Test D - Alternating Current (AC) Assignment - Notes - Class 12

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1. What is the phase difference between voltage and current in LCR series circuit at resonance. [1]
2. Explain why average power in an a.c. circuit containg only capacitor is zero. [1]
3. Find the angular frequency of a charge oscillating in an LC circuit of L = 5H and C = 300 µF. [1]
4. A bulb and a capacitor in series are connected to a variable frequency source. How will the brightness of
the bulb change on increasing the frequency. [1]
5. Define Q factor and write is formula. [2]
6. Derive expression of impedance in LCR circuit and derive expression for the phase difference between
voltage and current by phasor diagram. [2]
7. An inductor coil, a capacitor and a resistance of 2.0 H, 18 µF and 10 k ? respectively are connected to an
a.c. source of 20 V with adjustable frequency.
(a) What frequency should be chosen to maximise the current
(b) What is the value of this maximum current. [2]
8. Derive expression for average power in an a.c. circuit containing only resistance. [2]
9. The peak value of alternating current is 5A and its frequency is 60 Hz. Find its rms value. How long will the
current take to reach the peak value starting from rest. [2]
10. In the given circuit, the potential difference across the inductor L and resistor R are 200 V and
150 V respectively and the r.m.s. value of current is 5A. Calculate (i) the impedance of the circuit and
(ii) the phase angle between the voltage and the current. [2]
11. A resistor of 200 ? and a capacitor of 15.0 µF are connected in series to a 220 V , 50 Hz ac source.
Calculate (a) the current in the circuit (b) the rms voltage across the resistor and the capacitors.
Is the algebraic sum of these voltage more than the source voltage ? If yes, why ? [3]
12. A LCR series circuit with L = 100 mH, C = 100 µF and R = 120 ? are connected to an a.c. source of
E = (30 V) sin (100 s
–1
) t. Find the impedance, the peak current and the resonant frequency of the circuit.
[3]
13. An alternating current of 1.5 mA and angular frquency 300 radian/sec flows through a 10 k ? resistance
and 0.50 µF capacitor in series
(i) Find the rms voltage drop across capacitor
(ii) phase differene
(iii) impedance. [3]
ALTERNATING CURRENT T E S T - D
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