1.

An air cored solenoid with length 20 cm area of cross section 20cm2. The current 2 A is suddenly switched off within 10^(-3) s. The average back emf induced across the ends of the open switch in the circuit is (ignore the variation in magnetic field near the ends of the solenoid)

Answer»

2 V
4 V
3 V
5 V

Solution :Here, `l=20cm=20xx10^(-3)m`,
`A=20cm^(2)=20xx10^(-4)m^(2)`
`N=400,I_(1)=2A,l_(2)=0,dt=10^(-3)s`
As `epsi=(dphi)/(dt)=(d(BAN))/(dt)`
`=(mu_(0)NdlAN)/(LDT)""(":. "B=(mu_(0)NI)/(l))`
`=(mu_(0)N(I_(1)-I_(2))AN)/(ldt)`
`=(4pixx10^(-7)xx(400)^(2)xx2xx20xx10^(-4))/(20xx10^(-2)xx10^-3)`


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