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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 601. |
The natural frequency `(omega_(0))` of oscillations in LC circuit is given byA. `(1)/(2pi)(1)/(sqrt(LC))`B. `(1)/(pi)(1)/(sqrt(2LC))`C. `(1)/(sqrt(LC))`D. `sqrt(LC)` |
| Answer» Correct Answer - C | |
| 602. |
In an LCR series a.c. Circuit the voltage across each of hte components L,C and R is 50V. The voltage across the LC combination will beA. 50 VB. `50sqrt(2) V`C. `100 V`D. `0 V` (zero) |
| Answer» Correct Answer - d | |
| 603. |
In an AC circuit `I=100sin 200pit`. The time required for the current to achieve its peak value of will beA. `1/100 sec`B. `1/200 sec`C. `1/300 sec`D. `1/400 sec` |
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Answer» Correct Answer - D The currents takes `T/4` sec to reach the peak value. In the given question `(2pi)/T=200pi implies T=1/100sec` `:.` Time to reach the peak value `=1/400sec` |
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| 604. |
In an ac circuit `l=100 sin 200 pi t` . The time required for the current to achieve its peak value will beA. `1/100 sec`B. `1/200 sec`C. `1/300 sec`D. `1/400 sec` |
| Answer» Correct Answer - d | |
| 605. |
Reactance of an inductor of `1/(pi)` henry at `50Hz` frequency isA. `50/pi ohm`B. `pi/50 ohm`C. `100 ohm`D. `50 ohm` |
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Answer» Correct Answer - C `X_(L)=2pivL=2xxpixx50xx1/(pi)=100 Omega` |
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| 606. |
An inductance of `1mH` a condenser of `0.5` henry and capacitance of `10xx10^(-6)F` are connected in series through `50Hz` AC supply, then impedence isA. `100 Omega`B. `30 Omega`C. `3.2 Omega`D. `10 Omega` |
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Answer» Correct Answer - D Given `omegaL=1/(omegaC)implies omega^(2)=1/(LC)` or `omega=1/(sqrt(10^(-3)xx10xx10^(-6)))=1/(sqrt(10^(-8)))=10^(4)` `X_(L)=omega L =10^(4)xx10^(-3)=10Omega` |
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| 607. |
In an `AC` circuit, peak value of voltage is `423` volts. Its effective voltage isA. 400 voltsB. 323 voltsC. 300 voltsD. 340 volts |
| Answer» Correct Answer - c | |
| 608. |
If instantaneous current is given by `i=4 cos(omega t + varphi)` amperes, then the `r.m.s.` value of current isA. 4 amperesB. `2sqrt(2)` amperesC. `4sqrt(2)` amperesD. Zero amperes |
| Answer» Correct Answer - b | |
| 609. |
If instantaneous current is given by `i=4 cos(omega t + varphi)` amperes, then the `r.m.s.` value of current isA. `4` ampereB. `2sqrt(2)` ampereC. `4sqrt(2)` ampereD. Zero ampere |
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Answer» Correct Answer - B `i_(rms)=(i_(0))/(sqrt(2))=4/(sqrt(2))=2sqrt(2)` ampere |
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| 610. |
An alternating emf given by equation `e=300sin(100pi)t V` is applied to a resistance `100 Omega`. The rms current through the circuit is (in amperes).A. `3/sqrt(2)`B. `9/sqrt(2)`C. 3D. `6/sqrt(2)` |
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Answer» Correct Answer - A The given equation, e=`300 sin (100pi)t]`..............(i) We know that, `e=e_(0)sinomegat`............(ii) On comparing Eqs (i) and (ii), we get `e_(0)` = 300 V and `R= 100Omega` The rms current through the circuit `I_(rms) =?` `I_(rms) = e_(0)/sqrt(2R) = 300/(sqrt(2) xx 100) = 3/sqrt(2)` A |
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| 611. |
In an `LR`-circuit, the inductive reactance is equal to the resistance `R` of the circuit. An e.m.f `E=E_(0)cos (omegat)` applied to the circuit. The power consumed in the circuit isA. `E_(0)^(2)/(R)`B. `E_(0)^(2)/(R)`C. `E_(0)^(2)/(4R)`D. `E_(0)^(2)/(8R)` |
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Answer» Correct Answer - C |
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| 612. |
In an `LR`-circuit, the inductive reactance is equal to the resistance `R` of the circuit. An e.m.f `E=E_(0)cos (omegat)` applied to the circuit. The power consumed in the circuit isA. `E_(0)^(2)/R`B. `E_(0)^(2)/(2R)`C. `E_(0)^(2)/(4R)`D. `E_(0)^(2)/(8 R)` |
| Answer» Correct Answer - c | |
| 613. |
In an `LR`-circuit, the inductive reactance is equal to the resistance `R` of the circuit. An e.m.f `E=E_(0)cos (omegat)` applied to the circuit. The power consumed in the circuit isA. `E_(0)^(2)/(sqrt(2R)`B. `(E_(0)^(2))/(4R)`C. `(E_(0)^(2))/(2R)`D. `(E_(0)^(2))/(8R)` |
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Answer» Correct Answer - B `underset(L)(X)` = R `therefore` Z = `sqrt 2`R P = `(underset(rms)(V)/Z)^(2)`.R = `(underset(o)(E)/sqrt 2/ sqrt 2R)^(2)`.R = `underset(o)(E)^(2)/4R` |
