Download Alternating Current

(Q.1) An alternating voltage (in volts) = 100
sin 100t is connected to one
microfarad capacitor. What will bethe reading of the ammeter?
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(Q.2) What doesa large value of Q imply in context with resonance?
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(Q.3) What is the dimension for
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?
(Q.4) What is the phase difference between the voltage drop across L and C in a
series LCR circuit connected to an a.c. source?
(Q.5)
(Q.6)
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(Q.8)
Peak value of emf of an a.c source is E0. What is its rms value ?
When a.c is fed to moving coil galvanometer, it shows no deflection. Why?
Is it possible to use capacitor instead of choke coil for reducing a.c.?
How is it possible to improve the quality factor of a series resonance
circuit?
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(Q.9) In a pure LC circuit, what is the energy stored when peak current is IO?
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(Q.10) What is the minimum value of power factor and when does it occur?
(Q.11) Using an AC voltmeter, the potential difference in the electrical line in a
house is read to be 230 Volt. If the line frequency is known to be 50 cycles
per second, What will be the equation of the line voltage?
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(Q.12) What Ratio of the mean value over half cycle to the r.m.s value of an AC?
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(Q.13) A capacitor of capacitance 1µF and a resistor of resistance 105
are
connected in series with a battery of emf 100 volt and negligible internal
resistance. What is the Time constant of the circuit?
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(Q.14) A coil of resistance 300
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and self inductance 1.5 henry is connected to an
a-c source of frequency 100/
between voltage and current?
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hertz. What is the phase difference
(Q.15) The power factor varies between:
(A) 0 to 0.5
(B) 0.5 to 1
(C) 0 to 1
(D) 1 and 2
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(Q.16) A 20 µF capacitor is connected across a 200V, 50 Hz ac supply. What isthe
peak current through the circuit ?
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(Q.17) A capacitor in an ideal LC circuit is fully charged by a DC source. Then it is
disconnected from DC source, then what is the current in the circuit?
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(Q.18) The tuning circuit of a radio receiver has a resistance of 50
, an inductor
of 10 mH and a variable capacitor. A 1 MHz radio wave produces a
potential difference of 0.1 mV. What will bethe value of the capacitance to
produceresonance? (Take
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):
(Q.19) What will be the Maximum power dissipated in an LCR circuit at
Resonance?
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(Q.20) An LC circuit has an inductance 2.81 mH and a capacitance of 9pF. The
capacitor is initially charged with a 12 V battery.What is the total energy
stored in the circuit?
(Q.21) The sum of the instantaneous current values over one complete cycle is
zero, and the average current is zero. What is the average power
consumed?
(Q.22) A 12 W resistor and a 0.21 henry inductor are connected in series to an a.c.
source operating at 20 volt, 50 cycle. What will be the phase angle
between the current and source voltage?
(Q.23) In an LR circuit, f = 50 Hz, L=2H, E=5 volts,
. What is theEnergy
stored in inductor?
(Q.24) The maximum current through a pure capacitor of capacitance C is I0. The
maximum emf is
. If the frequency is 50 Hz, What isthe average power
dissipated through the capacitor is?
(Q.25) What is the peak value of house hold line voltage?
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(Q.26) An instrument is rated 200 W, 484
for a 220 V supply. What is the peak
voltage and the rms current through the instrument?
(Q.27) In a transformer, the voltage is stepped up from 200 V to 500 V. If the
current in the primary coil was 5.0 A, then what will be the current in the
secondary?
(Q.28) Iron has been used as the core of the transformer to reduce the loss due
to:
(A) Flux leakage
(B) Hysteresis
(C) Eddy currents
(D) Resistance
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(Q.29) Through which of the ac circuit elements both the emf and current are in
the phase ?
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(Q.30) The current in an ac circuit is I = I0 sin
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and the emf is V = V0 cos
.
What isthe power dissipation in the circuit?
(Q.31) In an RCL circuit, capacitance is changed from C to 2C. For the resonant
frequency to remain unchanged, the inductance should be changed from L
to :
(A) 4 L
(B) 2L
(C) L/2
(D) L/4
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(Q.32) In an a.c. circuit V and I are given by
V = 100 sin (100 t) volts
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I = 100 sin (100 t +
/3) mA
What isthe power dissipated in the circuit?
(Q.33) In a circuit L, C and R are connected in series with an alternating voltage
source of frequency f. The current leads the voltage by 45°. What is the
value of C?
(Q.34) An instantaneous current from an a.c. Source is given by I=5 sin314t.
What is the rms value of the current?
(Q.35) What is the inductive reactance of a coil if current through it is 800 mA
and the voltage across it is 40 V?
(Q.36) Which of the following quantities remain constant in a step-down
transformer?
(A) Current
(B) Voltage
(C) Power
(D) None of these
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(Q.37) Justify the statement that “An inductor acts as a conductor for d.c”.
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(Q.38) Why is a capacitor always able to bypass a.c.?
