20 s
100 s
10 s
50 s
Correct option is B. 20 s
A = A_0 e^-γ t
A = A_0/2 after 10 oscillations
∵ After 2 seconds
A_0/2 = A_0 e^-γ (2)
2 = e^2 γ
ln 2 = 2 γ
γ = ln 2/2
∵ A = A_0 e^-γ t
ln A_0/A = γ t
ln 1000 = ln 2/2 t
2 (3 ln 10/ln2) = t
6 ln 10/ln 2 = t
t = 19.931 sec ≈ 20 sec