CBSE Questions for Class 12 Medical Physics Alternating Current Quiz 5 - MCQExams.com

An amplitude modulated (AM) radio operates at $$550 kHz$$ to $$1650 kHz$$. If $$L$$ is fixed and $$C$$ is varied for tuning then minimum and maximum value of $$C$$ is
  • C, 3C
  • C, 6C
  • C, 9C
  • C, 12C
The correct curve representing the variation of capacity reactance $$X_c$$ with frequency $$f$$ is
A resistance $$R$$ and a capacitor $$C$$ are joined to a source of $$AC$$ of constant e.m.f and variable frequency. The potential difference across $$C$$ is $$V$$. If the frequency of $$AC$$ is gradually increased, $$V$$ will
146787.png
  • increase
  • decrease
  • remain constant
  • first increase and then decrease
A series $$AC$$ circuit has a resistance of $$4 \Omega$$ and a reactance of $$3 \Omega$$. The impedance of the circuit is
  • $$5 \Omega$$
  • $$7 \Omega$$
  • $$12/7 \Omega$$
  • $$7/12 \Omega$$
The natural frequency of a $$L-C$$ circuit is
  • $$\displaystyle \frac{1}{2\pi \sqrt{LC}}$$
  • $$\displaystyle \frac{1}{2\pi} \sqrt{\frac{C}{L}}$$
  • $$\displaystyle \frac{1}{2\pi} \sqrt{\frac{L}{C}}$$
  • $$\displaystyle \sqrt{LC}$$
An $$AC$$ source producing emf $$\displaystyle E = E_0 [cos (100 \pi s^{-1}) t] + E_0  cos  [(500 \pi s^{-1})t ]$$ is connected in series with a capacitor and a resistance, the steady state current in the circuit is found to be $$i = i_1 [cos (100 \pi s^{-1}) t + \varphi_1] + i_2  cos  [(500 \pi s^{-1})t + \varphi_2]$$
  • $$\displaystyle i_1>i_2$$
  • $$\displaystyle i_1 = i_2$$
  • $$\displaystyle i_1 < i_2$$
  • Insufficient information
Which of the following plots may represent the reactance of a series $$LC$$ combination?
146700_757d6b928edf4635b95c48624b265779.png
  • (a)
  • (b)
  • (c)
  • (d)
In the adjacent circuit diagram, initially switch S is opened and the circuit is in steady state. At time $$t=0$$, the switch S is closed and the new steady state is reached. Choose the correct option (s)
1109230_f44695683154456fa10ef2b638a5142a.png
  • Current in the inductor when the circuit reaches the new steady state is 4A.
  • The net change in the magnetic flux in the inductor is 1.5 Wb
  • The potential difference across the inductor is 9 volt when the circuit reaches the new steady state
  • The change stored in the capacitor in the new steady state is 1.2 mC
An inductor, a resistor and a capacitor are joined in series with an $$AC$$ source. As the frequency of the source is slightly increased from a very low value, the reactance
  • of the inductor increases
  • of the resistor increases
  • of the capacitor increases
  • of the circuit increases
In an $$L-C-R$$ circuit the value of $$X_L,X_C$$ and $$R$$ are 300 $$\Omega$$, 200 $$\Omega$$ and 100 $$\Omega$$ respectively.The total impedance of the circuit will be
  • 600 $$\Omega$$
  • 200 $$\Omega$$
  • 141 $$\Omega$$
  • 310 $$\Omega$$
The resultant reactance in an $$L-C-R$$ circuit is
  • $$\displaystyle X_L+X_C$$
  • $$\displaystyle X_L-X_C$$
  • $$\displaystyle \sqrt{X^2_L+X^2_C}$$
  • $$\displaystyle \sqrt{X^2_L-X^2_C}$$
The angular frequency of an AC source is 10 radian/sec. The reactance of $$1 \mu F$$ capacitor will be
  • $$\displaystyle 10^4 \Omega$$
  • $$\displaystyle 10^2 \Omega$$
  • $$\displaystyle 10^1 \Omega$$
  • $$\displaystyle 10^5 \Omega$$
A solenoid of length 10 cm, diameter 1 cm, number of turns 500 with relative permeability of the core 2000, is connected to an ac source of frequency 50 Hz. Then, the reactance is
  • zero
  • 55 $$\Omega$$
