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question_answer1) A 100 resistor is connected to a 220 V, 50 Hz ac supply. (a) What is the rms value of current in the circuit? (b) What is the net power consumed over a fully cycle?
question_answer2) (a) The peak voltage of an a.c. supply is 300 V.What is the rms voltage? (b) The rms value of current in an ac circuit is 10 A. NN hat is the peak current?
question_answer3) A 44 mH inductor is connected to 220 V. 50 Hzac supply. Determine the rms value of the current in the circuit.
question_answer4) A capacitor is connected to a 110 V, 60 Hz ac supply. Determine the rms value of the current in the circuit.
question_answer5) In Exercise 7.3 and 7.4, what is the net power absorbed by each circuit over a complete cycle. Explain your answer.
question_answer6) Obtain the resonant frequency of a series LCR circuit with L = 2.0 H, C = 32 µF and R = 10 . What is the Q-value of this circuit?
question_answer7) A charged capacitor is connected 27 mH inductor. What is the angular frequency of free oscillations of the circuit?
question_answer8) Suppose the initial charge on the capacitor in Exercise 7.7 is 6 mC. What is the total energy stored in the circuit initially? What is the total energy at later time?
question_answer9) A series LCR circuit with R = 20, L = 1.5 H and is connected to a variable frequency 200 V ac supply. When the frequency of the supply equals the natural frequency of the circuit, what is the average power transferred to the circuit in one complete cycle?
question_answer10) A radio can tune over the frequency range of a portion of MW broadcast band: (800 kHz to 1200 kHZ). If its LC circuit has an effective inductance of what must be the range of its variable capacitor? [Hint. For tuning, the natural frequency i.e., the frequency of' free oscillations for the LC circuit should be equal to the frequency of the radiowave.]
question_answer11) Figure shows a series LCR circuit connected to a variable frequency 230 V source. L = 5.0 H, R = 40. (a) Determine the source frequency which drives the circuit in resonance. (b) Obtain the impedance of the circuit and the amplitude of current at the resonating frequency. (c) Determine the rms potential drops across the three elements of the circuit. Show that the potential drop across the LC combination is zero at the resonating frequency.
question_answer12) An LC circuit contains a 20 mH inductor and a capacitor with an initial charge of 10 mC. The resistance of the circuit is negligible. Let the instant the circuit is closed be . (a) What is the total energy stored initially? Is it conserved during LC oscillations? (b) What is the natural frequency of the circuit? (e) At what time is the energy stored (i) completely electrical (i.e., stored in the capacitor)? (ii) completely magnetic (i.e., stored in the inductor)? (d) At what times is the total energy- shared equally between the inductor and the capacitor?
question_answer13) A coil of inductance 0.50 H and resistance is connected to a 240 V, 50 Hz ac supply. (a) What is the maximum current in the coil? (b) What is the time lag between the voltage maximum and the current maximum?
question_answer14) Obtain the answer (a) to (b) in Exercise 7.13 if the is connected to a high frequency supply (240 V, 10 kHz). Hence, explain the statement that at very high frequency, an inductor in a circuit nearly amounts to an open circuit. How does an inductor behave in a dc circuit after the supply state?
question_answer15) A capacitor in series with a resistance is connected to a 110 V, 60 Hz supply. (a) What is the maximum current in the circuit? (b) What is the time lag between the current maximum and the voltage maximum?
question_answer16) Obtain the answers to (a) and (b) in Exercise 7.15 if the circuit is connected to a 110 V, 12 kHz supply. Hence, explain the statement that a capacitor is a conductor at very high frequencies. Compare this behaviour with that of a capacitor in a dc circuit after the steady state.
question_answer17) Keeping the source frequency equal to the resonating frequency of the series LCR circuit, if the three elements. L, C and R are arranged in parallel, show that the total current in the parallel LCR circuit is minimum at this frequency. Obtain the current rms value in each branch of the circuit for the elements and source specified in Exercise 7.11 for this frequency.
question_answer18) A circuit containing a 80 mH inductor and a capacitor in series is connected to a 230 V, 50 Hz supply. The resistance of the circuit is negligible. (a) Obtain the current amplitude and rms values. (b) Obtain the rms values of potential drops across each element. (c) What is the average power transferred to the inductor? (d) What is the average power transferred to the capacitor? (e) What is the total average power absorbed by the circuit? [?Average? implies ?averaged over one cycle?.]
