A coil of mean area 500 cm2 and having 1000 turns is held perpendicular to a uniform field of 0.4 gauss. the coil is turned through 180o in 1/10 second. The average induced emf (in V) is

When the plane of coil is perpendicular to field, the angle between area A→ and field B→ is 0o.The flux linked with coil ϕ1=NBAcos00=NBA. when the coil rotates 1800 flux linked φ2=BANcos1800=-BAN∴ Change in flux ϕ=ϕ2−ϕ1=−2NBA The magnitude of the induced emf is ε=−dϕdt=2NBAdt=2×1000×0.4×10-4×500×10-4110=0.04V