  • 105 $$\Omega$$
  • 155 $$\Omega$$
An inductance coil of $$1$$ $$H$$ and a condenser of capacity $$1$$ $$pF$$ produce resonance. The resonant frequency will be
  • $$\displaystyle \dfrac{10^6}{\pi} Hz$$
  • $$\displaystyle 27 \pi \times 10^6 Hz$$
  • $$\displaystyle \dfrac{2\pi}{10^6} Hz$$
  • $$\displaystyle \dfrac{10^6}{2\pi} Hz$$
If the values of $$L, C$$ and $$R$$ in a series $$L-C-R$$ circuit are 10 mH, 100 $$\mu F$$ and $$100 \Omega$$ respectively then the value of resonant frequency will be
  • $$\displaystyle \frac{10^3}{2 \pi} Hz$$
  • $$\displaystyle 2\times 10^3 Hz$$
  • $$\displaystyle 2\times \frac{10^3}{pi}Hz$$
  • $$\displaystyle 10^3 Hz$$
An $$AC$$ voltmeter in an $$L-C-R$$ circuit reads 30 volt across resistance, 80 volt across inductance and 40 volt across capacitance. The value of applied voltage will be
  • 50 Volt
  • 25 Volt
  • 150 Volt
  • 70 Volt
A coil of 10 mH and 10 $$\Omega$$ resistance is connected in parallel to a capacitance of $$0.1 \mu F$$. The impedance of the
  • $$\displaystyle 10^2 \Omega$$
  • $$\displaystyle 10^4 \Omega$$
  • $$\displaystyle 10^6 \Omega$$
  • $$\displaystyle 10^8 \Omega$$
The reactance of a condenser of capacity 50 $$\mu$$F for an $$AC$$ of frequency $$2 \times 10^3$$ Hertz will be
  • 5 ohm
  • $$\displaystyle \frac{2}{\pi}$$
  • $$\displaystyle \frac{3}{\pi}$$
  • $$\displaystyle \frac{5}{\pi}$$
In the following circuit the values of $$L,C,R$$ and $$E_0$$ are 0.01 H, $$\displaystyle 10^{-5} F, 25 \Omega$$ and 220 volt respectively. The value of current flowing in the circuit at $$f=0$$ and $$f=\infty$$ will respectively be
147460.jpg
  • 8 $$A$$ and 0 $$A$$
  • 0 $$A$$ and 0 $$A$$
  • 8 $$A$$ and 8 $$A$$
  • 0 $$A$$ and 8 $$A$$
The capacitive reactance of a condenser of capacity 25$$\mu$$F for an AC of frequency 4000 Hz will be
  • $$\displaystyle \frac{5}{\pi} \Omega$$
  • $$\displaystyle \frac{10}{\pi} \Omega$$
  • $$\displaystyle 5 \pi \Omega$$
  • $$\displaystyle \frac{\pi}{5} \Omega$$
In the figure two identical bulbs, each with filament resistance $$100\ \Omega$$ are connected to a resistor $$R = 100\ \Omega$$, and an inductor $$\displaystyle (X_L = 100 \Omega)$$ as shown in the Figure. Then, which bulb glows more
148278.jpg
  • $$\displaystyle B_1$$
  • $$\displaystyle B_2$$
  • both glow equally
  • cannot be predicted
The values of $$X_L, X_C$$ and $$R$$ in an AC circuit are 8 $$\Omega$$, 6$$\Omega$$ and 10 $$\Omega$$ respectively. The total impedance of the circuit
  • $$\displaystyle 10.2 \Omega$$
  • $$\displaystyle 12.2 \Omega$$
  • $$\displaystyle 10 \Omega$$
  • $$\displaystyle 24.4 \Omega$$
The turning circuit of a radio receiver has a resistance of $$50\ \Omega$$, an inductor of $$10\ \text{mH}$$ and a variable capacitor. A $$1\ \text{MHz}$$ radio wave produces a potential difference of $$0.1\ \text{mV}$$. The values of the capacitor to produce resonance is (Take $${\pi}^{2}=10$$):
  • $$2.5\ \text{pF}$$
  • $$5.0\ \text{pF}$$
  • $$25\ \text{pF}$$
  • $$50\ pF$$
The ac generator in the Figure supplies 150 $$\displaystyle V_{(max)}$$ at 50 Hz. With the switch open as shown in the diagram, the resulting current leads the generator emf by $$60^{\circ}$$. With the switch in position 1, the current lags the generator emf by $$30^{\circ}$$. When the switch is in position 2, the maximum current is 3A. Then, the value of R is:
149398.jpg
  • 50/$$\sqrt 3 \Omega$$
  • 83.3 $$\Omega$$
  • 133.3$$\Omega$$
  • 50 $$\Omega$$
