Alternating current practice · Mixed difficulty

The voltage of an AC source varies with time according to the relation $E = 200\sin \left( {100\pi t} \right)\cos \left( {100\pi t} \right)$ Select correct statement.

Statement (A): An electric lamp is connected in series with a long solenoid of copper with air core and then connected to AC source. If an iron rod is inserted in solenoid the lamp will become dim.

Statement (B): If iron rod is inserted in solenoid, the induction of solenoid increases.

Alternating current cannot be measured by DC ammeter because

An alternating e.m.f. of angular frequency ω is applied across an inductance. The instantaneous power developed in the circuit has an angular frequency

If the capacity of a condenser is 1 F, then its resistance in a DC circuit will be

The power factor of good choke coil is

Write the equation of a sinusoidal voltage of rms valus $220 \mathrm{~V}$ and frequency $50 \mathrm{~Hz}$

An inductor of inductance L and resistor of resistance R are joined in series and connected by a source of frequency ω. Power dissipated in the circuit is

At high frequency, the capacitor offer

Hot wire ammeters can be used for measuring:

For an R-L-C circuit driven with voltage of amplitude ${v_m}$ and frequency ${\omega _0} = \frac{1}{{\sqrt {LC} }},$ the current exhibits resonance. The quality factor, Q is given by

A series LCR circuit is subjected to an AC signal of $200 \mathrm{~V}, 50 \mathrm{~Hz}.$ If the voltage across the inductor $(\mathrm{L}=10 \mathrm{~mH})$ is $31.4 \mathrm{~V},$ then the current in this circuit is

Assertion (A): An inductance and a resistance are connected in series with an AC circuit. In this circuit, the current and the potential difference across the resistance logs behind potential difference across the inductance by an angle $\frac{\pi}{2}.$
Reason (R): In L - R circuit, voltage leads the current by phase angle which depends on the value of inductance and resistance both.

The impedance of a circuit, when a resistance R and an inductor of inductance L are connected in series in an AC circuit of frequency $f$, is

An LCR series circuit with R=100Ω is connected to a 200 V,50 Hz a.c. source when only the capacitance is removed, the current leads the voltage by 60°. When only the inductance is removed, the current leads the voltage by 60°. The current in the circuit is

A capacitor becomes a perfect insulator for

An ac source of angular frequency ω is fed across a resistor r and a capctior C in series. The current registered is $I$. If the frequency of source is changed to ω/3 (maintaining the same voltage), the current in the circuit is found to be halved. Calculate the ratio of reactance to resistance at the original frequency ω

In order to obtain a time constant of 10 s in a R-C circuit containing a resistance of ${10^3}\mathrm{\Omega }$ , the capacity of the condenser should be

A transformer is used to light 140 W, 24 V lamp from 240 V AC mains. The current in the mains is 0.7 A. The efficiency of transformer is nearest to

In an ac circuit with voltage V and current I, the power dissipated is

Voltage and current in an ac circuit are given by $V=5 \sin \left(100 \pi t-\frac{\pi}{6}\right)$ and $I=4 \sin \left(100 \pi t+\frac{\pi}{6}\right)$

Transformer works on the principle of

Core of transformer is made up of

Mark the correct statement.

For a series R-L-C circuit:

(a) Voltage across L and C differ by $\pi$ phase

(b) Current through L and R are in same phase

(c) Voltage across R and L differ by $\pi/2$ phase

(d) Voltage across L and current through C differ by $\pi/2$ phase

A coil of resistance R and inductance L is connected to a battery of emf E volt. The final current in the coil is

What is the value of inductance L for which the current is a maximum in a series L-C-R circuit with $C = 10\mu \mathrm{F}$ and $\omega = 1000\;{\mathrm{s}^{ - 1}}?$

AC voltage V(t) $= \mathrm{20 sin}\,\mathrm{\omega t}$ of frequency 50 Hz is applied to a parallel plate capacitor. The separation between the plates is 2 mm and the area is $1\,{m^2}.$ The amplitude of the oscillating displacement current for the applied AC voltage is ….
[Take, ${\varepsilon _0} = 8.85 \times {10^{ - 12}}F/m]$

The primary coil of an ideal transformer has 100 turns and secondary coil has 200 turns. Then select the correct option.

A capacitor 50μF is connected to a supply of 220 V and angular frequency 50 rad ${\mathrm{s}^{ - 1}}$. The value of rms current in the circuit is