# Phasor

## Trending Questions

**Q.**

A coil of inductance 0.50 H and resistance 100 Ω is connected to a 240 V, 50 Hz ac supply.

(a) What is the maximum current in the coil?

(b) What is the time lag between the voltage maximum and the current maximum?

**Q.**A resistance of 50Ω, an inductance of 20π H and a capacitor of 5πμF are connected in series with an A.C. source of 230 volts and 50 Hz .The impedance of circuit is_______(in ohm)

**Q.**At very high frequencies, the effective impedance of the given circuit will be ________ \(\Omega \).

10 O05F 20 OS5F I AMW— | AMW— J—D.SF 10 20H 20 OS5F 220V

**Q.**A transistor-oscillator using a resonant circuit with an inductor L ( of negligible resistance ) and a capacitor C in series produce oscillations of frequency f. If L is doubled and C is changed to 4C, the frequency will be

- f4
- f2√2
- f2
- f8

**Q.**With increase in frequency of an AC supply, the impedance of an LCR series circuit

- Remains constant
- Decreases
- Increases
- Decreases at first, becomes minimum and then increases.

**Q.**For the circuit shown in below figure, current in the inductor is 0.8 A while in the capacitor is 0.6 A. What is the current drawn from the source?

- 0.3 A
- 0.1 A
- 0.6 A
- 0.2 A

**Q.**1. In an A.C circuit with an inductor and a resistor, current leads source voltage.

2. In an R.L.C circuit, current may lead source voltage.

3. In an A.C circuit with a capacitor and a resistor, current leads source voltage.

4. Up on increasing the frequency of a source, power factor decreases.

- All statements are true.
- 2 and 3 are true.
- 2, 3 and 4 are true.
- 1 and 4 are true.

**Q.**A 12 Ω resistance and an inductance of 0.05π H with negligible resistance are connected in series. Across the ends of this circuit a 130 V alternating voltage of frequency 50 Hz is connected. Calculate the alternating current in the circuit and the potential difference across the resistance.

- 10 A, 50 V
- 10 A, 120 V
- 5 A, 60 V
- 5 A, 120 V

**Q.**A 0.07 H inductor and a 12 Ω resistor are connected in series to a 220 V, 50 Hz ac source. The approximate current in the circuit and the phase angle between current and source voltage are respectively. [Take π as 227]

- 0.88 A and tan−1(116)
- 88 A and tan−1(116)
- 8.8 A and tan−1(116)
- 8.8 A and tan−1(611)

**Q.**An AC circuit consists of an inductor of inductance 0.5 H and a capacitor of capacitance 8 μF in series. The current in the circuit is maximum, when the angular frequency of the source is -

Impedance for AC LC circuit is given by Z=|XL−XC|.

- 500 rad/s
- 600 rad/s
- 700 rad/s
- 800 rad/s

**Q.**In an AC circuit, the impedance is √3 times the reactance, then the phase angle is -

- 60∘
- 30∘
- 45∘
- sin−1(1√3)

**Q.**Consider the following AC RLC circuit. The maximum voltage drop across the inductor is -

- 17.5 V
- 15.5 V
- 12.5 V
- 19.5 V

**Q.**In the following AC circuit the emf of source is E0=200 V, R=20 Ω, L=0.1 H, C=10.6 F and frequency is variable, then the current at frequency f=0 and f=∞ are

- Zero, 10 A
- 10 A, Zero
- 10 A, 10 A
- Zero, Zero

**Q.**The graphs given below depict the dependence of two reactive impedance X1 and X2 on the frequency of the alternating e.m.f. applied individually to them, we can then say that-

- X1 is an inductor and X2 is a resistor.
- X1 is a capacitor and X2 is an inductor.
- X1 is a resistor and X2 is a capacitor.
- X1 is an inductor and X2 is a capacitor.

**Q.**In an AC series circuit, the instantaneous current is zero when the instantaneous voltage is maximum. Connected to the source may be a

- Pure inductor
- Pure capacitor
- Pure resistor
- combination of an inductor and a capacitor

**Q.**A series circuit has a resistance of 60 Ω and an impedance of 135 Ω. When the total potential difference is 120 V, the power consumed in the circuit is x W. The value of x is ________.