question_answer19) Suppose the circuit in Exercise 7.18 has a resistance of . Obtain the average power transferred to each element of the circuit, and the total power absorbed.
question_answer20) A series LCR circuit with is connected to a 230 V variable frequency supply. (a) What is the source frequency for which current amplitude is maximum. Obtain this maximum value. (b) What is the source frequency for which average power absorbed by the circuit is maximum. Obtain the value of this maximum power. (c) For which frequencies of the source is the power transferred to the circuit half the power at resonant frequency? What is the current amplitude at these frequencies? (d) What is the Q-factor of the given circuit?
question_answer21) Obtain the resonant frequency and Q-factor of a series LCR circuit with , and . It is desired to improve the sharpness of the resonance of the circuit by reducing its 'full width at half maximum' by a factor of 2. Suggest a suitable way.
question_answer22) Answer the following questions: (a) In any ac 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? (b) A capacitor is used in the primary circuit of an induction coil. (c) An applied voltage signal consists of a superposition of a dc voltage and an ac voltage of high frequency. The circuit consists of an inductor and a capacitor in series. Show that the dc signal will appear across C and the ac signal across L. (d) A choke coil in series with a lamp is connected to a dc line. The lamp is seen to shine brightly. Insertion of an iron core in the choke causes no change in the lamp's brightness. Predict the corresponding observations if the connection is to an ac line. (e) Why is choke coil needed in the use of fluorescent tubes with ac mains? Why can we not use an ordinary resistor instead of the choke coil?
question_answer23) pressure head is at a height of 300 m and the water flow available is . If the turbine generator efficiency is 60%, estimate the electric power available from the plant .
question_answer24) A small town with a demand of 800 kW of electric power at 220 V is situated 15 km away from an electric plant generating power at 440 V. The resistance of the two wire line carrying power is per km. The town gets power from the line through a 4000-220 V step-down transformer at a sub-station in the town, (a) Estimate the line power loss in the form of heat. (b) How much power must the plant supply, assuming there is negligible power I, due to leakage? (c) Characterise the step up transformer the plant.
question_answer25) Do the same exercise as above with the replacement of the earlier transformer by a 40,000 —220 V step-down transformer (Neglect, as before, leakage losses though, this may not be a good assumption any longer because of the very high voltage transmission involved). Hence, explain why high voltage transmission is preferred.
question_answer26) If the rms current in a 50 Hz ac circuit is 5 A, the value of the current 1/300 seconds after its value becomes zero is (a) (b) (c) (d)
question_answer27) An alternating current generator has an internal resistance and an internal reactance . It is used to supply power to a passive load consisting of a resistance and a reactance. For maximum power to be delivered from the generator to the load, the value of is equal to (a) zero (b) (c) (d)
question_answer28) When a voltage measuring device is connected to AC mains, the meter shows the steady input voltage of 220 V. This means (a) input voltage can not be AC voltage, but a DC voltage (b) maximum input voltage is 220 V (c) the meter reads not but and is calibrated to read (d) the pointer of the meter is stuck by some mechanical defect
question_answer29) To reduce the reasonant frequency in an LCR series circuit with a generator (a) the generator frequency should be reduced (b) another capacitor should be added in parallel to the first (c) the iron core of the inductor should be removed (d) dielectric in the capacitor should be removed
question_answer30) Which of the following combinations should be selected for better tuning of an LCR circuit used for communication? (a) (b) (c) (d)
question_answer31) An inductor of reactance 1 and a resistor of 2are connected in series to the terminals of a 6 V (rms) a.c. source. The power dissipated in the circuit is (a) 8 W (b) 12 W (c)14.4 W (d)18 W
question_answer32) The output of a step-down transformer is measured to be 24 V when connected to a 12 watt light blub. The value of the peak current is (a) (b) (c) 2 A (d)
question_answer33) As the frequency of an ac circuit increases, the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit ? (a) Inductor and capacitor (b) Resistor and inductor (c) Resistor and capacitor (d) Resistor, inductor and capacitor.
question_answer34) In an alternating current circuit consisting of elements in series, the current increases on increasing the frequency of supply. Which of the following elements are likely to constitute the circuit? (a) Only resistor (b) Resistor and an inductor (c) Resistor and a capacitor (d) Only a capacitor.
