JEE Physics Alternating Current MCQs Set B

Question:

• a)

  

• b)

  

• c)

  

• d) Zero

Answer:

Question:  A coil has resistances 30 ohm and inductive reactance 20 ohm at 50 Hz frequency. If an AC source, of 200 volt, 100 Hz is connected across the coil, the current in the coil will be

• a) 4.0 A
• b) 8.0 A
• c) 2.0 A
• d)

  

Answer: 4.0 A

Question: An L-C-R circuit is connected to a source of A.C. current. At resonance, the phase difference between the applied voltage and the current in the circuit, is

• a) Zero
• b)

  

• c)

  

• d)

  

Answer:  Zero

Question: The value of quality factor is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A capacitor of capacity C has reactance X. If capacitance and frequency become double then reactance will be

• a)

  

• b)

  

• c) 4X
• d) 2X

Answer: 

Question: For a series LCR circuit the power loss at resonance is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: In a circuit L, C and R are connected in series with an alternating voltage source of frequency f. The current leads the voltage by 45°. The value of C is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a) 0.80
• b) 0.64
• c) 0.56
• d) 0.33

Answer: 0.80

Question:

• a)

  

• b)

  

• c)

  

• d) None of these

Answer:

Question:

• a) 220 V, 2.2 A
• b) 220 V, 2.0 A
• c) 150 V, 2.2 A
• d) 100 V, 2.0 A

Answer:  220 V, 2.2 A

More Questions..............................

Question: A capacitor and a bulb are connected in series with a source of alternating emf. If a dielectric slab is inserted between the plates of the capacitor, then

• a) The brightness of the bulb increases
• b) The brightness of the bulb becomes zero
• c) The brightness of the bulb decreases
• d) The brightness of the bulb remains same

Answer: The brightness of the bulb increases

Question: The primary winding of a transformer has 500 turns whereas its secondary has 5000 turns. The primary is connected to an A.C. supply 20 V, 50 Hz. The secondary will have an output of

• a) 200 V, 50 Hz
• b) 200 V, 500 Hz
• c) 2 V, 5 Hz
• d) 2 V, 50 Hz

Answer:  200 V, 50 Hz

Question:

• a) 120 volt
• b) 220 volt
• c) 30 volt
• d) 90 volt

Answer: 120 volt

Question: A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, then the efficiency of the transformer is approximately

• a) 90%
• b) 50%
• c) 10%
• d) 30%

Answer: 90%

Question:

• a) 100 mH
• b) Cannot be calculated unless R is known
• c) 1 mH
• d) 10 mH

Answer: 100 mH

Question: A 220 volt input is supplied to a transformer. The output circuit draws a current of 2.0 ampere at 440 volts. If the efficiency of the transformer is 80%, the current drawn by the primary windings of the transformer is

• a) 5.0 ampere
• b) 3.6 ampere
• c) 2.8 ampere
• d) 2.5 ampere

Answer: 5.0 ampere

Question: A step-up transformer operates on 220 V line and supplies 2.2 A. The ratio of primary and secondary winding is 11 : 50. The output voltage in the secondary is

• a) 1000 V
• b) Zero
• c) 100 V
• d) 220 V

Answer: 1000 V

Question: A coil of self inductance L is connected in series with a bulb and an A.C. source. Brightness of the bulb decreases when

• a) An iron rod is inserted in the coil
• b) Frequency of the A.C. source is decreased
• c) Number of turns in the coil is reduced
• d) 

  

Answer: An iron rod is inserted in the coil

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6A, the voltage across the secondary coil and the current in the primary coil respectively are

• a) 450 V, 15 A
• b) 450 V, 13.5 A
• c) 600 V, 15 A
• d) 300 V, 15 A

Answer: 450 V, 15 A

Question:

• a) 0.5 A
• b) Approximately 1 A
• c) 1.5 A
• d) 0.7 A

Answer: 0.5 A

Question:

• a)

  

• b)

  

• c)

  

• d) 0

Answer:

Question:

• a) 4
• b) 2
• c) 1
• d) 3

Answer:  4

Question:

• a) 0.4
• b) 0.6
• c) 1.2 A
• d)

  

Answer:  0.4

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a) A₃
• b) A₂
• c) A₁
• d) None of these

Answer: A₃

Question: Average energy loss due to inductance (L) of circuit is (symbols have their usual meaning)

• a) Zero
• b)

  

• c)

  

• d)

  

Answer:  Zero

Question: The virtual current of 4 A and 50 Hz flows in an ac circuit containing a coil. The power consumed in the coil is 240 W. If the virtual voltage across the coil is 100 V, then its resistance will be

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Different alternating voltages are given below. In which case the peak value and rms value are same?

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a) Only multiple strands for A.C, either for D.C.
• b) Only multiple strands for A.C, only single strand for D.C.
• c) Only single strand for D.C, either for A.C.
• d) Only single strand for A.C, either for D.C.

Answer: Only multiple strands for A.C, either for D.C.

Question: An AC source is rated 222 V, 60 Hz. The average voltage is calculated in a time interval of 16.67 ms. It

• a) Must be zero
• b) May be zero
• c) Is never zero
• d) None of these

Answer: Must be zero

Question: In India electricity is supplied for domestic use at 220 V. It is supplied at 110 V in USA. If the resistance of a 60 W bulb for use in India is R, the resistance of a 60 W bulb for use in USA will be

• a)

  

• b)

  

• c) 2R 
• d) R

Answer:

Question:

• a) 4 H
• b) 2 H
• c)

  

• d)

  

Answer: 4 H

Question: In a RLC circuit capacitance is changed from C to 2C. For the resonant frequency to remain unchanged, the inductance should be changed from L to

• a)

  

• b)

  

• c) 2 L
• d) 4 L

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d) V₀

Answer:

Question:

• a) 20 mA
• b) 10 mA
• c) 100 mA
• d) 200 mA

Answer: 20 mA

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d) 5

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a) 1
• b)

  

• c)

  

• d)

  

Answer: 1