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| 614. |
In an LR circuit , the phase angle between alternating voltage and alternating current is `45^@`. The value of inductive reactance will beA. `R/4`B. `R/2`C. RD. data insufficient |
| Answer» Correct Answer - C | |
| 615. |
The r.m.s current in an `AC` circuit is `2A`. If the wattless current be `sqrt(3)A`, what is the power factor?A. `1/(sqrt(3))`B. `1/(sqrt(2))`C. `1/2`D. `1/3` |
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Answer» Correct Answer - C `i_(WL)=i_(rms) sin varphi implies sqrt(3) =2sin varphi implies sin varphi=(sqrt(3))/2` `implies varphi=60^(@)` so `p.f=cos varphi=cos 60^(@)=1/2` |
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| 616. |
The electrical analog of a spring constant k isA. LB. RC. CD. `(1)/(C)` |
| Answer» Correct Answer - D | |
| 617. |
A series `AC` circuit consists of an inductor and a capacitor. The inductance and capacitance is respectively `1`henry and `25 muF` if the current is maximum in circuit then angular frequency will beA. `200`B. `100`C. `50`D. `200//2pi` |
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Answer» Correct Answer - A Current in `LC` circuit becomes maximum when resonance occurs. So, `omega=1/(sqrt(LC))=1/(sqrt(1xx25xx10^(-6)))=1000/5=200rad//sec` An alternating e.m.f of frequency is `v(=1/(2pisqrt(LC)))` |
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| 618. |
A charged capacitro and an inductor are connected in series. At time t = 0 , the current is zero but the capacitor is charged, If T is the period of resulting oscillations, then the time after which current in the circuit becomes maximum , isA. TB. `(T)/(4)`C. `(T)/(2)`D. `(T)/(6)` |
| Answer» Correct Answer - B | |
| 619. |
A circuit has a resistance of `50 ohms` and an inductance of `3/pi` henry.It is connected in series with a condenser of `40/pi muF` and `AC` supply voltage of `200 V` and `50` cycles/sec.Calculate (i)the impedance of the circuit. (ii)the p.d. across inductor coil and condenser. (iii)Power factor |
| Answer» Correct Answer - `Z=50sqrt2 ohm,V_(C)=500sqrt2` volt and `V_(L)=600sqrt2` volt, `1/sqrt2` | |
| 620. |
The phase difference between voltage and current in series L-C circuit isA. `0^(@)`B. `pi`C. `(pi)/(2)`D. `(pi)/(3)` |
| Answer» Correct Answer - C | |
| 621. |
In an electric iron heat producedm is same, whether it is connected across an A.c. source or across 50 V constant voltage. R.M.S. value of the A.C. voltage applied isA. 50 VB. ZeroC. `50sqrt(2)V`D. `(50)/(sqrt(2))V` |
| Answer» Correct Answer - A | |
| 622. |
A combination of elements is enclosed in a black box an the voltage and currents are measured across this black box. The expression for applied voltage, and the current flowing in it is `V = V_(0) sin omega t`, `i = 2 sqrt(2) sin (omega + pi//4)` where `omega = 100 pi "rad"//"sec"` Then the wrong statement is A. The must be a capacitor is the black boxB. Power factor of circuit = 0.707C. There must be a resistor in the boxD. There must be an inductor in the box |
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Answer» Correct Answer - D Since current leads voltage by `45^(@)`, there mustbe a resistor and a capacitor. We can say nothing about inductor surely. It may or may not be present. |
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| 623. |
When an alternating voltage of `220 V` is applied across a device `P`, a current of `0.25 A` flows through the circuit and it leads the applied voltage by a angle `pi/2` radian. When the same voltage source is connected across another device `Q`, the same current is observed in the circuit but in phase with the applied voltage. What is the current when the same source is connected across a series combination of `P` and `Q`?A. 1/4`sqrt 2` A lagging in phase by `pi`/4 with voltageB. 1/4`sqrt 2` A leading in phase by `pi`/4 with voltageC. `1/sqrt 2`A leading in phase by `pi`/4 with voltageD. `1/sqrt 2` A leading in phase by `pi`/6 with voltage |
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Answer» Correct Answer - B P is a capacitor, `X_C = 220 / 0.25 = 880 Omega` Q is resistance, `R = 220 / 0.25 = 880 Omega` When P and Q are in series, Z = `sqrt (R^(2) + X_C^(2))` = `880sqrt 2 Omega` `phi = tan^(-1)(X_C/R) = 45^(@)` (current leading ) `t = V / Z = 1 / 4sqrt 2` A |
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| 624. |
In a certain circuit current changes with time according to `i=2sqrt(t)` RMS value of current between t=2s to t=4s will beA. 3AB. `3sqrt(3)`AC. `2sqrt(3)`D. `sqrt(3)`A |
