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Recent questions and answers in Alternating current

Questions >> CBSE XII >> Physics >> Alternating current

A coil has an inductance of $5\;H$ and resistance $20\; \Omega$ . An emf of $100\; v$ is applied to it. What is the energy stored in the magnetic field, when the current has reached its final value .

answered Sep 28, 2016 by meena.p

1 answer

What is the peak value of $220\;v\;a.c$

answered Sep 28, 2016 by meena.p

1 answer

In a series LCR circuit , the voltage across an inductor, a capacitor and a resistor are $30\;v, 30\;v$ and $60\;v$ respectively . What is the phase difference between the applied voltage and the current in the circuit .

answered Sep 28, 2016 by meena.p

1 answer

In an a.c circuit , there is no power consumption in an ideal inductor . why ?

answered Sep 28, 2016 by meena.p

1 answer

A resistor of resistance $100 \Omega$ is connected to an ac source. $E= (12 v) \sin (250 \pi s^{-1})t$ Find the energy dissipated as heat during $t=0$ to $t= 1.0\;ms$

answered Sep 28, 2016 by meena.p

1 answer

An electric motor operation on a $50\;v$ d.c supply draws a current of $12\;A$ . If the efficiency of the motor is $30\%$ , estimate the resistance of the motor .

answered Sep 28, 2016 by meena.p

1 answer

A generator develops am e.m.f of $120\;v$ and has a terminal potential difference of $115\;v$ when the as mature current is $25\;A$ What is the resistance of the as mature ?

answered Sep 28, 2016 by meena.p

1 answer

Can a capacitor be used instead of a choke coil in controlling a.c ?

answered Sep 28, 2016 by meena.p

1 answer

Why do we prefer a choke coil to a rheostat in controlling a.c ?

answered Sep 27, 2016 by meena.p

1 answer

Why are air cored chokes used for reduced high frequency a.c ?

answered Sep 27, 2016 by meena.p

1 answer

The calculate the current drawn by the prime of a transformer which steps down $200\;v$ to $20\;v$ to operate a device of resistance $20 \Omega$ the efficiency of the transformer to be $80\%$

answered Sep 27, 2016 by meena.p

1 answer

A transformer has an efficiency of $80\%$ and works at 100 volt and 4 kw. If the secondary voltage is $240\;volt$ calculate the primary and secondary currents

answered Sep 27, 2016 by meena.p

1 answer

A transformer has 50 turns in the primary and 100 in the secondary . If the primary is connected to a $220\;v$ d.c supply . What will be the voltage across the secondary ?

answered Sep 27, 2016 by meena.p

1 answer

A 20 V , 750 Hz source is connected to a series combination of $R= 100\; \Omega, C= 10 \mu F $ and $L= 0.1803\;H$ . Calculate the time in which resistance will get heated by $10^{\circ}$ if thermal capacity of the material $=25 \%$

answered Sep 27, 2016 by meena.p

1 answer

Two different coils have self inductance $L_1=8\;mH$ and $L_2=2\;mH$. At a certain instant , the current in the two coils is increasing at the same constant rate and the power supplied to the two coils is the same . Find the ratio of the current and energy stored.

answered Sep 27, 2016 by meena.p

1 answer

Two different coils have self inductance $L_1=8\;mH$ and $L_2=2\;mH$. At a certain instant , the current in the two coils is increasing at the same constant rate and the power supplied to the two coils is the same . Find the ratio of induced voltage at that instant

answered Sep 27, 2016 by meena.p

1 answer

1 Mw power is to be delivered from a power station to a town $10\;km$ away. One uses a pair of cer wires $0.5\;cm$ for this purpose . Calculate the fraction of ohmic losses to power transmitted if power is transmitted comment on the feasibility of doing this ?

