HSSC-II (12th Class) Physics Unit-16: Alternating Current: Numerical Problems List (Punjab Curriculum and Text Board, Lahore) With Verified Answers

16.1 An alternating current is represented by the equation  I = 20 sin 100 ㄫt. Compute its frequency and the maximum and rms values of current. (Ans :50 Hz, 20 A , 14 A )

 (Click for verified Solution)

16.2 A sinusoidal A .C . has a maximum value of 15 A. What are its rms values? If the time is recorded from the instant the current is zero and is becoming positive, what is the instantaneous value of the current after 1/300 s. given the frequency is 50 Hz. (Ans: `I_{rms}` = 10 .6 A, Instantaneous current = 13.0 A )

 (Click for verified Solution)

16.3 Find the value of the current and inductive reactance when A.C. voltage of 220 V at 50 H z is passed through an inductor of 10 H. (Ans: `I_{rms}` = 0.07 A , `X_L` = 3140 Ω )

(Click for verified Solution)

16.4 A circuit has an inductance of 1/π H and resistance of 2000 Ω. A 50 Hz A.C. is supplied to it. Calculate the reactance and impedance offered by the circuit. (Ans : `\X_L` = 100 Ω, Z = 2002.5 Ω ) 

 (Click for verified Solution)

16.5 An inductor of pure inductance 3/π H is connected in series with a resistance of 40 Ω . Find (i) the peak value of the current (ii) rms value, and (iii) the phase difference between the current and the applied voltage V = 350 sin(100πt). (Ans : (i) 1.16 A, (ii) 0.81 A, (iii) 82 .4° )

 (Click for verified Solution)

16.6 A 10 mH , 20 Ω coil is connected across 240 V and 180/π Hz source. How much power does it dissipate? (Ans: 2778 W ) 

 (Click for verified Solution)

16.7 Find the value of the current flowing through a capacitance 0.5 μF when connected to a source of 150 V at 50 Hz. (Ans: `\I_{rms}` = 0.024 A )

 (Click for verified Solution)

16.8 An alternating source of emf 12 V and frequency 50 Hz is applied to a capacitor of capacitance 3 μF in series with a resistor of resistance 1 kΩ , Calculate the phase angle. (Ans: 46.7°)

 (Click for verified Solution)

16.9 What is the resonant frequency of a circuit which includes a coil of inductance 2.5 H and a capacitance 40 μF? (Ans : 15.9 Hz ) 

(Click for verified Solution)

16.10 An inductor of inductance 150 μH is connected in parallel with a variable capacitor whose capacitance can be changed from 500 pF to 20 pF. Calculate the maximum frequency and minimum frequency for which the circuit can be tuned. (Ans : 2.91 MHz, 0.58 MHz)

 (Click for verified Solution)