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Answer» Correct Answer - C `i_(rms)^(2) = (int i^(2)dt)/(int dt)` `=(int_(2)^(4)dt)/(int_(2)^(4)dt) = (4int_(2)^(4)tdt)/(2)= 2[t^(2)/2]_(-2)^(4) = 12A^(2)` `rArr i_(rms) = 2sqrt(3)A` |
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| 625. |
An alternating voltage V=140 sin 50 t is applied to a resistor of resistance 10 `Omega`. This voltage produces `triangleH` heat in the resistor in time `trianglet`. To produce the same heat in the same time, rquired DC current isA. 14 AB. About 20 AC. about 10 AD. None of these |
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Answer» Correct Answer - C `I_(0) = 140/10 = 14A` `therefore I_(rms)= I_(0)/sqrt(2) = 10 A` `therefore I_(DC)` required will be approximateley 10 A |
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| 626. |
For the L-R-C series circuit described in the above Illustration 5.7, describe the time dependence of the instantaneous current and each instantaneous voltage. |
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Answer» we found the amplitude of the current and voltages. Now we have to find the expressions for the instantaneous values of the current and voltages. As we learned, the voltage across a resistor is in phases with the current but the voltages across an inductor or capacitor are not. We also learned in this section that `phi` is the phase angle between the source voltage and the current. The current and all the voltage oscillate with the same angular frequency. Let us choose `E=E_(0)sin omega t implies E=50 sin(10,000 t)` then `I_I_(0) sin (10,000 t+ phi)`, where `phi= -53^(@)=-(53xxpi)/(180) rad = -0.93 rad` `implies I=0.10 sin (10,000 t-0.93)` Current and voltage are in phase in resistor so `V_(R)=V_(R0) sin (10,000t-0.93)=30 sin(10,000 t-0.93)` In inductor voltage voltage leads current by `pi//2` so , `V_(L)=V_(L0) sin [10,000t-0.93+(pi//2)]=60 cos(10,000 t-0.93)` In capcitor voltage lags currents lags currents by `(pi//2)` so `V_(C)=V_(C0) sin[10,000t-0.93+(pi//2)]` `=-20 cos (10,000t-0.93)`. |
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| 627. |
The power factor of a circuit isA. Z/RB. R/ZC. R/XD. X/R |
| Answer» Correct Answer - B | |
| 628. |
In an AC circuit , `underset(o)(V)` , `underset(o)(I)` and cos`theta` are voltage amplitude , current amplitude and power factor respectively, the power consumption isA. 1/2`underset(o)(V)``underset(o)(I)` cos`theta`B. `(1/sqrt(2)) V_(0)I_(0)costheta`C. `V_(0)I_(0)costheta`D. `(1/sqrt(2))V_(0)I_(0)sintheta` |
| Answer» Correct Answer - A | |
| 629. |
The reciprocal of impedance is calledA. reactanceB. admittanceC. inductanceD. conductance |
| Answer» Correct Answer - B | |
| 630. |
An electric heater rated 220 V and 550 V is connected to AC mains. The current drawn by it isA. 0.8 AB. 2.5 AC. 0.4 AD. 1.25 A |
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Answer» Correct Answer - B P = VI I = P/V = 550/220 = 2.5 A |
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| 631. |
What is increase in step-down transformer?A. VoltageB. CurrentC. PowerD. Current density |
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Answer» Correct Answer - B In step down transformer , `underset(P)(V)` gt `underset(S)(V)` but, `underset(P)(V)`/`underset(S)(V)` = `underset(S)(I)`/`underset(P)(I)` `therefore` `underset(S)(I)` gt `underset(P)(I)` So, current in the secondary coil is greater than the primary. |
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| 632. |
A step up transformer is used toA. increase the current and increase the voltageB. decrease the currentd and increase the voltageC. increase the current and decrease the voltageD. decrease the current and decrease the voltage |
| Answer» Correct Answer - 2 | |
| 633. |
A transformer changes the voltageA. without changing the current and frequencyB. without changing the current but changes the frequencyC. without changing the frequency but changesf the currentD. without changing the frequency as well as the current |
| Answer» Correct Answer - 3 | |
| 634. |
The transformer ratio of a step up transformer isA. greater than oneB. less than oneC. less than one and some times greater than oneD. greater than one and some times less than one |
| Answer» Correct Answer - 1 | |
| 635. |
A step up transformer is connected on the primary side to a rechargable battery which can deliver a large current. If a bulb is connected in the secondary, thenA. the bulb will glow very brightB. the bulb will get fusedC. the bulb will glow, but with less brightnessD. the bulb will not glow |
