Free NEET Physics multiple-choice questions on Power in AC & Transformers. Attempt each question and reveal the answer with a full explanation.
A transformer is used to change 220 V to 11 V. If the primary has 800 turns, the number of turns in the secondary is: 40 400 80 20 In a transformer, the loss of energy due to the heating of the copper wires in the primary and secondary windings is called: Copper loss Iron loss Hysteresis loss Flux leakage In a transformer, the primary coil has 100 turns and the secondary coil has 200 turns. If the input power is 1000 W and the transformer is 90 % efficient, the output power is: 900 W 1000 W 1100 W 1800 W The primary of a transformer when connected to a DC battery of 10 V draws a current of 2 A. The secondary voltage will be: Zero 5 V 20 V 10 V A transformer has 500 turns in the primary and 1000 turns in the secondary winding. The primary coil is connected to a 200 V, 50 Hz AC supply. The output voltage and frequency at the secondary will be: 400 V, 50 Hz 100 V, 50 Hz 400 V, 100 Hz 200 V, 25 Hz In an AC circuit, the instantaneous voltage is V = 100 (100t) and current is I = 20 (100t + /2) . The average power dissipated in the circuit is: 0 W 1000 W 2000 W 500 W A step-down transformer transforms a supply line voltage of 2200 V into 220 V. The primary coil has 5000 turns. The efficiency and output power are 90 % and 8 kW respectively. The current in the primary is: 4.04 A 0.4 A 40 A 44 A 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, the efficiency of the transformer is approximately: 91 % 50 % 90 % 10 % A transformer has an efficiency of 80%. It works at 4 kW and 100 V. If the secondary voltage is 200 V, then the secondary current is: 16 A 20 A 25 A 10 A A transformer having efficiency of 90 % is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil respectively are: 450 V, 15 A 450 V, 13.5 A 600 V, 15 A 300 V, 15 A A transformer is used to light a 140 W, 24 V lamp from a 240 V AC mains. The current in the main cable is 0.7 A. The efficiency of the transformer is: 83.3 % 48 % 70 % 90 % A step-up transformer has a turn ratio of 1:20 . If a 1.5 V DC cell is connected across the primary, the voltage across the secondary will be: 0 V 30 V 0.075 V 1.5 V In an AC circuit, the instantaneous values of e.m.f. and current are e = 200 (314t) V and i = (314t + /3) A. The average power consumed is: 50 W 100 W 200 W 25 W A step-up transformer operates on a 230 V line and supplies current of 2 A to a load. The ratio of primary to secondary turns is 1 : 25 . Determine the primary current, assuming 100 % efficiency. 50 A 25 A 12.5 A 100 A A step-down transformer transforms 220 V to 11 V. If the primary current is 5 A and the efficiency is 90 % , the output current is: 90 A 100 A 110 A 81 A A step-up transformer has a turn ratio of 1:10 . A resistance of 1000 connected across the secondary appears to the primary as a resistance of: 10 100 1000 1 In an AC circuit, the instantaneous current is I = 5 (100t - /2) and the instantaneous voltage is V = 200 (100t) . The power consumed in the circuit is: 0 W 1000 W 500 W 250 W The average power dissipated in a series AC circuit containing R and L is given by: V rms I rms R/Z V rms I rms I rms 2 Z V rms 2 / R The primary of a transformer has 400 turns and the secondary has 2000 turns. If the power input is 12 kW at 220 V, what is the current in the secondary assuming 100 % efficiency? 10.9 A 54.5 A 2.2 A 25 A A transformer has 500 primary turns and 10 secondary turns. If the secondary is connected to a load of 10 , the effective resistance seen by the primary is: 25000 500 250 0.004 In an AC circuit, the instantaneous values of e.m.f. and current are e = E 0 t and i = I 0 ( t - /3) . The average power consumed is: E 0 I 0 / 4 E 0 I 0 / 2 3 E 0 I 0 / 4 Zero In an AC circuit, the instantaneous values of voltage and current are V = 100 (314t) and I = 2 (314t - /4) . The average power consumed is: 50 2 W 100 2 W 100 W 50 W Which of the following is not a source of energy loss in a transformer? Electrostatic shielding Eddy currents Hysteresis Flux leakage A transformer is used to change 240 V AC to 12 V AC. If the current in the primary is 0.5 A and the efficiency is 80 % , the current in the secondary is: 8.0 A 10.0 A 12.0 A 6.4 A Which of the following is true for an ideal step-up transformer? V s > V p and I s < I p V s > V p and I s > I p V s < V p and I s < I p V s = V p and I s = I p The primary and secondary coils of a transformer have N 1 and N 2 turns respectively. If the frequency of the input AC is f , the frequency of the output AC is: f f (N 2/N 1) f (N 1/N 2) f/2 A step-up transformer converts 100 V into 2500 V. If the number of turns in the primary is 100 , the number of turns in the secondary is: 2500 250 5000 100 A transformer works on the principle of: Mutual Induction Self Induction Eddy Currents Seebeck Effect In an AC circuit, the instantaneous current and emf are I = I 0 ( t - /2) and E = E 0 ( t) . The power dissipated in the circuit is: Zero E 0 I 0 2 E 0 I 0 2 E 0 I 0 The primary winding of a transformer has 100 turns and its secondary winding has 200 turns. The primary is connected to an AC supply of 120 V and the current flowing in it is 10 A. The voltage and current in the secondary are (assuming 100% efficiency): 240 V, 5 A 240 V, 20 A 60 V, 20 A 60 V, 5 A