In the circuit of figure, the switch is closed to position-1 for a long time. At t = 0 the switch position is changed from postion-1 to postion-2. Find an expression for the current i(t).

• A. i(t) = (E/R) sin√(LC) t A
• B. i(t) = (E/R) sin[1/√(LC)]t A
• C. i(t) = (E/R) cos√(LC) t A
• D. i(t) = (E/R) cos[1/√(LC)]t A

Answer: (D)

Standard eqution of current for this condition,
i(t) = i(0+)*cos(wt)
i(0+) = E/R
For LC circuit,
w = 1/√(LC)

i(t) = (E/R)*cos((1/√(LC))*t) A