CBSE Questions for Class 12 Medical Physics Alternating Current Quiz 3 - MCQExams.com

Symbol of Inductance in electric circuit is-
The peak voltage of an AC supply is $$300V$$. What is the rms voltage?
  • $$121.2V$$
  • $$212.1V$$
  • $$343.4V$$
  • $$434.3V$$
A light bulb is rated at $$100W$$ for a $$220V$$ supply. Find the resistance of the bulb:
  • $$184\Omega$$
  • $$284\Omega$$
  • $$384\Omega$$
  • $$484\Omega$$
The rms value of current in an AC circuit is $$10A$$. What is the peak current?
  • $$14.1A$$
  • $$35.2A$$
  • $$58.9A$$
  • $$23.5A$$
In series LCR circuit, the capacitance is changed from $$C$$ to $$2C$$. The inductance should be changed from $$L$$ to ______ to obtain same resonance frequency.
  • $$4L$$
  • $${L}/{2}$$
  • $${L}/{4}$$
  • $$2L$$
The reactance of inductance at $$10^{4}Hz$$ is $$10^{4}\Omega$$. Its reactance at $$2\times 10^{4}Hz$$ will be :
  • $$10^{4}\Omega$$
  • $$2\times 10^{4}\Omega$$
  • $$3\times 10^{4}\Omega$$
  • $$4\times 10^{4}\Omega$$
If we increase the driving frequency in a circuit with a  purely resistive load, then amplitude $$V_R$$
  • remain in the same
  • increase
  • decrease
  • none
In a $$LC$$ circuit. Angular frequency at resonance is $$w$$. What will be the new angular frequency when inductor's introduces is made $$2$$ times and capacitance is made $$4$$ times?
  • $$\dfrac{w}{\sqrt{2}}$$
  • $$\dfrac{w}{2\sqrt{2}}$$
  • $$2w$$
  • $$\dfrac{2w}{\sqrt{2}}$$
The current which does not contribute to the power consumed in an AC circuit is called:
  • Non-ideal current
  • Wattless current
  • Convectional current
  • Inductance current
The power loss is less in transmission lines, when :
  • Voltage is less but current is more
  • Both voltage and current are more
  • Voltage is more but current is less
  • Both voltage and current are less
State whether given statement is True or False
In an RC circuit, the impedance is determined by both the resistance and the capacitive reactance combined.
  • True
  • False
When the frequency of the source voltage decreases, the impedance of a parallel RC circuit
  • increases
  • decreases
  • does not change
  • decreases to zero
In $$L-C-R$$ series circuit, the capacitor is changed from $$C$$ to $$4C$$. For the same resonant frequency, the inductance should be changed from $$L$$ to.
  • $$2L$$
  • $$\dfrac {L}{2}$$
  • $$\dfrac {L}{4}$$
  • $$4L$$
State whether True or False :
The impedance of a series RC circuit varies directly with frequency.
  • True
  • False
When the frequency of the AC voltage applied to series LCR circuit is gradually increased from a low value, the impedance of the circuit:
  • monotonically increases.
  • first increases and then decreases.
  • first decreases and then increases.
  • monotonically decreases.
If A.C. voltage is applied to a pure capacitor, then voltage across the capacitor _________.
  • Leads the current by phase angle $$\left(\displaystyle\frac{\pi}{2}\right)$$ rad.
  • Leads the current by phase angle $$(\pi)$$ rad.
  • Lags behind the current by phase angle $$\left(\displaystyle\frac{\pi}{2}\right)$$ rad.
  • Lags behind the current by phase angle $$(\pi)$$ rad.
State whether given statement is True or False
In a series RLC circuit, the larger reactance determines the net reactance of the circuit.
  • True
  • False
Power dissipated in pure inductance will be
  • $$\dfrac {LI^{2}}{2}$$
  • $$2LI^{2}$$
  • $$\dfrac {LI^{2}}{4}$$
  • Zero
When the frequency of AC is doubled, the impedance of an LCR series circuit:
  • is halved
  • is doubled
  • increases
  • decreases
If $$V=100 \sin 100t$$ volt, and $$I=100 \sin(100t+\dfrac {\pi}{6})A$$. then find the watt less power in watt?
  • $$10^{4}$$
  • $$10^{3}$$
  • $$10^{2}$$
  • $$2.5 \times 10^{3}{\sqrt{3}}$$
In AC circuit having only capacitor, the current _____.
