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Objective Type Question Answers On Class 12 Physics Chapter 7 Alternating Current

Questions
1 When an AC voltage of 220 V is applied to the capacitor C
A the maximum voltage between plates is 220 V.
B the current is in phase with the applied voltage.
C the charge on the plates is not in phase with the applied voltage.
D power delivered to the capacitor is zero.

Answer:power delivered to the capacitor is zero.
2 For an LCR circuit, the power transferred from the driving source to the driven oscillator is P = I²Z cos Φ. Which of the following is incorrect?
A Here, the power factor cos Φ ≥ 0, P ≥ 0.
B The driving force can give no energy to the oscillator (P = 0) in some cases.
C The driving force cannot syphon out (P < 0) the energy out of oscillator.
D The driving force can take away energy out of the oscillator.

Answer:The driving force can take away energy out of the oscillator.
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3 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? [NCERT Exemplar]
A Inductor and capacitor.
B Resistor and inductor.
C Resistor and capacitor.
D Inductor only.

Answer:Inductor and capacitor.
4 The output of a step-down transformer is measured to be 24 V when connected to a 12 watt light bulb. The value of the peak current is
A 1/√2 A.
B √2A.
C 2 A.
D 2√2 A.

Answer:1/√2 A.
5 An inductor of reactance 1 Ω and a resistor of 2 Ω are 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.

Answer:14.4 W.
6 Which of the following combinations should be selected for better tuning of an LCR circuit used for communication?
A R = 20, L= 1.5 H, C = 35 μF.
B R = 25 , L = 2.5 H, C = 45 μF.
C R = 15 , L = 3.5 H, C = 30 μF.
D R = 25 , L = 1.5 H, C = 45 μF.

Answer:R = 15 , L = 3.5 H, C = 30 μF.
7 To reduce the resonant 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.

Answer:another capacitor should be added in parallel to the first.
8 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 cannot be AC voltage, but a DC voltage.
B maximum input voltage is 220V.
C the meter reads not v but < v² > and is . calibrated to read √< v² > .
D the pointer of the meter is stuck by some mechanical defect.

Answer:the meter reads not v but < v² > and is . calibrated to read √< v² > .
9 An alternating current generator has an internal resistance Rg and an internal reactance Xg. It is used to supply power to a passive load consisting of a resistance Rg and a reactance XL For maximum power to be delivered from the generator to the load, the value of XL is equal to
A zero.
B Xg.
C -Xg.
D Rg.

Answer:-Xg.
10 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 5√2A
B Class 12 Physics Chapter 7 Alternating Current
C 5/6 A
D 5√2A

Answer:B
11 The natural frequency (ca0) of oscillations in LC circuit is given by
A Class 12 Physics Chapter 7 Alternating Current
B Class 12 Physics Chapter 7 Alternating Current
C Class 12 Physics Chapter 7 Alternating Current
D √LC

Answer:C
12 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 inductor
C Resistor and capacitor
D Only inductor

Answer:Resistor and capacitor
13 In the case of an inductor
A voltage lags the current by π/2
B voltage leads the current by π/2
C voltage leads the current by π/3
D voltage leads the current by π/4

Answer:voltage leads the current by π/2
14 The phase relationship between current and voltage in a pure resistive circuit is best represented by
A Class 12 Physics Chapter 7 Alternating Current
B Class 12 Physics Chapter 7 Alternating Current
C Class 12 Physics Chapter 7 Alternating Current
D Class 12 Physics Chapter 7 Alternating Current

Answer:B
15 Reciprocal of impedance is
A susceptance
B conductance
C admittance
D transconductance

Answer:admittance
16 The power factor varies between
A 2 and 2.5
B 3.5 to 5
C 0 to 1
D 1 to 2

Answer:0 to 1
17 Average power generated in an inductor connected to an a.c. source is
A Class 12 Physics Chapter 7 Alternating Current
B LI²
C zero
D None of these

Answer:zero
18 Alternating current cannot be measured by dc ammeter, because
A ac cannot pass through ac ammeter.
B ac charges direction.
C average value of current of complete cycle is zero.
D ac ammeter will get damaged.

Answer:ac cannot pass through ac ammeter.
19 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 are in phase.

Answer:zero average current.
20 The reactance of a capacitor C is X. If both the frequency and capacitance be doubled, then new reactance will be
A X
B 2X
C 4X
D X/4

Answer:X/4

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