JEE Physics Alternating Current MCQs Set A

Question. Hot wire ammeters are used for measuring
(a) Both AC and DC
(b) Only AC
(c) Only DC
(d) Neither AC nor DC

Answer: A

Question. In alternating current circuits, the a.c. meters measure
(a) r.m.s. value
(b) Peak value
(c) Mean value
(d) Mean square value

Answer: A

Question. A 110 V d.c. heater is used on an a.c. source, such that the heat produced is same as it produces when connected to 110 V dc in same time-intervals. What would be the r.m.s. value of the alternating voltage?
(a) 110 V
(b) 220 V
(c) 330 V
(d) 440 V

Answer: A

Question. The time required for a 50 Hz sinusoidal alternating current to change its value from zero to the r.m.s. value
(a) 2.5 × 10^–3 s
(b) 10^–1 s
(c) 10^–6 s
(d) 1.5 × 10^–2 s

Answer: A

Question. An inductive circuit contains a resistance of 10 ohms and an inductance of 2 henry. If an alternating voltage of 120 V and frequency 60 Hz is applied to this circuit, the current in the circuit would be nearly
(a) 0.16 A
(b) 0.48 A
(c) 0.80 A
(d) 0.32 A

Answer: A

Question. A coil and a bulb are connected in series with a 12 volt direct current source. A soft iron core is now inserted in the coil. Then
(a) The intensity of the bulb remains the same
(b) The intensity of the bulb increases
(c) The intensity of the bulb decreases
(d) Nothing can be said

Answer: A

Question. When 100 volt d.c. is applied across a solenoid, a current of 1.0 A flows in it. When 100 volt a.c. is applied across the same coil, the current drops to 0.5 A. If the frequency of a.c. source is 50 Hz the impedance and inductance of the solenoid is
(a) 200 ohm and 0.55 henry
(b) 100 ohm and 0.86 henry
(c) 200 ohm and 1.0 henry
(d) 100 ohm and 0.93 henry

Answer: A

Question. With increase in frequency of an a.c. supply, the impedance of an LCR series circuit
(a) Decreases at first, becomes minimum and then increases
(b) Increases
(c) Decreases
(d) Remains constant

Answer: C

Question. Mark the incorrect statemen
(a) The use of a capacitor is avoided in the circuit of an induction coil
(b) Power factor can often be improved by the use of a capacitor of appropriate capacitance in the circuit
(c) For circuits used for transporting electric power, a low power factor implies large power loss in transmission
(d) In any AC circuit, the applied instantaneous voltage equals to the algebraic sum of the instantaneous voltages across the series elements of the circuit.

Answer: A

Question. Power factor of an ideal choke coil (i.e., R = 0) is
(a) Zero
(b) Near about zero
(c) Near about one
(d) One

Answer: A

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) 0 V
(c) 100 V
(d) 220 V

Answer: B