The current in a solenoid of $$240$$ turns, having a length of $$12 cm$$ and a radius of $$2 cm$$, changes at a rate of $$0.8 A s^{-1}$$. Find the emf induced in it.
$$E=\cfrac { { \mu }_{ 0 }{ N }^{ 2 }A }{ l } \cfrac { dI }{ dt } =\cfrac { 4\pi \times { 10 }^{ -7 }\times { (240) }^{ 2 }\times \pi { (2\times { 10 }^{ -2 }) }^{ 2 } }{ 12\times { 10 }^{ -2 } } \times 0.8=6\times { 10 }^{ -4 }V$$
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A square current carrying loop is changed to a circular loop in time $$t_{1}$$. Then
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A copper wire having a resistance of $$0.01$$ ohm in each metre is used to wind a $$400$$ turn solenoid of radius $$1.0\ cm$$ and length $$20\ cm$$. Find the emf of a battery which when connected across the solenoid will cause a magnetic field of $$1.0 \times 10^{-2}$$ T near the centre of the solenoid.