JEE Physics Alternating Current MCQs Set B

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: A

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: A

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: A

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: 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) Zero
(c) 100 V
(d) 220 V

Answer: A

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: A

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: A