  • Leads the voltage by $$\dfrac {\pi}{2}$$ in phase
  • Lags behind the voltage by $$\dfrac {\pi}{2}$$ in phase
  • Leads the voltage by $$\pi$$ in phase
  • Lags behind the voltage by $$\pi$$ in phase
'Z' is not.
  • Atomic number
  • Impedance
  • Zeta potential
  • Partition function
In a pure capacitive circuit if the frequency of ac source is doubled, then its capacitive reactance will be
  • remains same
  • doubled
  • halved
  • zero
In a series $$LCR\, AC$$ circuit, the current is maximum when the impedance is equal to:
  • the reactance
  • the resistance
  • zero
  • twice the reactance
  • twice the resistance
Statement A: With an increase in the frequency of AC supply inductive reactance increases.
Statement B: With an increase in the frequency of AC supply capacitive reactance increase.
  • A is true but B is false
  • Both A and B are true
  • A is false but B is true
  • Both A and B are false
In series L-C-R resonant circuit, to increase the resonant frequency :
  • L will have to be increased
  • C will have to be increased
  • LC will have to be decreased
  • LC will have to be increased
At low frequency a condenser offers :
  • high impedance
  • low impedance
  • zero impedance
  • impedance of condenser is independent of frequency
If in a series L-C-R ac circuit, the voltages across R, L, C are $$V_{1},V_{2},V_{3}$$ respectively. Then the voltage of applied AC source is always equal to :
  • $$V_{1}+V_{2}+V_{3}$$
  • $$\sqrt{V_{1}^{2}+(V_{2}+V_{3})^{2}}$$
  • $$V_{1}-V_{2}-V_{3}$$
  • $$\sqrt{V_{1}^{2}+(V_{2}-V_{3})^{2}}$$
If the frequency of an alternating e.m.f. is f in L-C-R circuit, then the value of impedance Z $$\underline{\hspace{0.5in}}$$ as log(frequency) increases :
  • increases
  • increases and then becomes equal to resistance, then it will start decreasing
  • decreases and when it becomes minimum, equal to the resistance then it will start increasing
  • go on decreasing
An inductance and resistance are connected in series with an A.C circuit. In this circuit
  • the current and P.d. across the resistance lead P.d across the inductance by $$\dfrac{\pi }{2}$$
  • the current and P.d across the resistance lags behind the P.d. across the inductance by angle $$\dfrac{\pi }{2}$$
  • The current across resistance leads and the P.d across resistance lags behind the P.d across the inductance by $$\dfrac{\pi }{2}$$
  • the current across resistance lags behind and the P.d across the resistance leads the P.d across the inductance by $$\dfrac{\pi }{2}$$
If a capacitor is connected to two different A.C. generators, then the value of capacitive reactance is:
  • directly proportional to frequency
  • inversely proportional to frequency
  • independent of frequency
  • inversely proportional to the square of frequency
A capacitor is connected to an A.C. circuit, then the phase difference between current and the voltage is :
  • $$\pi $$
  • $$\dfrac{\pi }{2}$$
  • $$\dfrac{-\pi }{2}$$
  • Zero
Ratio of impedance to capacitive reactance has
  • no units
  • ohm
  • ampere
  • tesla
Statement ( A ) : The reactance offered by an inductance in A.C. circuit decreases with the increase of AC frequency.
Statement ( B ) : The reactance offered by a capacitor in AC circuit increases with the increase of AC frequency.
