Q. 25

# (a) State Faraday

Answer :

(a) Faraday’s first law: It states that whenever a conductor is placed in a varying magnetic field, emf is induced in the conductor.

Faraday’s second law: It states that the induced emf is equal to the rate of change of flux.

(b) Consider a bar magnet and a loop. Now, when the bar magnet is moved towards the loop, it will observe a repulsive force due to the current induced in the loop. Hence, the mechanical work done in moving the magnet will be equal to the Joule’s heat dissipated by the current carrying loop. Therefore, law of conservation of energy is preserved.

(c) According to Lorentz law, At equilibrium, Fnet = 0    when velocity is perpendicular to magnetic field, θ=90    OR

Phasor diagram: V makes an angle ωt1 with x axis and current I lags behind the voltage by π/2.  Graph showing variation of applied voltage(v) and current(i) as a function of ωt: Power dissipated in the circuit = v × i

= (vm sin ωt)[im sin(ωt+φ)]

= vmim [ cosφ - cos(2ωt+φ) ]

Average power =  Pav = Veff Ieff cosφ

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