question_answer35) Electrical energy is transmitted over large distances at high alternating voltages. Which of the following statements is (are) correct? (a) For a given power level, there is a lower current (b) Lower current implies less power loss (c) Transmission lines can be made thinner (d) It is easy to reduce the voltage at the receiving end using step-down transformers
question_answer36) For an LCR circuit, the power transferred from the driving source to the driven oscillator is (a) Here, the power factor (b) The driving force can give no energy to the oscillator (P = 0) in some cases (c) The driving force can not syphon out (P < 0) the energy out of oscillator (d) The driving force can take away energy out of the oscillator
question_answer37) When an AC voltage of 220 V is applied to the capacitor C (a) the maximum voltage between plates is 220V (b) the current is in phase with the applied voltage (c) the charge on the plates is in phase with the applied voltage (d) power delivered to the capacitor is zero
question_answer38) The line that draws power supply to your house from street has (a) zero average current (b) 220 V average voltage (c) voltage and current out of phase by 90? (d) voltage and current possibly differing in phase such that
question_answer39) If a LC circuit is considered analogous to a harmonically oscillating spring block system, which energy of the LC circuit would be analogous to potential energy and which one analogous to kinetic energy?
question_answer40) Draw the effective equivalent circuit of the circuit shown in Fig. 4(EP).24, at very high frequencies and find the effective impedance.
question_answer41) Study the circuits (a) and (b) shown in Fig. 4(EP).26 and answer the following questions. (a) Under which conditions would the rms currents in the two circuits be the same? (b) Can the rms current in circuit (b) be larger than that in (a)?
question_answer42) Can the instantaneous power output of an ac source ever be negative? Can the average power output be negative?
question_answer43) In series LCR circuit, the plot of vs is shown in Fig. 4(EP).27. Find the bandwidth and mark in the figure.
question_answer44) The alternating current in a circuit is described by the graph shown in Fig. 4(EP).29. Show rms current in this graph.
question_answer45) How does the sign of the phase angle , by which the supply voltage leads the current in an LCR series circuit, change as the supply frequency is gradually increased from very low to very high values?
question_answer46) A device 'X' is connected to an a.c. source. The variation of voltage, current and power in one complete cycle is shown in Fig. 4(EP).31. (a) Which curve shows power consumption over a full cycle? (b) What is the average power consumption over a cycle? (c) Identify the device 'X'.
question_answer47) Both alternating current and direct current are measured in amperes. But how is the ampere defined for an alternating current?
question_answer48) A coil of henry inductance and 1 ohm resistance is connected to 200 volt, 50 Hz ac supply. Find the impedance of the circuit and time lag between max. alternating voltage and current.
question_answer49) A 60 W load is connected to the secondary of a transformer whose primary draws line voltage. If a current of A flows in the load, what is the current in the primary coil? Comment on the type of transformer being used.
question_answer50) Explain why the reactance provided by a capacitor to an alternating current decreases with increasing frequency.
question_answer51) Explain why the reactance offered by an inductor increases with increasing frequency of an alternating voltage.
question_answer52) An electrical device draws 2 kW power from AC mains [voltage 223 V (rms) = V ]. The current differs (lags) in phase by as compared to voltage. Find (i) R, (ii) , and (iii) . Another device has twice the values for R, and. How are the answers affected?
question_answer53) 1 MW power is to be delivered from a power station to a town 10 km away. One uses a pair of Cu wires of radius cm for this purpose. Calculate the fraction of ohmic losses to power transmitted if (i) power is transmitted at 220 V. Comment on the feasibility of doing this. (ii) a step-up transformer is used to boost the voltage to 11000 V, power transmitted, then a step-down transformer is used to bring voltage to 220 V.
question_answer54) Consider the LCR circuit shown in Fig. 4(EP).32. Find the net current and the phase of . Show that . Find the impedence Z for this circuit.
question_answer55) For an LCR circuit driven at frequency , the equation reads (i) Multiply the equation by and simplify where possible. (ii) Interpret each term physically. (iii) Cast the equation in the form of a conservation of energy statement. (iv) Intergrate the equation over one cycle to find that the phase difference between and must be acute.
question_answer56) In the LCR circuit shown in Fig. 4(EP).33, the ac driving voltage is (i) Write down the equation of motion for. (ii) At the voltage source stops and R is short circuited. Now write down how much energy is stored in each of L and C. (iii) Describe subsequent motion of charges.
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