An ideal choke takes a current of $$10\ Amperes$$ when connected to an ac supply of  $$125\ volt$$ and $$50\ Hz$$. A pure resistor under the same condition takes a current of  $$12.5\ Ampere$$. If the two are connected to an ac supply of $$100\sqrt {2}$$ volt and $$40\ Hz,$$  then the current in a series combination of the above resistor and inductor is:
  • $$10\ A$$
  • $$12.5\ A$$
  • $$20\ A$$
  • $$25\ A$$
For the circuit shown in the Figure, the current through the inductor is 0.9 A while the current through the condenser is 0.4 A
149697.jpg
  • current drawn from generator I = 1.13 A
  • $$\displaystyle \omega = \frac{1}{\left(1.5 LC\right)}$$
  • I = 0.5 A
  • I = 0.6 A
A broadcasting centre broadcasts at 300 metre band. A capacitor of capacitance 2.5$$\mu$$F is available. The value of the inductance required for resonant circuit is nearly
  • $$\displaystyle 1 \times 10^{-4} H$$
  • $$\displaystyle 1 \times 10^{-8} H$$
  • $$\displaystyle 1 \times 10^{-6} H$$
  • $$\displaystyle 1 \times 10^{-2} H$$
A circuit containing a $$80\ mH$$ inductor and $$60 \ \mu F$$ capacitor in series is connected to a $$230\ V, 50\ Hz$$ supply. If the resistance in the circuit is negligible then the current amplitude will be
  • 11.63 A
  • 8.23 A
  • 9.2 A
  • 13.67 A
If in a series L-C-R ac circuit, the voltages across L, C and R are $$V_1, V_2$$ and $$V_3$$ respectively, then the voltage of the source is always
  • equal to $$\displaystyle V_1+V_2+V_3$$
  • equal to $$\displaystyle V_1-V_2+V_3$$
  • more than $$\displaystyle V_1+V_2+V_3$$
  • none of the above is true
A high-impedance ac voltmeter is connected in turn across the inductor, the capacitor, and the resistance in a series circuit having an ac source of 100 V(rms) and gives the same reading in volts in each case. Then, this reading is:
  • 100/3 volts
  • 300 volts
  • 100 volts
  • incomplete data
In an ideal parallel LC circuit, the capacitor is charged by connecting it to a D.C. source which is then disconnected. The current in the circuit 
  • Becomes zero instantaneously
  • Grows monotonically
  • Decays monotonically
  • Oscillates instantaneously
An ac source producing emf  $$\displaystyle e = E_0[cos  (100 \pi t) + cos (500 \pi t)]$$ is connected in series with a capacitor and a resistor. The steady state current in the circuit is found to be $$\displaystyle i = I_1  cos  (100 \pi t + \varphi_1) + I_2  cos  (500 \pi t + \varphi_2)$$
  • $$\displaystyle I_1 > I_2$$
  • $$\displaystyle I_1 = I_2$$
  • $$\displaystyle I_1 < I_2$$
  • nothing can be said
In an electric circuit the applied alternating emf is given by $$\displaystyle E = 100\sin(314t) $$ volts and current flowing $$\displaystyle  I =  \sin  \left(314t + \dfrac{\pi}{3}\right)$$, Then, the impedance of the circuit is $$(in\ \Omega)$$
  • $$\dfrac{100}{ \sqrt{2}}$$
  • $$100$$
  • $$100 \sqrt{2}$$
  • $$None\ of\ the\ above$$
A coil of negligible resistance is connected in series with a 90 $$\Omega$$ resistor across a 120 V, 60 Hz line. An ac voltmeter reads 90 V across the resistance, then the inductance of the coil is approximately
  • 0.2 H
  • 0.3 H
  • 0.4 H
  • 0.7 H
In an ac circuit, the resistance of R $$\Omega$$ is connected in series with an inductance $$I$$. If phase angle between voltage and current be $$\displaystyle 45^{\circ}$$, the value of inductive reactance will be:
  • $$R/2$$
  • $$\displaystyle R/\sqrt 2$$
  • $$R$$
  • Insufficient data
You apply $$\displaystyle f = \frac{1}{2\pi \sqrt{LC}}$$ to find L. Which frequency will you select?