| Answer» Correct Answer - 4 | |
| 636. |
In a step down transformer, the number of turns in the primary is alwaysA. greater than the number of turns in the secondaryB. less than the number of turns in the secondaryC. equal to the number of turns in the secondaryD. either greater than or less than the number of turns in the secondary |
| Answer» Correct Answer - 1 | |
| 637. |
Write the expression for the reactance of (i) an inductor and (ii) a capacitor. |
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Answer» (i) Inductive reactance `(X_(L))= omega L` (ii) Capacitive reactance `(X_(C ))=(1)/(omega C)` |
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| 638. |
Assertion: Average value of `AC` over a complete cycle is always zero. Reason: Average value of `AC` is always defined over half cycle.A. If both assertion and reason are true and the reason is the correct explanation of the assertion.B. If both assertion and reason are true but reason is not the correct explanation of the a ssertion.C. If assertion is true but reason is false.D. If the assertion and reason both are false. |
| Answer» Correct Answer - b | |
| 639. |
Assertion: Average value of `AC` over a complete cycle is always zero. Reason: Average value of `AC` is always defined over half cycle.A. If both the assertion and reason are true and reason is a true explantion of the assertion.B. If both the assertion and reason are true but the reason is not true the correct explantion of the assertion.C. If the assertion is true but reason falseD. If both the assertion and reason are false. |
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Answer» Correct Answer - B For half cycle `I_(mean)=0.636 I_(0)` or `E_(mean)=0.636 E_(0)` Average value is always defined over a half cycle cause in next half cycle it will be opposite in direction. Hence for one complete cycle, average value will be zero. |
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| 640. |
Assertion: `AC` is more dangerous than `DC` Reason: Frequency of `AC` is dangerous for humban body.A. If both the assertion and reason are true and reason is a true explantion of the assertion.B. If both the assertion and reason are true but the reason is not true the correct explantion of the assertion.C. If the assertion is true but reason falseD. If both the assertion and reason are false. |
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Answer» Correct Answer - A The effect of `AC` on the body depends largely on the frequency. Low frequency currents of `50` to `60 Hz`(cycles/sec), which are commonly used, are usually more dangerous than high frequency currents and are `3` to `5` times more dangerous than `DC` of same voltage and amperage (current). The usual frequency of `50`cps (or `60` cps) is extermely dangerous as it corresponds to the fibrillation frequency of the myocardium. This results in ventricular fibrillation and instant death |
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| 641. |
Assertion: `AC` is more dangerous than `DC` Reason: Frequency of `AC` is dangerous for humban body.A. If both assertion and reason are true and the reason is the correct explanation of the assertion.B. If both assertion and reason are true but reason is not the correct explanation of the a ssertion.C. If assertion is true but reason is false.D. If the assertion and reason both are false. |
| Answer» Correct Answer - a | |
| 642. |
Statement 1: Both dc and ac can be measured by a hot wire instrument. Statement 2: the hot wire instrument is based on the principle of magnetic effect of current.A. If both the assertion and reason are true and reason is a true explantion of the assertion.B. If both the assertion and reason are true but the reason is not true the correct explantion of the assertion.C. If the assertion is true but reason falseD. If both the assertion and reason are false. |
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Answer» Correct Answer - C Both `AC` and `DC` produce heat, which is proportional to square of the current. The reversal of direction of current in `AC` is immaterial so far as production of heat is concerned. |
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| 643. |
Statement 1: Both dc and ac can be measured by a hot wire instrument. Statement 2: the hot wire instrument is based on the principle of magnetic effect of current.A. If both assertion and reason are true and the reason is the correct explanation of the assertion.B. If both assertion and reason are true but reason is not the correct explanation of the a ssertion.C. If assertion is true but reason is false.D. If the assertion and reason both are false. |