[Round off to the nearest odd integer]

**Q.**Corresponding to the figure shown, match the two columns.

Column I | Column II |

a. Resistance b. Capacitive reactance c. Inductive reactance d. Impedance |
p. 4 q. 1 r. 2 s. 3 |

- a→s; b→p; c→r; d→q
- a→p; b→s; c→r; d→q
- a→s; b→p; c→q; d→r
- a→q; b→p; c→r; d→s

**Q.**A diode detector is used to detect an amplitude modulated wave of 60% modulation by using a condenser of capacity 250 pico farad in parallel with a load resistance 100 kilo ohm. Find the maximum modulated frequency which could be detected by it.

- 5.31 kHz
- 10.62 MHz
- 10.62 kHz
- 5.31 MHz

**Q.**A series LCR circuit is connected across an AC supply of frequency f. The resonant frequency of the circuit is fr. The current will lag behind the voltage when -

- f=0
- f=fr
- f>fr
- f<fr

**Q.**A 12 Ω resistor and an inductor of 0.05π H with negligible resistance are connected in series. Across this combination, an alternating voltage of 130 V, 50 Hz is connected. Calculate the rms value of alternating current in the circuit.

- 10 A
- 15 A
- 18 A
- 12 A

**Q.**In a series RC circuit shown in the figure, at an instant, the applied voltage is 10 V and the voltage across the capacitor is found to be 8 V. The phase difference between the current and the applied voltage will be -

- tan−1(43)
- tan−1(34)
- tan−1(53)
- tan−1(35)

**Q.**In the given circuit, the AC source has angular frequency ω=100 rad s−1. Considering the inductor and capacitor to be ideal, what will be the current I flowing through the circuit ?

- 0.94 A
- 6 A
- 3.16 A
- 4.24 A

**Q.**An AC circuit contains a resistor of 10 Ω and an inductor of 2.0 H, joined in series. If an AC voltage source of 120 V, 60 Hz is applied across this circuit, the peak AC will be -

- 0.52 A
- 0.42 A
- 0.22 A
- 0.32 A

**Q.**In an AC circuit, the reactive impedance is √3 times the R. Then, the power factor is

- √32
- 12
- 1√2
- 1√3

**Q.**A wire of length 10 km has a capacitance of 0.014 μF per meter. If it carries an AC of frequency 70 Hz, then what should be the value of the inductance of the inductor required to be connected in series with it, so that the impedance of the circuit is minimum?

Take π2≈10

- 0.36 mH
- 36 mH
- 3.6 mH
- Zero

**Q.**Draw the circuit symbol of n−p−n transistor.

**Q.**Find the value of an inductance (in H) which should be connected in series with a capacitor of 5 μF, a resistance of 10 Ω and a source of 50/π Hz so that the power factor of the circuit is unity.

**Q.**

A coil of inductance 0.50 H and resistance 100Ω is connected to a 240 V, 50 Hz ac supply.

(a) What is the maximum current in the coil?

(b) What is the time lag between the voltage maximum and the current maximum?

Hence, explain the statement that at very high frequency, an inductor in a circuit nearly amounts to an open circuit. How does an inductor behave in a dc circuit after the steady state?

**Q.**In a series L-C-R circuit, voltage across resistor, capacitor and inductor is 20V each. If capacitor is short circuited the voltage across inductor is?

- 10√2V
- 20√2V
- 5√2V
- 5√2V

**Q.**An alternating L−C−R circuit is shown in figure, then match the column : (Here symbols have their usual meaning)

Column-I Column-II

(A). If ωL1−1C1ω=R1, and ωL2−1ωC2=R2 | (1). I1 and I2 are in same Phase. |

(B). If ωL1−1C1ω=R1, and 1ωC2−ωL2=R2 | (2). I=I1+I2 where , I1 , I2 , I3 are RMS value of currents. |

(C). If capacitor C1 and inductor L2 are removed from circuit and ωL1=R1 ; 1ωC2=R2 | (3). Magnitude of phase difference between I1 and I2 is π2 |

(D). If capacitors C1 and C2 are both removed from the circuit and ωL1=R1 ; ωL2=R2 | (4). I=√(I1)2+(I2)2 where, I1 , I2 , I3 are RMS value of currents. |

(5). I1 is lags and I2 is leads from source voltage. |

- (A)→(1, 2) ; (B)→(3, 4, 5) ; (C)→(3, 4, 5) ; (D)→(1, 2)
- (A)→(1, 4) ; (B)→(3, 5) ; (C)→(3, 5) ; (D)→(1, 2)
- (A)→(1, 4) ; (B)→(3, 4) ; (C)→(3, 4) ; (D)→(1, 4)
- (A)→(1, 2) ; (B)→(3, 4, 5) ; (C)→(3, 4, 5) ; (D)→(1, 4)