A coil having inductance 2.0 H and resistance `20 Omega` is connected to a battery of emf 4.0 V. Find (a) the current a the instant 0.20 s after the connection Is made and (b) the magnetic energy at this instant.

Options

A. 0.45 A, 0.3 J
B. 0.6 A, 5 J
C. 0.17 A, 0.03 J
D. 0.1 A, 0.3 J

Answer

C

Explanation

`I=I_(0) (1-e^(-Rt//2))`
`I_(0)=(4.0)/(20)=0.2A`
` I=0.2 (1-e^(-(20xx0.2)/(2)))`
`I=0.17A`
`E_(B)=(1)/(2)LI^(2)=0.02J`