Page 1 :
TEJAS ACADEMY OF SCIENCE, , , , , , , , , , , , Physics, Time : 1.00 hr xi Marks : 20, Electromagnetic Inductions |, 1) What is the dimensional formula for the coefficient of self induction ?, A) (U) = IM'L?T-*) B) (L] = IM'V7T-3A"], C) [LJ = (M'1L2T 2A 2 D) [L] = (M°L'T 7A 3), , 2) Two coils have a mutual inductance of 5 x10 -° H. The current changes in the first coil according to, the equation, |; = Ip sinwt where Ip = 10A and w = 100 rad/s. What is the value of the maximum, e.m-f. in the second coil ?, , A)2nV B)3nv Ch4nv D) Sav, , 3) Two circular coils can be kept in any of the three arrangements as shown in the figure. Their mutual, inductance will be, , Ss 0, Ooo, , (A) (B) «), A) Maximum in arrangement (C) B) Maximum in arrangement (A), C) The same in all arrangement D) Maximum in arrangement (B), , 4) The linear momentum in mechanics is expressed as m « v. What is the analogous expression in, electricity?, , A)L«@ B)txV cj1xa pu, , 5) Acurrent inacoil changes from 2A to 2 Ain 0.05 second. If the induced e.m-f. is 8V, then the, self-inductance of the coil is, , A)O.1H B) 15H C)2H D)2.2H, , 6) Two co-axial solenoids are made by winding thin insulated wire over a pipe of cross-sectional area A =, 10 c m® and length = 20 cm. If one of the solenoids has 300 turns and the other has 400 turns, then, their mutual inductance is [take uo = 4m « 10-7 TmA~1], , A) 4.8 x 10-5H. B) 4.8x x 10-4H C) 2.4m x 10-5H D) 2.40 x 10-4H, 7) If His the number of turns in a circular coil, the value of Its self-inductance varies as, , A)N? B)N ? c) N* D)N', 8) A-solenoid has 2000 turns wound over a length of 0.30 metre. The area of its cross-section is 1.2, , «10-5? . Around its central section, a coil of300 turns is wound. If an initial current of 2 A in the, solenoid is reversed in 0.25 sec, then the e.m-f. induced in the coil is, , A) 48 mV B) 68 mV C) 20 mV D) 8 mv

Page 2 :
TEJAS ACADEMY OF SCIENCE 2, , , , 9) Which one of the following units denotes the dimensions ML” /Q* , where Q denotes the electric, charge ?, , A) Hm? B) Weber (Wb) C) Wb! m? D) Henry (H), , 10) In a step up transformer, the input voltage is 300 V and the output voltage Is 15 KV. Then the ratio of, the number of turns in the primary to that in the secondary is, , A)1:20 B)1:30 c)1:40 D)1:50, , 11) The primary and secondary voltages of an ideal step down transformer are 200 V and 25 V, respectively. The secondary is connected to a device, which draws a current of 2A. What is the current, in the primary?, , A) 100 mA B) 150 mA C) 200 mA D) 250 mA, , 12) A step down transformer works on 220 volts a.c. mains. It is used to light a 100 W, 20 V bulb. The main, current is 0.5 A. What is the efficiency of the transformer ?, , A)91% B) 80% C)71% D) 51%, , 13) A transformer has 100 turns in the primary and 500 turns in the secondary. If the primary is connected, to 220 V DC supply, then the voltage developed across the secondary will be, , A) 2200 V B) 1100 V C) Zero D)44V, , 14) A step down transformer has a turn ratio of 20 : 1. If 8 volts are developed across 0.4 () secondary,, then the primary current will be, , AVIA B)2A Ch4aa D)O5A, , 15) A step down transformer has a turn ratio of 5: 1. It is connected to 220 V, 50 Hz a.c. mains supply. The, secondary voltage and the frequency of secondary voltage are given by, , A) 44 V, 10 Hz B) 110 V, 50 Hz C) 44 V, 50 Hz D) 1100 V, 10 Hz, , 16) A transformer has 230 volts applied to the primary and gives 4.6 V in the secondary. The secondary is, connected to a load which draws a current of 5 A. The current in the primary Is, , A)IA B)O1A Ch2A D)10A, , 17) The primary winding of a transformer has 50 turns while its secondary has 500 turns. If the primary is, connected to an a.c. supply of 220 V, 50 Hz, then the output at the secondary will be, , A) 220 V, 50 Hz B) 2200 V, 50 Hz C) 2200 V, 500 Hz D) 22 V, 5 Hz, , 18) A transformer is used to reduce the mains supply of 220V to 22V. If the currents in the primary and, secondary are 2A and 15A respectively, then the efficiency of the transformer Is, , A) 65 % B) 75% C) 80 % D) 90%, , 19) The number of turns in the primary and secondary coils of a transformer are 200 and 800 respectively., It the voltage developed across the secondary Is 240 V, then the potential difference across each turn, of the primary will be, , , , Rahul Chavan Sir 9130013007

Page 3 :
TEJAS ACADEMY OF SCIENCE, , , , A) 0.1 Viturn B) 0.2 V/turn C) 0.3 Viturn D) 0.5 Viturn, , 20) tn an Ideal step down transformer, the input voltage Is 400 V and the output voltage Is 20 V. The output, voltage is used to operate a device, having an impedance of 100 ohms. What is the current in the, primary circuit?, , A)10mA B) 20 mA c)5mA D)1mA, , , , Rahul Chavan Sir 9130013007