An electric bulb is rated $220\text{ V}, 100\text{ W}$. When it is operated on $110\text{ V}$, the power consumed by the bulb is:

   1. A.100 W
   2. B.50 W
   3. C.25 W
   4. D.200 W
   See the answer and solution
4. Question 4Q-1E9333

   A series LCR circuit containing a resistance $R = 12\;\Omega$, an inductance $L = 0.15\;\text{H}$, and a capacitance $C = 100\;\mu\text{F}$ is connected to a $220\text{ V}, 50\text{ Hz}$ AC source. The impedance of the circuit is approximately:

   1. A.12 \Omega
   2. B.20 \Omega
   3. C.25 \Omega
   4. D.15 \Omega
   See the answer and solution
5. Question 5Q-3074FD

   In a series LCR circuit, the resonant frequency is $f_0$. If both the inductance and capacitance are doubled, the new resonant frequency becomes:

   1. A.2 f_0
   2. B.\frac{f_0}{2}
   3. C.\sqrt{2} f_0
   4. D.\frac{f_0}{\sqrt{2}}
   See the answer and solution