  • when $$V_R$$ is minimum
  • when $$V_R$$ is maximum
  • when $$V_C$$ is maximum
  • when $$V_C$$ is minimum
In the circuit shown in fig., the resonant frequency is
206505_6b555722aef04087aabce22638d35e7e.png
  • $$200Hz$$
  • $$220Hz$$
  • $$225.08Hz$$
  • $$230Hz$$
If resistance of $$100\Omega $$ and the inductance of $$0.5$$ henry and capacitance of $$10\times {10}^{6}$$ farad are connected  in series through $$50$$Hz A.C supp;y, then impedence is
  • $$1.8765\Omega $$
  • $$18.76\Omega $$
  • $$187.6\Omega $$
  • $$101.3\Omega $$
In which of the following circuit, there may be no change in current with increase in the frequency when same ac current is passed through them:
In an $$L-C-R$$ circuit the capacitance is changed from $$C$$ to $$4C$$. For the same resonant frequency, the inductance should be changed from $$L$$ to
  • L/4
  • L/2
  • 2L
  • 4L
In the given circuit, the current drawn from the source is
206637.PNG
  • $$20A$$
  • $$10A$$
  • $$5A$$
  • $$5\sqrt {2}A$$
The most stable frequency can be generated using
  • LC series circuit
  • LC parallel circuit
  • crystal oscillator
  • RC phase shift oscillator
With increase in frequency of an ac supply, the impedance of an $$L-C-R$$ series circuit
  • remains constant
  • increases
  • decreases
  • decrease at first becomes minimum and then increases.
Two coils $$A$$ and $$B$$ are connected in series across a $$240\ \text{V}, 50\ \text{Hz}$$ supply. The resistance of $$A$$ is $$5\ \Omega$$ and the inductance of $$B$$ is $$0.02\ \text{H}$$. The power consumed is $$3\ \text{kW}$$ and the power factor is $$0.75$$. The impedence of the circuit is
  • $$0.144\ \Omega$$
  • $$1.44\ \Omega$$
  • $$14.4\ \Omega$$
  • $$144\ \Omega$$
In a circuit inductance $$L$$ and capacitance $$C$$ are connected as shown in figure. $${A}_{1}$$ and $${A}_{2}$$ are ammeters.
When key $$K$$ is pressed to complete the circuit, then just after closing key $$(K)$$, the readings of $${A}_{1}$$ and $${A}_{2}$$ will be
206663_cb11ea8695084a2cbbc3593eef3c5206.png
  • zero in both $${A}_{1}$$ and $${A}_{2}$$
  • maximum in both $${A}_{1}$$ and $${A}_{2}$$
  • zero in $${A}_{1}$$ and maximum in $${A}_{2}$$
  • maximum in $${A}_{1}$$ and zero in $${A}_{2}$$
Capacitance $$(C)$$ of the capacitor is
  • $$10\mu F$$
  • $$15\mu F$$
  • $$20\mu F$$
  • None of these
An inductive coil has a resistance of $$100\ \Omega$$. When an a.c. signal of frequency $$1000\ Hz$$ is fed to the coil, the applied voltage leads the current by $${45}^{o}$$. What is the inductance of the coil?
  • $$10mH$$
  • $$12mH$$
  • $$16mH$$
  • $$20mH$$
An alternating voltage of $$220V,50Hz$$ frequency is applied across a capacitor of capacitance $$2\mu F$$. The impedence of the circuit is:
  • $$\cfrac{\pi}{5000}$$
  • $$\cfrac{1000}{\pi}$$
  • $${500}{\pi}$$
  • $$\cfrac{5000}{\pi}$$
The instantaneous voltage through a device of impedence $$20\Omega$$ is $$e=80\sin { 100\pi t } $$. The effective value of the current is
  • $$3A$$
  • $$2.828A$$
  • $$1.732A$$
  • $$4A$$
For watt-less power in an $$AC$$ circuit the phase angle between the current and voltage is
  • $$0^o$$
  • $$90^o$$
  • $$45^o$$
  • Not possible
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