# Power Factor

## Trending Questions

**Q.**

In a series $LR$ circuit, power of $400W$ is dissipated from a source of $250V,50Hz$. The power factor of the circuit is $0.8$. In order to bring the power factor to unity, a capacitor of value $C$ is added in series to the $L$ and $R$. Taking the value of $C$ as $\left(\frac{n}{3\mathrm{\pi}}\right)\mu F$, then the value of $n$ is __________.

**Q.**The potential differences across the resistance, capacitance and inductance are 80 V, 40 V and 100 V respectively in an L-C-R circuit. The power factor of this circuit is

- 0.8
- 1.0
- 0.4
- 0.5

**Q.**

A transformer has an efficiency of $80\%$. It is connected to a power input of $5kW$ at $200V$. If the secondary voltage is $250V$, the primary and secondary currents are respectively

$25A$, $20A$

$20A$, $16A$

$25A$, $16A$

$40A$, $25A$

$40A$, $16A$

**Q.**

What are the applications of transformers?

**Q.**

. The phase difference between the current through the resistance and voltage across the resistance in a series LCR circuit is

**Q.**

A sinusoidal voltage of peak value $250V$ is applied to a series $LCR$ circuit, in which $R=8\Omega $, $L=24mH$ and$C=60\mu F$. The value of power dissipated at resonant conditions is $xkW$. The value of$x$ to the nearest integer is _________.

**Q.**

Obtain the resonant
frequency *ω**r *of
a series *LCR *circuit with *L *= 2.0 H, *C *= 32 μF
and *R *= 10 Ω. What is
the *Q*-value of this circuit?

**Q.**In an ac circuit, the instantaneous values of e.m.f. and current are e = 200 sin 314 t volt and i=sin(314t+π3) ampere. The average power consumed in watt is

- 200
- 100
- 50
- 25

**Q.**

What is the maximum current that can be drawn from a cell of emf E and internal resistance r connected to an external resistance R?

I = E/R

I = E/(R+r)

I = E/r

infinite

**Q.**

A current of 5A is flowing at 220V in the primary coil of a transformer. If the voltage produced in the secondary coil is 220V and 50% of power is lost, then the current in secondary will be:

0.5A

2.5A

5A

0.25A

**Q.**

The plot given below is of the average power delivered to an LRC circuit versus frequency. The quality factor of the circuit is:

5

2

2.5

4, 0

**Q.**If power factor is 12 in a series RL circuit R = 100Ω. AC mains is used then L is

- None of these
- πHenry

**Q.**The series combination of resistance R and inductance L is connected to an alternating source of e.m.f. E=311sin(100πt). If the peak value of wattless current is 0.5 A and the impedance of the circuit is 311 Ω, the power factor will be

- 12
- √32
- 1√3
- 1√5

**Q.**

The change in magnetic field lines in a coil is the cause of induced electric current in it. Name the underlying phenomenon.

**Q.**If a fan of 60 W, two tube lights of 40 W each are used for 5 hours daily, how much electrical energy willbe consumed? Also find the cost of electricity for 30 days if the cost of 1 unit is Rs. 4 00

**Q.**The power factor of LCR circuit at resonance is

- 0.707
- 1
- Zero
- 0.5

**Q.**A magnet is suspended from a spring as shown in the diagram. When it oscillates, the magnet moves in and out of the coil. The coil is connected to a galvanometer G. Then, as the magnet oscillates -

Consider the loss of energy due to various factors.

- G shows no deflection.
- G shows deflection to the left and right, but the amplitude steadily decreases.
- G shows deflection to the left and right with constant amplitude.
- G shows deflection on one side only.

**Q.**A lamp consumes only 50% of peak power in an a.c. circuit. What is the phase difference between the applied voltage and the circuit current

- π6
- π4
- π2
- π3

**Q.**Two identical conductors P and Q are placed on two frictionless, flat, conducting rails R and S, in a uniform magnetic field directed into the plane. If conductor P is moved in the direction shown in the figure with a constant speed, then the conductor Q -

- will be attracted towards conductor P
- will be repelled away from conductor P
- will remain stationary
- first attracted and then repelled away from conductor P

**Q.**In a circuit containing an inductance of zero resistance, the e.m.f. of the applied ac voltage leads the current by

- 90∘
- 30∘
- 0∘
- 45∘

**Q.**Average power in an A.C circuit is 50 watt. Resistance of circuit is 32 Ω, and source voltage is 50V. Power factor of this circuit is

- 0.8
- 0.6
- 35
- 34

**Q.**

The average power dissipation in pure capacitive circuit is:

zero

**Q.**25πμ F capacitor and 3000-ohm resistance are joined in series to an ac source of 200 volt and 50 sec−1 frequency.The power factor of the circuit and the power dissipated in it will respectively

- 4.8, 0.6 W
- 0.06, 0.6 W
- 0.6, 4.8 W
- 0.6, 0.06 W

**Q.**ntThe phase difference between current and voltage, when the freqeuency of applied emf is w + R/2L (w is resonance frequency) in a series LCR circuit isn nt(a) pi/2 (b) pi/4 (c)pi/6 (d)0n

**Q.**Find the energy stored in the circuit containing four capacitors at the steady state.

- 99 μJ
- 49.5 μJ
- 62 μJ
- 75 μJ

**Q.**47. In an AC circuit , maximum value of voltage is 423 volts. Its effective voltage?

**Q.**For an RLC circuit driven with voltage of amplitude vm and frequency ω0=1√LC, the current exhibits resonance. The quality factor, Q, is given by

- R(ω0C)
- CRω0
- ω0LR
- ω0RL

**Q.**A parallel plate capacitor is filled by a dielectric whose relative permittivity varies with the applied voltage (U) as ϵ=α U where α=2V−1. A similar capacitor with no dielectric is charged to U0=78V. It is then connected to the uncharged capacitor with the dielectric. Find the final voltage on the capacitors.

**Q.**

Two equal resistance are connected in the gaps of a metre bridge if the resistance in the left is increased by 10% the balancing point shifts

1.10% to right

2.10% to left

3.9.6%to right

4.4.8% to right

**Q.**In a chamber, a uniform magnetic field of 6.5G(1G=10−4 T) is maintained. An electron is shot into the field with a speed of 4.8×106 ~m/s normal to the field. Obtain the frequency of revolution of the electron in its circular orbit. Does the answer depend on the speed of the electron? Explain

Take (e=1.6×10−19C, mθ=9.1×10−31 kg).