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

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.

View Answer

Answer:The driving force can take away energy out of the oscillator.

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.

View Answer

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.

View Answer

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.

View Answer

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.

View Answer

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.

View Answer

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.

View Answer

Answer:the meter reads not v but < v² > and is . calibrated to read √< v² > .

9 An alternating current generator has an internal resistance R_g and an internal reactance X_g. It is used to supply power to a passive load consisting of a resistance R_g and a reactance X_L For maximum power to be delivered from the generator to the load, the value of X_L is equal to

A zero.

B Xg.

C -Xg.

D Rg.

View Answer

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

C 5/6 A

D 5√2A

View Answer

Answer:B

11 The natural frequency (ca0) of oscillations in LC circuit is given by

A

B

C

D √LC

View Answer

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

View Answer