18%20-%20Electromagnetic%20Induction%20and%20Alternating%20Currents

# 18%20-%20Electromagnetic%20Induction%20and%20Alternating%20Currents

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18 - ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENTS ( Answers at the end of all questions ) Page 1 1 ) The self inductance of the motor of an electric fan is 10 H. In order to impart maximum power at 50 Hz, it should be connected to a capacitance of ( a ) 8 µ F ( b ) 4 µ F ( c ) 2 µ F ( d ) 1 µ F [ AIEEE 2005 ] 2 ) The phase difference between the alternating current and emf is π / 2. Which of the following cannot be the constituent of the circuit ? ( a ) R, L ( b ) C alone ( c ) L alone ( d ) L, C [ AIEEE 2005 ] 3 ) A circuit has a resistance of 12 ohm and an impedance of 15 ohm. The power factor of the circuit will be ( a ) 0.4 ( b ) 0.8 ( c ) 0.125 ( d ) 1.25 [ AIEEE 2005 ] 4 ) A coil of inductance 300 mH and resistance 2 is connected to a source of voltage 2 V. The current reaches half of its steady state value in ( a ) 0.1 s ( b ) 0.05 s ( c ) 0.3 s ( d ) 0.15 s [ AIEEE 2005 ] 5 ) In an LCR series a.c. circuit, the voltage across each of the components, L, C and R is 50 V. The voltage across the LC combination will be ( a ) 50 V ( b ) 50 2 V ( c ) 100 V ( d ) 0 V ( zero ) [ AIEEE 2004 ] 6 ) A coil having n turns and resistance having R is connected with a galvanometer of resistance 4R . This combination is moved in time t seconds from a magnetic field W 1 weber to W 2 weber. The combined current in the circuit is ( a ) 5Rnt W W 1 2 - ( b ) - 5Rt ) W W ( n 1 2 - ( c ) Rnt W W 1 2 - - ( d ) Rt ) W W ( n 1 2 - - [ AIEEE 2004 ] 7 ) In a uniform magnetic field of induction B, a wire in the form of semicircle of radius r rotates about the diameter of the circle with angular frequency ω . The axis of rotation is perpendicular to the field. If the total resistance of the circuit is R, the mean power generated per period of rotation is ( a ) 2R r B 2 ω π ( b ) 8R ) r B ( 2 2 ω π ( c ) 2R ) r B ( 2 ω π ( d ) 8R ) r B ( 2 2 ω π [ AIEEE 2004 ] 8 ) In an LCR circuit, capacitance is changed from C to 2C. For the resonant frequency to remain unchanged, the inductance should be changed from L to ( a ) 4 L ( b ) 2 L ( c ) L / 2 ( d ) L / 4 [ AIEEE 2004 ] 9 ) A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 radians per second. If the horizontal component of earth’s magnetic field is 0.2 × 10 - 4 T, then the emf developed between the two ends of the conductor is ( a ) 5 µ V ( b ) 50 µ V ( c ) 5 mV ( d ) 50 mV [ AIEEE 2004 ] 10 ) The magnetic flux linked with a coil is given by the equation φ = 3t 2 + 4t + 9 Wb. The magnitude of induced emf at t = 2 sec. is ( a ) 16 V ( b ) 9 V ( c ) 4 V ( d ) 1 V [ AIEEE 2003 ] 11 ) When the current changes from + 2 A to - 2 A in 0.05 second, an e.m.f. of 8 V is induced in a coil. The coefficient of self-induction in the coil is ( a ) 0.1 H ( b ) 0.2 H ( c ) 0.4 H ( d ) 0.8 H [ AIEEE 2003 ]

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18 - ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENTS ( Answers at the end of all questions ) Page 2 12 ) Two coils are placed close to each other. The mutual
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18%20-%20Electromagnetic%20Induction%20and%20Alternating%20Currents

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