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

Question

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

Infinity Learn · Accepted Answer

$$B=$$μ$$0$$ n $$i=(4$$π×$$10$$−$$7)(200$$×$$10$$−$$2)$$×$$1.5$$ $$=3.8$$×$$10$$−$$2Wb/m2$$ϕ$$=BA=3.8$$×$$10-2$$×$$3.14$$×$$10-4=1.2$$×$$10-5wbMagnetic$$ flux current in the solenoid is reversed, the change in magnetic $$flux=2$$×$$(1.2$$×$$10$$−$$5)=2.4$$×$$10$$−$$5weberInduced$$ e.m.f.$$=Ndodt=100$$×$$2.4$$×$$10$$−$$50.05=0.048V$$

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