The flux linked with a coil at any instant t is given by ϕ=10t2−50t+250. The induced e.m.f. at t = 3 sec is :

ϕ=10t2−50t+250 Induced em,mf=−dϕdt=−ddt10t2−50t+250=−(20t−50)The induced e.m.f. at t = 3 sece=−(20×3−50)=−(60−50)=−10V