answered Sep 27, 2016 by meena.p

1 answer

An electrical drive draws 2 kw power from AC mains [ Voltage $223 V(rms) = \sqrt {50,000}\;v$ ]. The current differs (lags) in phase by $\phi (\tan \phi = -\large\frac{-3}{4} )$ as compared to voltage . Find $I_{max}$ another device has twice the value of $R,X_c$ and $X_L$. How are the answers affected ?

answered Sep 27, 2016 by meena.p

1 answer

An electrical drive draws 2 kw power from AC mains [ Voltage $223 V(rms) = \sqrt {50,000}\;v$ ]. The current differs (lags) in phase by $\phi (\tan \phi = -\large\frac{-3}{4} )$ as compared to voltage . Find $ X_C - X_L$

answered Sep 26, 2016 by meena.p

1 answer

An electrical drive draws 2 kw power from AC mains [ Voltage $223 V(rms) = \sqrt {50,000}\;v$ ]. The current differs (lags) in phase by $\phi (\tan \phi = -\large\frac{-3}{4} )$ as compared to voltage . Find R

answered Sep 26, 2016 by meena.p

1 answer

Explain why the reactant offered by an inductor increased with increased frequency of an alternating voltage.

answered Sep 26, 2016 by meena.p

1 answer

Explain why the reactant provided by a capital to an alternating current decreases with increasing frequency .

answered Sep 26, 2016 by meena.p

1 answer

A $60\;w$ load is connected to the secondary of a transformer whose primary draws line voltage. If a current of $0.54\;A$ flows in the load, what is the current in the primary coil ? Comment on the type of transformer bring used ?

answered Sep 26, 2016 by meena.p

1 answer

A Coil of $0.01$ Henry inductance and 1 ohm resistance is connected to $200 \;volt,50 Hz,ac $ supply . Find the impedance of the circuit and time lag between max. alternating voltage and current .

answered Sep 26, 2016 by meena.p

1 answer

Both alternating current and direct current are measured in ampere. But how is the ampere defined defined for an alternating current .

answered Sep 26, 2016 by meena.p

1 answer

How does the sign of the phase angle $\phi$ , big which the supply voltage leads the current in an LCR series circuit , change as the supply frequency is gradually increased from very low to very high values ?

answered Sep 23, 2016 by meena.p

1 answer

Can the instantaneous power output of an ac source ever he negative ? can the average power output be negative ?

answered Sep 23, 2016 by meena.p

1 answer

In LC circuit , is considered analogous to a harmonically oscillating spring block system, which energy of LC circuit would be analogous to potential energy and which one analogous to kinetic energy ?

answered Sep 22, 2016 by meena.p

1 answer

The line that draws power supply to your house from street has

answered Sep 22, 2016 by meena.p

1 answer

For an LCR circuit , the power transferred forms the diving source to the drives oscillator is $P= I^2 z \cos \phi$

answered Sep 22, 2016 by meena.p

1 answer

Electrical energy is transmitted over large distance at high alternating voltage . Which of the following statement are correct ?

answered Sep 22, 2016 by meena.p

1 answer

In an alternating current circuit consisting of elements in series, the current increases on increasing the frequency of supply . Which of the following elements are likely to continue the circuit ?

answered Sep 22, 2016 by meena.p

1 answer

As the frequency of an ac circuit increase, the current first increase and then decrease . What combination of circuit elements is most likely to comprise the circuit ?

answered Sep 22, 2016 by meena.p

1 answer

The output of a step down transformer is measured to be $24\;v$ when connected to a 12 walt light bulb. The value of the peak current is

answered Sep 22, 2016 by meena.p

1 answer

An inductor of a reactance $1 \Omega$ and a resistor of $2 \Omega$ are connected in series to the terminals of a$6\;v(r.m.s)$ a.c source. The power dissipated in the circuit is

answered Sep 22, 2016 by meena.p

1 answer

Which of the following combination should be selected for better turning of an LCR circuit used for communication ?