| Answer» Correct Answer - c | |
| 644. |
Statement 1: An alternating current shown magnetic effect. Statement 2: Alternating current varies with time .A. If both assertion and reason are true and the reason is the correct explanation of the assertion.B. If both assertion and reason are true but reason is not the correct explanation of the a ssertion.C. If assertion is true but reason is false.D. If the assertion and reason both are false. |
| Answer» Correct Answer - b | |
| 645. |
Statement 1: An alternating current shown magnetic effect. Statement 2: Alternating current varies with time .A. If both the assertion and reason are true and reason is a true explantion of the assertion.B. If both the assertion and reason are true but the reason is not true the correct explantion of the assertion.C. If the assertion is true but reason falseD. If both the assertion and reason are false. |
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Answer» Correct Answer - B Like direct current, alternating current also produces magnetic field. But the magnitude and direction of the field goes on changing continuously with time. |
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| 646. |
Assertion : An alternating current does not show any magnetic effect. Reason : Alternating current does not vary with time.A. If both assertion ans reason are true ans reaason is the correct explanation of assertion.B. If both assertion and reason are true but reason is not the correct explanation of assertion.C. If assertion istrue but reason is false.D. If both assertion and reason are false. |
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Answer» Correct Answer - C Like direct current, an alternating current also produces magnetic field. But the magnitude and direction of the field goes on changing continuously with time. |
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| 647. |
Statement 1: An alternating current shown magnetic effect. Statement 2: Alternating current varies with time .A. If both assertion and reason are true and the reason is the correct explanation of the assertion.B. If both assertion and reason are true but reason is not the correct explanation of the a ssertion.C. If assertion is true but reason is false.D. If the assertion and reason both are false. |
| Answer» Correct Answer - b | |
| 648. |
In the circuit diagram shown in figure, 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 after some time. Choose the correct option(s) A. Current in the indcutor when the circuit reaches the new steady state is 4A.B. The net change in the magnitic flux is the inductor is 1.5WbC. The net change in the magnetic flux in the conductor is 9volt when the circuit reaches the new steady state.D. The charge stored in the capacitor in the new steady state is 1.2mC |
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Answer» Correct Answer - A::B |
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| 649. |
An AC circuit contains a resistance R, an inductance L and a capacitance C connected in series across an alternator of constant voltage and variable frequency. At resonant frequency, it is found that the inductive reactance, the capacitive reactance and the resistance are equal and the current in the circuit is `i_(0)`. Find the current in the circuit at a frequency twice that of the resonant frequency. |
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Answer» At Resonance `R = omega_(0)L=(1)/(omega_(0)C)` At `f=2f_(0),omega_(0)L=2pi fL=2pi(2f_(0))L` `= 2 omega_(0)L=2R` `f = 2f_(0)`, `(i)/(omega C)=(1)/(2pi fC)=(11)/(2pi(2f_(0))C)=(1)/(2).(1)/(omega_(0)C)=(R )/(2)` current (i) `= (E_(0))/(Z)` `i = (i_(0)R)/(sqrt(R^(2)+(omega L-(I)/(omega C))^(2)))` `i=(i_(0)R)/(sqrt(R^(2)+(2R-(R )/(2))^(2))) " " (because E_(0)=i_(0)R)` `= (i_(0)R)/(sqrt(R^(2)+(9R^(2))/(4)))=(2i_(0)R)/(R sqrt(13))` `i = (2i_(0))/(sqrt(13))` |
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| 650. |
What is the phase difference between A.C emf and current in the following : Pure resistor, pure inductor and pure capacitor. |
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Answer» (i) In pure resistor A.C. e.m.f and current are in phase with each other. (ii) In pure inductor, current lags behind the e.m.f. by an angle of `(pi)/(2)` (or) `90^(@)`. (iii) In pure capacitor, current leads the e.m.f by an angle `(pi)/(2)` (or) `90^(@)`. |
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