Answerthe following questions:
(a) In anyac circuit, is the applied instantaneous voltage equal to thealgebraic sum of the instantaneous voltages across the serieselements of the circuit? Is the same true for rms voltage?
(b) A capacitor is used in the primarycircuit of an induction coil.
(c) Anapplied voltage signal consists of a superposition of a dc voltageand an ac voltage of high frequency. The circuit consists of aninductor and a capacitor in series. Show that the dc signal willappear across C andthe ac signal across L.
(d) Achoke coil in series with a lamp is connected to a dc line. The lampis seen to shine brightly. Insertion of an iron core in the chokecauses no change in the lamp’s brightness. Predict thecorresponding observations if the connection is to an ac line.
(e) Why ischoke coil needed in the use of fluorescent tubes with ac mains? Whycan we not use an ordinary resistor instead of the choke coil?
Answerthe following questions:
(a) In anyac circuit, is the applied instantaneous voltage equal to thealgebraic sum of the instantaneous voltages across the serieselements of the circuit? Is the same true for rms voltage?
(b) A capacitor is used in the primarycircuit of an induction coil.
(c) Anapplied voltage signal consists of a superposition of a dc voltageand an ac voltage of high frequency. The circuit consists of aninductor and a capacitor in series. Show that the dc signal willappear across C andthe ac signal across L.
(d) Achoke coil in series with a lamp is connected to a dc line. The lampis seen to shine brightly. Insertion of an iron core in the chokecauses no change in the lamp’s brightness. Predict thecorresponding observations if the connection is to an ac line.
(e) Why ischoke coil needed in the use of fluorescent tubes with ac mains? Whycan we not use an ordinary resistor instead of the choke coil?
(a) Yes; thestatement is not true for rms voltage
Itis true that in any ac circuit, the applied voltage is equal to theaverage sum of the instantaneous voltages across the series elementsof the circuit. However, this is not true for rms voltage becausevoltages across different elements may not be in phase.
(b) High inducedvoltage is used to charge the capacitor.
Acapacitor is used in the primary circuit of an induction coil. Thisis because when the circuit is broken, a high induced voltage is usedto charge the capacitor to avoid sparks.
(c) The dc signal will appear across capacitor Cbecause for dc signals, the impedance of an inductor (L) isnegligible while the impedance of a capacitor (C) is very high(almost infinite). Hence, a dc signal appears across C. For anac signal of high frequency, the impedance of L is high andthat of C is very low. Hence, an ac signal of high frequencyappears across L.
(d) If an iron core is inserted in the choke coil (which is inseries with a lamp connected to the ac line), then the lamp will glowdimly. This is because the choke coil and the iron core increase theimpedance of the circuit.
(e) A choke coil is needed in the use of fluorescent tubeswith ac mains because it reduces the voltage across the tube withoutwasting much power. An ordinary resistor cannot be used instead of achoke coil for this purpose because it wastes power in the form ofheat.
(a) Yes; thestatement is not true for rms voltage
Itis true that in any ac circuit, the applied voltage is equal to theaverage sum of the instantaneous voltages across the series elementsof the circuit. However, this is not true for rms voltage becausevoltages across different elements may not be in phase.
(b) High inducedvoltage is used to charge the capacitor.
Acapacitor is used in the primary circuit of an induction coil. Thisis because when the circuit is broken, a high induced voltage is usedto charge the capacitor to avoid sparks.
(c) The dc signal will appear across capacitor Cbecause for dc signals, the impedance of an inductor (L) isnegligible while the impedance of a capacitor (C) is very high(almost infinite). Hence, a dc signal appears across C. For anac signal of high frequency, the impedance of L is high andthat of C is very low. Hence, an ac signal of high frequencyappears across L.
(d) If an iron core is inserted in the choke coil (which is inseries with a lamp connected to the ac line), then the lamp will glowdimly. This is because the choke coil and the iron core increase theimpedance of the circuit.
(e) A choke coil is needed in the use of fluorescent tubeswith ac mains because it reduces the voltage across the tube withoutwasting much power. An ordinary resistor cannot be used instead of achoke coil for this purpose because it wastes power in the form ofheat.