  • A is true but B is false
  • Both A and B are true
  • A is false but B is true
  • Both A and B are false
A mixer of 100$$\Omega $$ resistance is connected to an A.C. source of 200V and 50 cycles/sec. The value of average potential difference across the mixer will be:
  • 308 V
  • 264 V
  • 220 V
  • zero
Choose the wrong statement of the following :
  • The peak voltage across the inductor can be less than the peak voltage of the source in an LCR circuit
  • In a circuit containing and a capacitor and an ac source the current is zero at the instant source voltage is maximum
  • When an AC source is connected to a capacitor, then the rms current in the circuit gets increased if a dielectric slab is inserted into the capacitor
  • In a pure inductive circuit emf will be in phase with the current
The instantaneous value of emf and current in an
A.C. circuit are; $$E=1.414sin\left ( 100\pi t-\frac{\pi }{4} \right )$$ ,
$$I=0.707sin(100\pi t)$$ . The current,
  • leads the voltage by $$45^{0}$$
  • lags behind the voltage by $$45^{0}$$
  • leads the voltage by $$90^{0}$$
  • lags behind the voltage by $$90^{0}$$
The equation of an alternating voltage is E=220E=220 .Then the impedance of the circuit is:
  • 10 ohm
  • 22 ohm
  • 11 ohm
  • 17 ohm
An inductor has a resistance $$R$$ and inductance $$L$$. It is connected to an AC source of emf $$E_{v}$$ and angular frequency $$\omega$$; then the current $$I_{v}$$ in the circuit is :
  • $$\dfrac{E_{v}}{\omega L}$$
  • $$\dfrac{E_{v}}{R}$$
  • $$\dfrac{E_{v}}{\sqrt{R^{2}+\omega ^{2}L^{2}}}$$
  • $$\sqrt{\left ( \dfrac{E_{v}}{R} \right )^{2}+\left ( \dfrac{E_{v}}{\omega L} \right )^{2}}$$
A pure inductor of self inductance 1 H is connected across an alternating voltage of 115 V and frequency 60 Hz. The reactance $$X_{L}$$ and peak current respectively are
  • 37.1$$\Omega $$, 0.43 A
  • 337.1$$\Omega $$, 0.43 A
  • 377.1$$\Omega $$, 0.43 A
  • 3.7$$\Omega $$, 0.42 A
The phase difference between alternating emf and current in a purely capacitive circuit will be
  • zero
  • $$\pi $$
  • $$-\dfrac{\pi }{2}$$
  • $$\dfrac{\pi }{2}$$
Assertion : In series LCR circuit, the resonance occurs at one frequency only.
Reason  : At resonance the inductive reactance is equal and opposite to the capacitive reactance.
  • A,R are true and R is the correct reason for A
  • A,R are true and R is not the correct reason for A
  • A is true, R is false
  • A is false, R is true
Voltage and current in an ac circuit are given by $$V = 5\sin \left (100\pi t - \dfrac {\pi}{6}\right )$$ and $$I = 4\sin \left (100 \pi t + \dfrac {\pi}{6}\right )$$.
  • Voltage leads the current by $$30^{\circ}$$
  • Current leads the voltage by $$60^{\circ}$$
  • Voltage leads the current by $$60^{\circ}$$
  • Current and voltage are in phase
The capacitor offers zero resistance to
  • D.C. only
  • A.C. & D.C.
  • A.C. only
  • neither A.C. nor D.C.
A coil of self - inductance $$\left ( \dfrac{1}{\pi } \right )$$H is connected in series with a 300$$\Omega $$ resistance. A voltage of 200V at frequency 200Hz is applied to this combination. The phase difference between the voltage and the current will be
  • $$tan^{-1}\left ( \dfrac{4}{3} \right )$$
  • $$tan^{-1}\left ( \dfrac{3}{4} \right )$$
  • $$tan^{-1}\left ( \dfrac{1}{4} \right )$$
  • $$tan^{-1}\left ( \dfrac{5}{4} \right )$$
In an A.C. circuit, containing an inductance and a capacitor in series, the current is found to be maximum when the value of the inductance is 0.5 Henry and capacitance is 8$$\mu $$F . The angular frequency of the input A.C. voltage must be equal to
  • 500 rad/sec
  • 4000 rad/sec
  • $$5 \times10^{5}$$ rad/sec
  • 5000 rad/sec
The frequency at which the inductive reactance of $$2\ H$$ inductance will be equal to the capacitive reactance of 2 $$\mu$$F capacitance (nearly)
  • 80 Hz
  • 40 Hz
  • 60 Hz
  • 20 Hz
In an LCR series circuit, the capacitor is changed from C to 4C. For the same resonant frequency, the inductance should be changed from L to
  • 2L
  • L/2
  • L/4
  • 4L
In an A.C circuit, a resistance R is connected in series with an inductance L. If the phase angle between voltage and current be $$45^{0}$$, the value of inductive reactance will be
  • $$\dfrac{R}{4}$$
  • $$\dfrac{R}{2}$$
  • $$R$$
  • $$\dfrac{R}{3}$$
When the frequency of applied emf in an LCR series circuit is less than the resonant frequency,then the nature of the circuit will be:
a) Capacitive     b) resistive      c) inductive
  • only a is true
  • only a and b are true
  • only b and c are true
  • a, b and c are true
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