Page 412 - Basic Electrical Engineering

23. Explain what is meant by phase and phase difference of alternating quantities.
24. A sinusoidal current is expressed as i = 100 sin 314t. What is the maximum value, RMS value,
frequency, and time period of the alternating current?
25. A sinusoidal voltage, v = 300 sin (314t + 30°) when connected across an ac series circuit
produces a current, i = 20 sin(314t – 30°). What is the power factor of the circuit? Draw the
phasor diagram.
26. Define apparent power, active power, and reactive power of an ac circuit.
27. Define the terms impedance, inductive reactance, capacitive reactance, admittance, active
power, reactive power, and power factor for an ac circuit.
28. Two Z = 10 ∠30° and Z = 20 ∠60° are connected in series. What is the value of
1
2
equivalent impedance?
29. Two impedances Z = 10 ∠30 and Z = 20 ∠30 are connected in parallel. What is the
2
1
equivalent impedance?
30. An impedance of 10 + j10 is connected across a voltage of 230 ∠60° V. What is the
magnitude of current and the value of power factor?
31. Two impedances Z = 10 ∠30° and Z = 10 ∠60°are connected in series. Calculate the
2
1
equivalent impedance.
32. What is resonant frequency? Why is series resonance called voltage resonance?

B. Numerical Problems

33. Calculate the RMS value of an alternating current i= 20(1 + sinθ).

[Ans 24.5 A]

34. Calculate the RMS value of a half-wave-rectified voltage of maximum value of 100 V.

[Ans 50 V]

35. An alternating voltage is expressed as v =141.1 sin 314t. What is the RMS value, time period,
and frequency?

[Ans 100 V, 20 msec, 50 Hz]

36. An alternating current of frequency 50 Hz has its maximum value of 5 A and lagging the
voltage by 30°. Write the equation for the current.

[Ans i = 5 sin (314t - 30°)]

37. An alternating voltage is expressed as, v = 100 sin 314t. Determine the time taken for the
voltage to reach half its maximum value, time counted from t = 0. At what time will voltage
reach its maximum value?