Electromagnetic Induction and Alternating Currents Quiz - ICSE Class 12 Physics

Free practice quiz: Electromagnetic Induction and Alternating Currents (ICSE Class 12 Physics). 44 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

This ICSE Class 12 Physics practice quiz has 44 multiple-choice questions on Electromagnetic Induction and Alternating Currents, and 44 of them come with an explanation. Try the 5 sample questions below (tap an option to check yourself), then play the full quiz online. No sign-up needed.

Sample questions

1. In an AC circuit, the current lags behind the voltage by an angle $\phi$. The power factor of the circuit is given by:

   1. $\sin \phi$
   2. $\tan \phi$
   3. $\cos \phi$
   4. $1/\cos \phi$
   Show answer

   Answer: C. $\cos \phi$

   The power factor in an AC circuit is defined as the cosine of the phase difference between the voltage and the current. It represents the ratio of the real power consumed to the apparent power supplied.

2. A step-down transformer has a turns ratio of 10:1. If the input voltage is 220 V, what is the output voltage?

   1. 2200 V
   2. 22 V
   3. 2.2 V
   4. 440 V
   Show answer

   Answer: B. 22 V

   A step-down transformer decreases voltage. The turns ratio of 10:1 means $N_p/N_s = 10/1$. For an ideal transformer, $V_p/V_s = N_p/N_s$. So, $220 ext{ V} / V_s = 10/1$. This gives $V_s = 220 ext{ V} / 10 = 22$ V.

3. In an AC circuit, the impedance $Z$ of a series RL circuit is given by $Z = \sqrt{R^2 + X_L^2}$. If the frequency of the AC source is increased, the impedance will:

   1. Decrease
   2. Increase
   3. Remain the same
   4. Become zero
   Show answer

   Answer: B. Increase

   The inductive reactance $X_L = 2\pi f L$. Since $L$ and $R$ are constant, if the frequency $f$ increases, $X_L$ increases. As $Z = \sqrt{R^2 + X_L^2}$, an increase in $X_L$ will lead to an increase in $Z$.

4. In a series AC circuit, the impedance is $Z = \sqrt{R^2 + (X_L - X_C)^2}$. If $X_L = 50 \Omega$, $X_C = 30 \Omega$, and $R = 40 \Omega$, the phase angle $\phi$ is:

   1. $\tan^{-1}(1/2)$
   2. $\tan^{-1}(2/3)$
   3. $\tan^{-1}(3/4)$
   4. $\tan^{-1}(4/3)$
   Show answer

   Answer: A. $\tan^{-1}(1/2)$

   The phase angle $\phi$ is given by $\tan \phi = (X_L - X_C)/R$. Substituting the given values, $\tan \phi = (50 \Omega - 30 \Omega) / 40 \Omega = 20 \Omega / 40 \Omega = 1/2$. Therefore, $\phi = \tan^{-1}(1/2)$.

5. A solid iron core is used in a transformer to:

   1. Increase the resistance
   2. Decrease the inductance
   3. Increase the mutual inductance
   4. Reduce the eddy currents
   Show answer

   Answer: C. Increase the mutual inductance

   An iron core has a high magnetic permeability. When placed in a transformer, it concentrates the magnetic field lines, effectively channeling the flux from the primary to the secondary coil. This greatly increases the magnetic flux linkage and thus the mutual inductance between the coils, leading to a more efficient transfer of energy.

More questions in this quiz

Answers and explanations are in the full quiz.

1. A series LCR circuit is connected to an AC source. At resonance, the:
2. The self-inductance of a long solenoid is given by $L = \mu_0 n^2 A l$, where $n$ is the number of turns per unit length, $A$ is the cross-sectional area, and $l$ is the length. If the number of turns is doubled while keeping the length and area constant, the self-inductance will:
3. A transformer is used to step up the voltage from 120 V to 240 V. If the primary coil has 100 turns, how many turns must the secondary coil have?
4. In a pure inductive AC circuit, the current:
5. A coil of resistance $R$ and inductance $L$ is connected to a DC source of voltage $V$. The current at time $t$ is given by $I(t) = (V/R)(1 - e^{-Rt/L})$. The time constant for this circuit is:
6. Which of the following quantities remains constant in a parallel LCR circuit at resonance?
7. Eddy currents are:
8. The rms value of an AC current is defined as the value of DC current which will:
9. Lenz's law is a consequence of the conservation of:
10. The average power consumed in a pure capacitive AC circuit is:
11. A transformer works on the principle of:
12. If the frequency of the AC source supplying a series LCR circuit is doubled, which of the following will increase?
13. The mutual inductance between two coils is $M$. If a current $I$ changes in one coil, the magnetic flux linked with the other coil is proportional to:
14. A series LCR circuit is tuned to resonance. If the frequency of the AC source is increased slightly above resonance, the circuit will behave as:
15. The induced emf in a coil is proportional to:
16. A transformer is designed to operate with maximum efficiency when:
17. The unit of inductance is:
18. In a series AC circuit, the power dissipated is given by $P = V_{rms} I_{rms} \cos \phi$. The term $\cos \phi$ is known as the:
19. A direct current of 5 A flows through a resistor of 10 $\Omega$. The heat produced in 10 seconds is:
20. In a parallel LCR circuit, resonance occurs when:
21. Which of the following statements about eddy currents is INCORRECT?
22. A choke coil is essentially a coil with:
23. If a transformer has an efficiency of 90%, and the input power is 1000 W, the output power is:
24. When is the induced emf in a coil zero?
25. A series AC circuit consists of a resistor $R$, an inductor $L$, and a capacitor $C$. If $R = 10 \Omega$, $X_L = 20 \Omega$, and $X_C = 20 \Omega$, what is the impedance of the circuit?
26. The phenomenon of electromagnetic induction is best demonstrated by:
27. In an AC circuit, a capacitor blocks:
28. A varying magnetic field induces an emf in a conductor because:
29. What is the magnitude of the induced emf in a conductor of length $l$ moving with velocity $v$ perpendicular to a magnetic field of induction $B$?
30. A changing magnetic flux through a loop induces an emf. This statement is a direct consequence of:
31. The ratio of the rms voltage to the rms current in an AC circuit is called the:
32. When a metal disc rotates in a uniform magnetic field, eddy currents are induced in the disc. These eddy currents cause:
33. Which of the following best describes the behavior of a pure inductor in an AC circuit?
34. If the number of turns in the secondary coil of a transformer is increased, while keeping other factors constant, the output voltage will:
35. In an AC circuit, the value of impedance is always:
36. Which component in an AC circuit provides opposition to the flow of current due to its self-inductance?
37. The SI unit of magnetic flux is the:
38. The ratio of secondary voltage to primary voltage in a transformer is equal to the ratio of:
39. The unit of inductive reactance and capacitive reactance is the same as that of:

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