1. If the flux associated with a coil varies at the rate of 1 weber/min,the induced emf is

Transcription

1 1. f the flux associated with a coil varies at the rate of 1 weber/min,the induced emf is V 2. V V 4. Zero 2. Lenz s law is the consequence of the law of conservation of 1. Charge 2. Mass 3. Momentum 4. Energy 3. An induced emf is produced when a magnet is inserted into a coil. The magnitude of induced emf doesnot depend upon 1. The number of turns in the coil 2. The speed with which the magnet is moved 3. trength of the magnet 4. The resistivity of the wire of the coil 4. A magnet is placed along the axis of a circular coil. The magnet is moved away from the coil as shown in the figure. The induced current in the coil is 1. Zero 2. Clockwise 3. Anticlockwise 4. Cannot be estimated 5. A resistance coil is held horizontally and a magnet is allowed to fall vertically.then the acceleration of the magnet as it approaches the coil is 1. Equal to g 2. Less than g 3. More than g 4. ometimes less and sometimes more than g 6. A current from A to B is increasing in magnitude. The direction of induced current in the loop is 1. Clockwise 2. Anticlockwise 3. o current induced in the loops 4. First clockwise and then anticlockwise A B

2 7. An electron moves along the line AB which lies in the plane as a circular loop of conducting wire as shown in the diagram. The direction of current induced in the loop as the electron approaches the loop is 1. o current will be induced 2. The current will be clockwise A 3. The current will be anticlockwise 4. The current will change the direction as the electron passes by B 8. n the figure the coil and the magnet are moved in the same direction with the same speed v. The induced emf is 1. Zero 2. Proportional to v 3. Proportional to v Doesnot depend on v v 9. A cylindrical magnet is placed is near circular coil. The magnet is rotated about tis own is as shown in the figure. The induced current in the coil 1. Zero 2. n anti-clockwise 3. n clock-wise direction 4. Directly proportional to the speed of rotation 10. A straight conductor of length 4m moves at a speed of 10m/s when the conductor makes an angle of 30 0 with the direction of magnetic field of 0.1weber/m 2. The induced emf is 1. 1V 2.2V 3. 4V 4. 8V 11. A copper rod moves parallel to the horizontal direction. The induced emf across its ends due to earth s magnetic field will be maximum at 1. Equator 2. Latitude Latitude Poles 12. The induced emf in a conductor moving through a uniform magnetic field doesnot depend on its 1. Velocity 2. Length 3. Diameter 4. Orientation 13. The self-induced emf in a 0.2H coil when the current is changing at the rate of 400ampere/sec is V 2. 80V 3. 8x10-4 V 4. 8x10-5 V

3 14. f a current of 3amperes flowing through the primary coil is reduced to zero in 0.01sec then the induced emf in the secondary coil is 1500V. The mutual inductance between the coil is H 2. 5H H 4. 10H 15. Two circular coils can be arranged in any of the three situations as shown in the figure. Their mutual inductance will be 1. Maximum in case A 2. Maximum in case B 3. Maximum in case C 4. ame in all cases A B C 16. Workdone by a battery to establish a current of 5A in an inductor coil of inductance L=0.04H is J J J 4. 20J 17. n an induction coil the emf induced in the secondary is maximum 1. Either at the make or break of the primary circuit 2. either at the make or break of the primary circuit 3. At the make of primary circuit 4. At the break of primary circuit 18. A rectangular coil ABCD is rotated with uniform angular velocity about the axis of the coil perpendicular to uniform magnetic field. The induced emf of the coil would be maximum when 1. The plane of the coil is vertical 2. The plane of the coil makes an angle of 45 0 with the magnetic field 3. The plane of the coil is parallel to the magnetic field 4. The plane of the coil makes an angle of 30 0 with the magnetic field 19. The instantaneous current in a circuit is = 2 sin ( ω t + φ ). The rms value of current in ampere is An inductive circuit has zero resistance.when a AC voltage is applied across the circuit the current lags behind the applied AC voltage by an angle

4 21. Relation between the mean value and rms value of a AC is 2 2 = π 1. rms m 2 2 = π 4. m rms 2. m rms = 3. rms m 22. Which of the following phenomenon is helpful in the working of a choke coil 1. elf induction 2. Mutual induction 3. Eddy current 4. All of thes 23. A coil has a resistance of 8Ω and inductive reactance 6Ω. The impedance of the coil is 1. 8Ω 2. 6Ω 3. 14Ω 4. 10Ω 24. Power factor of AC circuit varies between 1. 0 to to to to An alternating voltage is connected in series with a resistance R and an inductance L. f the potential drop across the resistance is 200V and across inductance is 150V the applied voltage is V V V V 26. A resistor, capacitor and an inductor are connected in series with a AC source. Which of the following statement is true? The current in the resistor lags behind 1. Current in the capacitor 2. Current in the inductor 3. Voltage across capacitor 4. Voltage across inductor 27. The phase difference between current and voltage at resonance is 1. Zero 2. π/2 3. π 4. π 2 = A step down transformer is used to reduce the voltage from 110V to 11V. The current in the primary and secondary are 2A and 18A. The efficiency of the transformer is % 2. 90% 3. 80% 4. 60%

5 29. A transformer is used 1. To convert alternating current to direct current 2. To convert direct current to alternating current 3. To convert mechanical energy into electrical energy 4. To transform alternating current and voltage 30. To minimize eddy current loss in the core of a transformer 1. We should increase the number of turns in the secondary coil 2. We should use laminated core 3. We should use a step down transformer 4. We should use a weak alternating current at high potential 31. A copper disc of radius 0.1m is rotated about its centre with 20 rev/s in a uniform magnetic field of 0.2T with its plane perpendicular to the field. The emf induced across the radius of disc is 1. π/10 V 2. 2 π/10 V 3. 4 πx10-2 V 4. 2πX10-2 V 32. The value of current through a coil of inductance one henry and of negligible resistance when connected through an AC source of 200 V and 50 Hz is (1) A (2) A (3) A (4) 4 A 33. Power factor of LCR series circuit is maximum when (1) R=0 (2) X L = 0 (3) X L = X C (4) X C = n an AC circuit a resistance R Ω is connected in series with an inductance L. f the phase angle between voltage and current is 45 0, the value of inductive reactance is (1) R 4 (2) R 2 (3) R (4) zero 35. With usual notations the energy dissipated in an ideal inductor is given by (1) L (2) ½ L (3) ½ L 2 (4) zero

6 36. A capacitor of capacitance C has inductance X. f capacitance and frequency becomes double, then reactance will be (1) 4X (2) X 2 (3) X 4 (4) 2X 37. nduction furnace is based on (1) elf induction (2) Mutual nduction (3) Eddy Currents (4) one of these An alternating voltage V = sin(100t) volt is connected to a 1µF capacitor through an AC ammeter. The reading of the ammeter is (1) 10 ma (2) 20mA (3) 40 ma (4) 80 ma 39.Powerloss in an ac circuit will be minimum when the circuit has (1) high resistance and high inductance (2) high resistance and low inductance (3) low resistance and low inductance (4) low resistance and high inductance 40.f L and R denote inductance and resistance respectively then the dimension of L/R is (1) M 0 L 0 T 0 (2) M 0 L 0 T (3) M 2 L 0 T 2 (4) MLT 2