CBSE Questions for Class 12 Medical Physics Alternating Current Quiz 7 - MCQExams.com

State whether given statement is True or False
In order to get maximum power transfer from a capacitive source, the load must have an impedance that is the complex conjugate of the source impedance.
  • True
  • False

An oscillating circuit contains an inductor of inductance $$ { 10 }^{ -6 }$$ H and two capacitor each of capacitance $$5\times { 10 }^{ -6 }$$ farad connected in parallel. Then the resonance frequency of the circuit is
  • $$\dfrac { { 10 }^{ 5 } }{ 2\pi } $$
  • $$\dfrac { { 10 }^{ 5 } }{ \pi } $$
  • $$\dfrac { { 3\times 10 }^{ 5 } }{ 2\pi } $$
  • $$\dfrac { \sqrt { { 2\times 10 }^{ 5 } } }{ \pi } $$
A $$100\Omega$$ resistor is connected to a $$220V,50Hz$$ AC supply. Find rms value of current in the circuit and the net power consumed for a complete cycle.
  • $$2.20A,484W$$
  • $$3.20A,564W$$
  • $$1.60A,278W$$
  • $$5.80A,646W$$

When $$100\ volt\ DC$$ is applied across a solenoid, a current of $$1.0\ amp$$ flows in it. When $$100\ volt\ AC$$ is applied across the same coil, the current drops to $$0.5\ amp.$$ If the frequency of the AC source is $$50\ Hz$$ the impedance and inductance of the solenoid are:
  • $$200\ \Omega$$ and $$0.55\ H$$
  • $$100\ \Omega$$ and $$0.86\ H$$
  • $$200\ \Omega$$ and $$1.0\ H$$
  • $$100\ \Omega$$ and $$0.93\ H$$
In resonance, frequency of LC circuit is :
  • $$\dfrac { 1 }{ 2\pi } \sqrt { LC } $$
  • $$\dfrac { 1 }{ 2\pi LC } $$
  • $$\dfrac { 1 }{ 2\pi } \sqrt { \dfrac { L }{ C } } $$
  • $$\dfrac { 1 }{ 2\pi \sqrt { LC } } $$
In an LCR circuit the potential difference between the terminal of the inductance is $$60\ V$$, between the terminals of the capacitor is $$30\ V$$ and that between the terminals of the resistance is $$40\ V$$. The supply voltage will be equal to:
  • $$130\ V$$
  • $$10\ V$$
  • $$50\ V$$
  • $$70\ V$$

The peak value of an alternating e.m.f. E given by $$E={ E }_{ 0 } \cos\omega t$$ is 10 volt and frequency is 50 Hz. At time $$t = (1/600)$$ sec, the instantaneous value of e.m.f. is
  • $$10$$ volt
  • $$5\sqrt { 3 } $$ volt
  • $$5$$ volt
  • $$1$$ volt

