A long solenoid having $$200$$ turns per cm caries a current of $$1.5$$ amp. At the centre of it is placed a coil of $$100$$ turns of $$cross-sectional$$ area $$3.14$$ x $$10-4$$ $$m2$$ having its axis parallel to the field produced by the solenoid. When the direction of current in the solenoid is reversed within $$0.05$$ $$sec$$., the induced e.m.f. in the coil is

Question

Infinity Learn · Accepted Answer

$$B=$$μ$$0ni=4$$π×$$10$$−$$7200$$×$$10$$−$$2$$×$$1$$⋅$$5=3$$⋅$$8$$×$$10$$−$$2Wb/m2Magnetic$$ flux through each turn of the coilΦ$$=BA=3$$⋅$$8$$×$$10$$−$$23$$⋅$$14$$×$$10$$−$$4=1$$⋅$$2$$×$$10$$−$$5$$ webreWhen the current in the solenoid is reversed, the change in magnetic $$flux=2$$×$$1$$⋅$$2$$×$$10$$−$$5=2$$⋅$$4$$×$$10$$−$$5$$ weberInduced e.m.f.$$=Nd$$Φ$$dt=100$$×$$2$$⋅$$4$$×$$10$$−$$50$$⋅$$05=0$$⋅$$048V$$

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