Magnetic flux passing through a coil is initially 4 × 10 - 4 W b . It reduces to 10 % of its original value in t second. If the emf induced is 0.72 mV then t in second is

Step-by-step solution

ϕ 1 = 4 × 10 - 4   Wb ϕ 2 = 0 .1 × ϕ 1 = 4 × 10 - 5   Wb ε = 0.72   m V ∴     t = ? Using ε = - d ϕ d t ⇒ d t ⇒ d ϕ ε = 4 × 10 - 4 - 4 × 10 - 5 72 × 10 - 5 = 4 × 10 - 5 ( 9 ) 72 × 10 − 5 = 1 2 = 0.5    s