A series LCR circuit is tuned to resonance. If the angular frequency of the applied AC voltage at resonance is $$\omega $$, the impedance of the circuit then is:
  • $$R+\omega L+(\frac { 1 }{ \omega C } )$$
  • R
  • $$\sqrt { { R }^{ 2 }+\omega L+{ \left( \frac { 1 }{ \omega C } \right) }^{ 2 } } $$
  • $$\sqrt { { R }^{ 2 }+{ \left( \omega L-\frac { 1 }{ \omega C } \right) }^{ 2 } } $$
A series $$LCR$$ circuit is connected to a source of alternating emf $$50 \ V$$ and if the potential differences across inductor and capacitor are $$90\  V$$ and $$60\  V$$ respectively, the potential difference across resistor is:
  • $$400\  V$$
  • $$40\  V$$
  • $$80\  V$$
  • $$1600\  V$$
In an LCR circuit, the capacitance is made one-fourth, when in resonance. Then what should be the change in inductance, so that the circuit remains in resonance?
  • 4 times
  • (1/4) times
  • 8 times
  • 2 times
A light bulb is rated at $$100W$$ for a $$220V$$ supply. Find the peak voltage of the source:
  • $$111V$$
  • $$211V$$
  • $$311V$$
  • $$411V$$
In R-L-C series circuit, the potential differences across each element is $$20V$$. Now the value of the resistance alone is doubled, then P.D. across R, L and C respectively.
  • $$20V, 10V, 10V$$
  • $$20V, 20V, 20V$$
  • $$20V, 40V, 40V$$
  • $$10V, 20V, 20V$$
A sine wave with an rms value of $$12 V$$ is riding on a dc level of $$18 V$$. The maximum value of the resulting waveform is
  • $$6 V$$
  • $$30 $$
  • $$35 V$$
  • $$0 V$$
For a certain load, the true power is $$150 W$$ and the reactive power is $$125 W$$. The apparent power is
  • $$19.52 W$$
  • $$195.2 W$$
  • $$275 W$$
  • $$25 W$$
A sinusoidal voltage $$V=200sin314t$$ is applied to a $$10\Omega$$ resistor. Find rms current.
  • $$14.14A$$
  • $$28.28A$$
  • $$56.56A$$
  • $$100A$$
 A sinusoidal voltage $$V=200sin314t$$ is applied to a $$10\Omega$$ resistor. Find rms voltage.
  • $$141.4V$$
  • $$314.2V$$
  • $$519.6V$$
  • $$278.9V$$
A sinusoidal voltage $$V=200sin314t$$ is applied to a $$10\Omega$$ resistor. Find the frequency of the supply.
  • $$40 Hz$$
  • $$50 Hz$$
  • $$60 Hz$$
  • $$80 Hz$$
A sinusoidal voltage $$V=200sin314t$$ is applied to a $$10\Omega$$ resistor. Find the peak voltage.
  • $$200V$$
  • $$400V$$
  • $$600V$$
  • $$800V$$
A $$100\Omega$$ resistor is connected to a $$220V, 50Hz$$ AC supply. Find $$rms$$ value of current in the circuit :
  • $$1.10A$$
  • $$2.20A$$
  • $$3.30A$$
  • $$4.40A$$
A light bulb is rated at $$100W$$ for a $$220V$$ supply. Find the rms current through the bulb:
  • $$0.25A$$
  • $$0.45A$$
  • $$0.65A$$
  • $$0.85A$$
A condenser of  $$250 \mu F$$ is connected in parallel to a coil of inductance  0.16 mH, while its effective resistance is $$20 \Omega$$. Determine the resonant frequency.
  • $$9\times 10^4 Hz$$
  • $$16\times 10^7 Hz$$
  • $$8\times 10^5 Hz$$
  • $$9\times 10^3 Hz$$
If a capacitance C is connected in series with an inductor of inductance L, then the angular frequency will be
  • $$\sqrt{\dfrac{1}{LC}}$$
  • $$\sqrt{\dfrac{L}{C}}$$
  • LC
  • $$\sqrt{LC}$$
In A.C. circuit in which inductance and capacitance are joined in series, current is found to be maximum when the value of inductance is $$0.5H$$ and the value of capacitance is $$8\mu F$$. The angular frequency of applied alternating voltage will be
  • 400 Hz
  • 500 Hz
  • 4000 Hz
  • 5000 Hz
The reactance of coil when used in an A.C. power supply ( 220volts, 50 cycles/sec) is 50ohms. The inductance of the coil is nearly
  • 0.16 H
  • 0.22 H
  • 2.2 H
  • 1.6 H
In a series RC circuit, when the frequency and the resistance are halved, the impedance
  • doubles
  • is halved
  • is reduced to one-fourth
  • cannot be determined without values
A waveform has a baseline of $$3 V$$, a duty cycle of $$20$$%, and an amplitude of $$8 V$$. The average voltage value is
  • $$4 V$$
  • $$4.6 V$$
  • $$1.6 V$$
  • $$11 V$$
A series combination of resistor ($$R$$) and capacitor ($$C$$) is connected to an A.C. source of angular frequency '$$\omega$$'. Keeping the voltage same, if the frequency is changed to $$\omega/3$$, the current becomes half of the original current. Then the ratio of the capacitive reactance and resistance at the former frequency is:
  • $$\sqrt{0.6}$$
  • $$\sqrt{3}$$
  • $$\sqrt{2}$$
  • $$\sqrt{6}$$
Which one of the following graphs in following figure represents variation of reactance $$'X_c'$$ of a capacitor with frequency 'f' of an ac supply?
In a series LCR circuit, resonance occurring at 105Hz. At that time, the potential difference across the 100 resistance is 40V while the potential difference across the pure inductor is 30v. The inductance L of the inductor is equal to
  • $$2.0 \times 10^{-4}$$
  • $$3.0 \times 10^{-4}$$
  • $$1.2 \times 10^{-4}$$
  • $$2.4 \times 10^{-4}$$
