# Capacitive Reactance

## Trending Questions

**Q.**The frequency for which a 5 μ F capacitor has reactance of 11000Ω is given by

- 106π Hz
- 108π Hz
- 11000Hz
- 1000 Hz

**Q.**A bulb and a capacitor are in series with an ac source. On increasing frequency how will glow of the bulb change

- The bulb quenches
- The glow decreases
- The glow increases
- The glow remain the same

**Q.**An alternating voltage V = 200 sin 100t, where V is in volt and t seconds, is connected to a series combination of 1μ farad capacitor and 10K Ω resistor through an AC ammeter. The reading of the ammeter will be

- √2mA
- 10√2mA
- 2 mA
- 10 mA

**Q.**An AC voltage source, V=200√2 sin100t, is connected across a circuit containing an AC ammeter and capacitor of capacity 1 μF. Reading of the ammeter is:

- 10 mA
- 20 mA
- 40 mA
- 80 mA

**Q.**A bulb and a capacitor are in series with an ac source. On increasing frequency, glow of the bulb

- increases
- decreases
- remains same
- quenches

**Q.**

An alternating voltage E =50 sin(100 t)V is connected to a 1 Î¼F capacitor through an ac ammeter. What will be the reading of the ammeter?

10 mA

5 mA

**Q.**An alternating voltage E=200√2sin(100 t) is connected to a 1 microfarad capacitor through an ac ammeter. The reading of the ammeter shall be

- 10 mA
- 20 mA
- 40 mA
- 80 mA

**Q.**

An arc lamp requires a direct current of 10 A at 80 V to function. If it is connected to a 220 V (rms), 50Hz AC supply, the series inductor needed for it to work is close to:

0.88 H

0.44 H

0.065 H

80 H

**Q.**

How does the $RC$ circuit work?

**Q.**A wire having a linear mass density 5.0×10−3 kg/m is stretched between two rigid supports with tension of 450 N. The wire reasonates at frequency 400 Hz. The next higher frequency at which the wire resonates is 500 Hz. The length of the wire will be

- 1 m
- 4 m
- 4.5 m
- 1.5 m

**Q.**The frequency for which a 5 μ F capacitor has reactance of 11000Ω is given by

- 106π Hz
- 108π Hz
- 11000Hz
- 1000 Hz

**Q.**A capacitor is a perfect insulator for

- Both ac and dc
- Direct currents
- None of these
- Alternating currents

**Q.**What conclusion can you draw from the following observations on a resistor made of alloy manganin?

Current A | Voltage V | Current A | Voltage V |

0.2 | 3.94 | 3.0 | 59.2 |

0.4 | 7.87 | 4.0 | 78.8 |

0.6 | 11.8 | 5.0 | 98.6 |

0.8 | 15.7 | 6.0 | 118.5 |

1.0 | 19.7 | 7.0 | 138.2 |

2.0 | 39.4 | 8.0 | 158.0 |

**Q.**A stretched wire of some length under a tension is vibrating with its fundamental frequency. Its length is decreased by 45% and tension is

increased by 21%. Now its fundamental frequency:

- increases by 50%
- increases by 100%
- decreases by 50%
- decreases by 25%

**Q.**The frequency for which a 5.0μF capacitor has a reactance of 1000Ω is given by:

- 1000π cycles/sec
- 100π cycles/sec
- 200 cycle/s
- 5000 cycles/sec

**Q.**On radiating (sending out) an AM modulated signal, the total radiated power is due to energy carried by ωc, ωc−ωm & ωc+ωm. Suggest ways to minimize cost of radiation without compromising on information.

**Q.**Two alternating voltage generators produce emfs of the same amplitude E0 but with a phase difference of π/3. The resultant emf is:

- E0sin[ωt+(π/6)]
- E0sin[ωt+(π/3)]
- √3E0sin[ωt+(π/6)]
- √3E0sin[ωt+(π/2)]

**Q.**The tuning circuit of a radio receiver has a resistance of 50Ω, an inductor of 10mH and a variable capacitor. A 1MHz radio wave produces a potential difference of 0.1mV. The value of the capacitor to produce resonance is (take π2 =10)

- 2.5pF
- 5.0pF
- 25pF
- 50pF

**Q.**The frequency for which 5μF capacitor has a reactance of 10, 000Ω is

- (100/π) cycles per second
- (10/π) cycles per second
- 200 cycles per second
- 5, 000 cycles per second

**Q.**A coil has an inductance of 0.7H and is joined in series with a resistance of 220 Ω . When an alternating e.m.f. of 220V at 50 c.p.s. is applied to it, then the wattless component of the current in the circuit is

- 0.5 ampere
- 5 ampere
- 7 ampere
- 0.7 ampere

**Q.**An unchanged capacitor is connected in circuit as shown in figure. Power ratings of bulbs are given in diagram. At t=0 switch is closed select correct alternatives :

- At t=0 power consumption in circuit is 3P02
- After a long time power consumption in circuit is P02
- Brightness of B1 decreases with time.
- Initially Brightness of bulb B2 is less than brightness of B1, but later on after certain time B2 will be brighter.

**Q.**An electric bulb and a capacitor are connected in series with an AC source. On increasing the frequency of the source, the brightness of the bulb:

- increase
- decreses
- remains unchanged
- sometime incenses and something decreases

**Q.**A bulb and a capacitor are in series with an ac source. On increasing frequency, glow of the bulb

- increases
- decreases
- remains same
- quenches

**Q.**At a frequency ω0 the reactance of a certain capacitor equals that of a certain inductor. If frequency is changed to 2 ω0 . The ratio of reactance of the inductor to that of the capacitor is

- 4 : 1
- √2:1
- 1:2√2
- 1 : 2

**Q.**A resistor R and 2μF capacitor in series is connected through a switch to 200 V direct supply. Across the capacitor is a neon bulb that lights up at 120 V. Calculate the value of R make the bulb light up 5 s after the switch has been closed (log102.5=0.4).

- 1.3×104Ω
- 1.7×106Ω
- 2.7×106Ω
- 3.3×107Ω

**Q.**An ac source of angular frequency ω is fed across a resistor r and a capacitor C in series. The current registered is I. If now the frequency of source is changed to ω4 (but maintaining the same voltage), the current in then circuit is found to be halved. Calculate the ratio of reactance to resistance at the original frequency ω

- √35
- √25
- √15
- 12

**Q.**The capacitive reactance of a condenser of capacity 25μF for an AC of frequency 4000 Hz will be

- 5πΩ
- 10πΩ
- 5πΩ
- π5Ω

**Q.**An inductance L, a capacitance C and a resistance R may be connected to an AC source of angular frequency ω, in three different combinations of RC, RL and LC in series. Assume that ωL=1ωC. The power drawn by the three combinations are P1, P2, P3 respectively. Then,

- P1=P2=P3
- P1=P2>P3
- P1>P2>P3
- P1=P2<P3

**Q.**In series CR circuit excited by ac mains, C=10μF, R=300Ω. Find the power factor.

Take ν=50 Hz (Standard)

- 3√16
- 3√17
- 3√18
- 3√19

**Q.**When the incident frequency is f0, K is the (KE)max of the electrons emitted and ϕ is the work function of the surface. If incident frequency is doubled, new (KE)max will be

- 2 K−2ϕ
- 2 K
- 2 K+ϕ
- 2 K−ϕ