answered Sep 22, 2016 by meena.p

1 answer

The voltmeter the resonant frequency in an L.C.R series circuit with a generator .

answered Sep 21, 2016 by meena.p

1 answer

When a voltage measuring device is connected to AC mains , the meter shows the steady input voltage opf $220\;v$ This means

answered Sep 21, 2016 by meena.p

1 answer

An alternating current generator has an internal resistance $R_g$ and an internal reluctance $X_g$.It is used to supply power to a passive loud consisting of a resistance $R_g$ and a reluctance $x_L$ . For maximum power to be delivered from the generator to the load, the value of $X_L$ is equal to

answered Sep 21, 2016 by meena.p

1 answer

If the rms current in a 50 Hz a.c circuit is $5\;A$ , the value of the current $ \large\frac{1}{300}$ seconds after its value becomes zero is

answered Sep 21, 2016 by meena.p

1 answer

A small town with a demand of $800\;kw$ of electric power at $220\;v$ is situated $15\;km$ away from an electric plant generating power at $440\;v$. The resistance of the two line wires carrying power is $0.5\;\Omega$ per km. The town gets power from the lines through a $40,000-220\;v$ Step down transformation. Neglect leaked losses . hence explain why high voltage transmission is preferred .

answered Sep 21, 2016 by meena.p

1 answer

A small town with a demand of $800\;kw$ of electric power at $220\;v$ is situated $15\;km$ away from an electric plant generating power at $440\;v$. The resistance of the two line wires carrying power is $0.5\;\Omega$ per km. The town gets power from the lines through a $4000-220\;v$ Step down transformation at a substation in the town .Characterize the step up transformer at the plant

answered Sep 21, 2016 by meena.p

1 answer

A small town with a demand of $800\;kw$ of electric power at $220\;v$ is situated $15\;km$ away from an electric plant generating power at $440\;v$. The resistance of the two line wires carrying power is $0.5\;\Omega$ per km. The town gets power from the lines through a $4000-220\;v$ Step down transformation at a substation in the town . How much power must the plant supply , assuming there is negligible power loss due to leakage ?

answered Sep 21, 2016 by meena.p

1 answer

A small town with a demand of $800\;kw$ of electric power at $220\;v$ is situated $15\;km$ away from an electric plant generating power at $440\;v$. The resistance of the two line wires carrying power is $0.5\;\Omega$ per km. The town gets power from the lines through a $4000-220\;v$ Step down transformation at a substation in the town . Estimate the power loss in the form of heat

answered Sep 21, 2016 by meena.p

1 answer

At a hydroelectric power plant , the water pressure head is at a height of 300 m and the water flow available is $100 m^3 s^{-1} $. If the turbine generator efficiency is $60\%$ estimate the electric power available from the plant $(g= 9.8 ms^{-2})$

answered Sep 20, 2016 by meena.p

1 answer

A power transmission line feeds input power at $2300\;v$ to a step down transformer , with its primary winding's having $4000$ turns. What should be the number of turns in the secondary windings in order to get out put power at $230\;v$

answered Sep 20, 2016 by meena.p

1 answer

Why is choke coil needed in the use of flourscent takes with a.c mains? Why can we not use an ordinary resistor instead of choke coil ?

answered Sep 20, 2016 by meena.p

1 answer

A check coil in series with a lamp is connected to a d.c line. The lamp is seen to shine brightly and insertion of an iron core in the choke causes no change in the lamps brightness. Predict the corresponding observation if the connection is to as a.c line

answered Sep 20, 2016 by meena.p

1 answer

An applied voltage signal consists of a super position of a d.c voltage and a.c voltage of high frequency . The circuit consists of an inductor and a capacitor in series. will the d.c signal will appear across c and the a.c signal will appear across L ? At high frequencies

answered Sep 20, 2016 by meena.p

1 answer

A capacitor is used in the primary circuit of an induction coil . Why ?

answered Sep 20, 2016 by meena.p

1 answer

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