1. A capacitor of 2 $\mu$F draws a current of 4 mA when connected across an a.c. of 300 Hz. The voltage drop across capacitor is

2. The device that does not work on the principle of mutual induction is

3. A 750 Hz, 20 volt source is connected to a resistance of 100 ohm, an inductance of 0.1803 H and a capacitance of 10$\mu$F, all in series. The time in which the resistance (thermal capacity = 2 Joule${/}^{o}C$) will get heated by ${10}^o$C is

4. A resistor, an inductor and a capacitor are connected in series to an a.c. power supply. When measured with the help of an a.c. voltmeter, the voltage across them are found to be 80 V, 30 V and 90 V respectively. What is the supply voltage ?

5. A coil has 2000 turns and area of 70${\mathrm{cm}}^2$. The magnetic field perpendicular to the plane of the coil is 0.3 wb/$m^2$ and takes 0.1 sec to rotate through ${180}^o$. The value of induced e.m.f. will be

6. An alternatinf current source of frequency 100 Hz is joined to a combination of a resistance, a capacitance and a coil in series. The potential difference across the coil, the reistance and the capacitor is 46, 8 and 40 volt, respectively. The electomotive force of alternating current source in volt is

7. A dynamo works on the principle of

8. A certain choke coil of negligible resistance draws a current of 8 A, when connected to a supply of 100 volts, at 50 Hz. A certain non- inductive resistance, under the same conditions carries a current of 10 amp. If the two are transferred to a supply system working at 150 volts, at 40 Hz, the total current they will take if joined in series is

9. In an A.C. circuit the potential V and the current I are given respectively by
V = 100 sin (100t) volt
and I = 100 sin (100t + $\pi$/3) milliampere
The power dissipation in the circuit will be

10. In a step down transformer the turns ratio is 3 : 1. A cell of e.m.f. 1.5 volt is connected across the primary. The coltage across secondary is

11. In a region of uniform magnetic induction B = ${10}^{-2}$tesla, a circular coil of radius 30 cm and resistnace ${\pi }^2$ ohm is rotated about an axis which is perpendicular to the direction of B and which forms a diameter of the coil. If the coil rotates at 200 r.p.m. the amplitude of the alternating current induced in the coil

12. The power factor of a pure resistive and pure inductive circuit have a ratio of

13. In a step-up transformer the turn ration is 1 : 2 A leclanche cell (e.m.f. = 1.5 V) is connected across the primary. The voltage developed in the secondary would be

14. In an A.C. circuit, the instantaneous values of e.m.f. and current are E = 200 sin 314t volts and I = sin (314t+$\pi$/3) amphere. The average power consumed in watts is

15. A wire of fixed length l can be formed into many circular loops of varying radii r depending on the number of turns n. The loop so formed is carrying a current and is placed normally in a uniform magnetic field B. In order that the torque on the circular loop formed be maximum; the number of turns n must equal

16. When current changes from +2 A to $-$2A in 0.05 sec an emf of 8 V is induced in a coil. The coefficient of self inductance of the coil is

17. An alternating emf, E (in volt) = 200 $\sqrt{2}$ sin 100 t is connected to 1$\mu$F capacitor through an a.c. ammeter. The current in the ammeter is

18. Two inductors each of inductance L are connected in series with opposite magnetic flux. What is the resultant inductance?

19. In an a.c circuit current and voltage are given by
I = 100 sin $(314t+\frac{\pi }{3})$
E = 100 sin 314 t volt.
The power dissipated in the circuit is

20. The instantaneous current and voltage in an a.c. circuit is given by
I = 4 sin $\omega t$
E = 150 cos $[\omega t+\frac{\pi }{3}]$
respectively. then the phase difference between voltage and current in the circuit is given by

21. A 50 Hz a.c current of crest value 1 A flows through the primary of transformer. If the mutual inductance between the primary and secondary be 1.5 H. The crest voltage induced in the secondary is

22. A copper disc of radius 0.1 m rotated about its centre with 10 revolutions per sec. in a uniform magnetic field of 0.1 Tesla with its plane perpendicular to the field. The emf induced between the centre and the circular edge of the disc

23. A current from A to B is increasing in magnitude. What is the direction of induced current in the loop?

24. If the number of turns in the coil and length doubled then coefficient of self induction of the coil

25. If N is the number of turns in a coil the value of self inductance varies as

26. An inductor may store energy in

27. The back emf in a DC motor is maximum when

28. The total charge induced in a conducting loop when it is moved in a magnetic field depends upon

29. Two different coils have self inductance 8mH and 2mH. The current in both coils are increased at the same constant rate. The ratio of the induced emfs in the coils is

30. The magnetic flux linked with a loop placed with its plane perpendicular to the magnetic field is given by $\phi ={6t}^2+7t+1$ where $\phi$ is in milli weber. How much emf will be induced at t =2seconds

31. A car fitted with a long vertical antenna moves along a horizontal road. The induced emf across the antenna is maximum when it moves along

32. A coil of resistance 5$\mathrm{\Omega }$ and inductance 4H is connected to a 10V battery. The energy stored in the coil

33. Which one of the following graphs represents growth of current i with time i in an LR circuit

a)
b)
c)
d)

34. L, C, R represent the physical quatities inductance, capacitance and resistance. The combination which has the dimensions of frequency is

35. Two coils of self inductance $L_1$and $L_2$ are placed close together so that effective flux in one coil is completely linked with the other. IfM is the mutual inductance between them, then

36. A coil of wire is held with its plane horizontal. A small bar magnet is dropped vertically down through it. The magnet experiences

37. An all metal aeroplane dives down vertically at 300 km/h at a place when the horizontal intensity of the earth magnetic field is ${0.4\times 10}^{-4}T$. If the wing span is 30m the induced emf between the tips of the wings is

38. The energy of self inductance L carrying a current i resides in

39. The energy required to establish a current of 4A in an inductance 200mH is

40. A staight conductor of length 0.4m is moved with a speed of 0.7 m/s perpendicular to a magnetic field of intensity 0.9 T. Induced emf across the conductor is

41. The direction of the induced emf is given by

42. The instrument which works on the principle of mutual induction is

43. A charged particle experiences the maximum force when

44. What is the self inductance of a coil in which an induced emf of 2V is self up when the current is changed at the rate of 4${\mathrm{As}}^{-1}$.

45. A coil having number of turns N and area A is rotated in a uniform magnetic field B with angular velocity $\omega$. The maximum emf induced in the coil

46. A uniform metal rod of length l is moved with a velocity v parallel to the magnetic field B. The emf induced across its ends

47. Lenz's law is a consequence of law of conservation of

48. The law of elecro magnetic induction has been used in the construction of

49. A wire moves across a magnetic field. The emf induced across the wire depends on

50. When a fluresent tube is used in an ac circuit a