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Electric Charges And Fields

Question
CBSEENPH12037852

A long solenoid with 15 turns per cm has a small loop of area 2.0 cm2 placed inside normal to its axis. If the current carried by the solenoid changes steadily from 2.0 A to 4.0A in 0.1 s, what is the induced emf in the loop while the current is changing?

Solution
Given, a solenoid.
Number of turns per unit length,n = 15 turns/cm = 1500 turns/m
Area of the small loop, A = 2 cm
2 = 2 x 10–4 m2
Initial current, I1 = 2A
Final current, I
2 = 4A
Δt = 0.1s

The magnetic field associated with current I1,
                     B1 = μ0 n I1 

The magnetic field associated with current I2,
                     B2 = μ0 n I2 

The change in flux assosciated with change in current in solenoid, 

ϕ = (B2-B1) A         = 4π×10-7×1500 × (4-2) × 2 × 10-4
     = 7.6 × 10-7 weber

The induced EMF while current is changing,   
                 E = ϕt       = 7.6 × 10-70.1      = 7.6 × 10-6V