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(Q.39) Why cannot we use a.c. for electrolysis purpose?
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(Q.40) How can we improve power factor of given circuit, by use of appropriate
capacitance in the circuit?
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(Q.41) In an a.c circuit, there is no power consumption in an ideal inductor.
Explain.
(Q.42) State why A.C. voltage preferred over D.C. voltage?
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(Q.43) If the voltage in an A.C. circuit is given by
a) Find peak and rms value of voltage.
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b) Frequency of A.C.
(Q.44) An A.C. source of voltage
is connected to a resistor of
resistance 20?‫ ٮ‬Find the rms value of the current through the resistor.
(Q.45) Obtain the resonant frequency and Q-factor of a series L-C-R circuit with L
= 3H, C = 27μF and R = 7.4?‫ټ‬/strong>
(Q.46) What can be said about power losses in a purely capacitive and inductive
circuits?
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(Q.47) A pure inductor of 25 mH is connected to a source of 220 V. Find the
inductive reactance and rms current in the circuit if the frequency of the
source is 50 Hz ?
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(Q.48) A capacitor, resistor and inductor of 40 mH are connected in series to an
a.c. source of frequency 60 Hz. Calculate the capacitance of the capacitor,
if current is in phase with the voltage.
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(Q.49) Show that the resonance of series LCR circuit driven by a.c. source is given
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by
?
(Q.50) An a.c. source of frequency 50 Hz is connected to a 50 mH inductor and a
bulb. The bulb glows with some brightness. Calculate the capacitance of
the capacitor to be connected in series with the circuit so that the bulb
glows with maximum brightness.
(Q.51) A 100 μF capacitor in series with a 50 §Ù resistance is connected to a 150
V, 30 Hz supply.
(a) What is the maximum current in the circuit?
(b) What is the phase difference between current and voltage?
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(Q.52) In any a.c. circuit , is the applied instantaneous voltage equal to the
algebraic sum of the instantaneous voltages across the series elements of
the circuit?Is the same true for rms voltage?
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(Q.53) Find the power consumed in a circuit having a resistance of 30 ohm in
series with an inductance of 40 ohm in series with an a.c. with peak
current of 1 ampere and peak voltage of 220 volt.
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(Q.54) A power transmission line feeds input power at 2200 Vto a step down
transformer with its primary windings having 2000 turns.What should be
the number of turns in the secondary in order to get output power 220
volt?
(Q.55) Definepower factor.What is the maximum and minimum value of power
factor of an a.c. circuit?
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(Q.56) The output voltage of an ideal transformer connected to a 240V a.c. mains
is 24V.If this transformer is used to light a bulb with rating 24V,
24W,calculate the current in the primary coil of the circuit.
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(Q.57) A 10 μF capacitor is charged to a 25 volt of potential.The battery is then
disconnected and pure 100 mH coil is connected across the capacitor so
that LC oscillations are set up.Calculate the maximum current in the coil.
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(Q.58) State the condition under which the phenomenon of resonance occurs in a
series L-C-R circuit.Plot a graph showing variation of current with
frequency of a.c. source in a series L-C-R circuit.
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(Q.59) A capacitor, a resistor and a 40 mH inductor are connected in series to an
a.c. source of frequency 60 hz.Calculate the capacitance of the capacitor, if
current is in phase with the voltage.
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(Q.60) A coil having aresistance of 7 ohm and an inductance of .6H is connected to
an AC source of 110 volts having frequency 20 Hz.Find the rms and peak
value of the current in the circuit.
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(Q.61) State the reasons for energy losses in transformers.
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(Q.62) What is meant by impedance? Using a phasor diagram or otherwise derive
the expression for the impedance of an a.c. circuit containing L, C and R in
series. Find the expression for resonant frequency.
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(Q.63) What is choke coil? Why is it preferred to resistance in a.c. circuit? If the frequency of emf is increased, then
what will be the effect on the
currents flowing through the circuits given below?
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(Q.64) An a.c. circuit containing 800 mH and a 60 μF capacitor is in series with 15 ohm resistance.They
are connected to 230 volt, 50 hz a.c. supply.Obtain the average power transferred to each
element and the total power absorbed.
(Q.65) An a.c. circuit having an inductor and a resistor in series draws a power of 560 Wfrom an a.c.
source marked 210 V,60hz.If the power factor of the circuit is 0.8 ,calculate
(a) the impedance of the circuit.
(b) the inductance of the inductor used.
(Q.66) A 100 mH inductor , a 25 μF capacitor and a 15 ohm resistor are connected in series to a 120
volt,50 hz a.c. source. Calculate the
(a) impedance of the circuit at resonance.
(b) current at resonance.
(c) resonant frequency.
(Q.67) When a series combination of inductance and resistance are connected with a 10V ,50 hz a.c.
source, a current of 1 A flows in the circuit.The voltage leads the current by a phase angle of
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.Calculate the value of resistance and inductance.