An inductor (L = 20 H), a resistor (R = 100 $$\Omega$$) and a battery (E = 10 V) are connected in series. After a long time, the circuit is short-circuited and then the battery is disconnected. Find the current in the circuit at 1 ms after short circuiting.
  • $$4.5 \times 10^5 A$$
  • $$3.2 \times 10^{-5} A$$
  • $$9.9\times 10^{-2} A$$
  • $$6.7 \times 10^{-4} A$$
If the value of C in a series RLC circuit is decreased, the resonant frequency
  • is not affected
  • increases
  • is reduced to zero
  • decreases
In a series RLC circuit that is operating above the resonant frequency, the current
  • lags the applied voltage
  • leads the applied voltage
  • is in phase with the applied voltage
  • is zero
A $$90 \Omega$$ resistor, a coil with $$30 \Omega$$ of reactance, and a capacitor with $$50 \Omega$$  of reactance are in series across a $$12 V$$ ac source. The current through the resistor is
  • $$9 mA$$
  • $$90 mA$$
  • $$13 mA$$
  • $$130 mA$$
A resistor of $$3 k \Omega$$, a $$0.05 \mu F$$ capacitor and a $$120 mH$$ coil are in series across a $$5 kHz, 20 V$$ ac source.What is the impedance, expressed in polar form?
  • $$636\Omega$$
  • $$3,769\Omega$$
  • $$433\Omega$$
  • $$4,337\Omega$$
A $$12 \Omega$$  resistor, a $$40 \mu F$$ capacitor, and an $$8 mH$$ coil are in series across an ac source. The resonant frequency is
  • $$28.1 Hz$$
  • $$281 Hz$$
  • $$2,810 Hz$$
  • $$10 Hz$$
A $$6 kHz$$ sinusoidal voltage is applied to a series RC circuit. The frequency of the voltage across the resistor is
  • $$0 Hz$$
  • $$12 kHz$$
  • $$6 kHz$$
  • $$18 kHz$$
A resistor and a capacitor are in series across a $$20 V$$ ac source. Circuit impedance is $$4.33 k \Omega$$. Current flow in the circuit is
  • $$9.2 mA$$
  • $$92 mA$$
  • $$4.6 mA$$
  • $$460 mA$$
In a parallel RC circuit, there is $$100 mA$$ through the resistive branch and $$100 mA$$ through the capacitive branch. The total rms current is
  • $$200 mA$$
  • $$100 mA$$
  • $$282 mA$$
  • $$141 mA$$
State whether given statement is True or False
In an ac circuit, power to the load peaks at the frequency at which the load impedance is the complex conjugate of the output impedance.
  • True
  • False
A resistor $$R$$, an inductor $$L$$ and capacitor $$C$$ are connected in series to an oscillator of frequency $$n$$. If the resonant frequency is $${ n }_{ r }$$, then the current lags behind voltage, when
  • $$n=0$$
  • $$n < { n }_{ r }$$
  • $$n={ n }_{ r }$$
  • $$n > { n }_{ r }$$
The natural frequency of the circuit shown in adjoining figure is
617734_7f62da4951874a0c9d74415b8f9567ff.png
  • $$\dfrac{1}{2\pi \sqrt{LC}}$$
  • $$\dfrac{1}{2\pi \sqrt{2LC}}$$
  • $$\dfrac{2}{2\pi \sqrt{LC}}$$
  • Zero
The rms value of a.c. voltage with peack of $$311 V$$ is
  • $$220 V$$
  • $$311 V$$
  • $$180 V$$
  • $$320 V$$
The average half-cycle value of a sine wave with a $$40 V$$ peak is
  • $$25.48 V$$
  • $$6.37 V$$
  • $$14.14 V$$
  • $$50.96 V$$
The instantaneous emf and current equations of an RLC series circuit are
$$e=200\sin { \left( \omega t-\dfrac { \pi  }{ 6 }  \right)  } $$
$$i=20\sin { \left( \omega t+\dfrac { \pi  }{ 6 }  \right)  } $$
The average power consumed per cycle is
  • Zero
  • $$2000 W$$
  • $$1000 W$$
  • $$500 W$$
An LC resonant circuit contains a capacitor $$400 pF$$ and an inductor $$100 \mu H$$. It is set into oscillations coupled to an antenna. Calculate the wavelength of the radiated electromagnetic wave.
  • $$377 \ mm$$
  • $$377 \ cm$$
  • $$377 \ m$$
  • $$3.77 \ cm$$
In the adjoining circuit, if the reading of voltmeter $$V_1$$ and $$V_2$$ are 300 volts each, then the reading voltmeter $$V_3$$ and ammeter A are respectively
617754_9cf210d13afd4fe1a684d8527cef3a68.png
  • 220 V, 2.2 A
  • 100 V, 2.0 A
  • 220 V, 2.0 A
  • 100 V, 2.2 A
An L-C-R circuit contains $$R=50\Omega $$, $$L=1 mH$$ and $$C=0.1\mu F$$. The impedence of the circuit will be minimum for a frequency of
  • $$\dfrac { { 10 }^{ 5 } }{ 2\pi } Hz$$
  • $$\dfrac { { 10 }^{ 6 } }{ 2\pi } Hz$$
  • $$2\pi \times { 10 }^{ 5 }Hz$$
  • $$2\pi \times { 10 }^{ 6 }Hz$$
The instantaneous values of current and voltage in an AC circuit are $$i=100\sin 314 t$$ amp and $$e=200\sin (314t+\dfrac{\pi}{3})V$$ respectively. If the resistance is $$1\Omega$$, then the reactance of the circuit will be:
  • $$\sqrt{3}\Omega$$
  • $$100\sqrt{3}\Omega$$
  • $$-200\sqrt{3}\Omega$$
  • $$-200/ \sqrt{3}\Omega$$
The value of alternating emf $$E$$ in the given circuit will be
638574_80ea10c2dc154a6f942c8ab190379b88.png
  • $$220 V$$
  • $$140 V$$
  • $$100 V$$
  • $$20 V$$
If L-R circuit connected to a battery of constant emf $$E$$ switch $$S$$ is closed at time $$t=0$$. If $$e$$ denotes the induced emf across inductor and $$I$$ the current in the circuit at any time $$t$$. Then which of the following graphs shows the variation of $$e$$ with $$I$$?
0:0:1


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