Pls do this

Solution:
Magnetic energy is maximum when the electrical energy is zero. hence, t=T/4,3T/4,5T/4,..

At t = T/4 energy stored is completely magnetic

 

$$\begin{gathered} Time t = T/4 = (2\pi \surd LC)/4 \\ = (\pi \surd 20 \times {10}^{-3} \times 50 \times {10}^{-6})/2 \\ = (\pi \surd {10}^{-6})/2 = \left({10}^3\pi \right)/2 = 500 \times 3.14 \\ = 1.57 ms \end{gathered}$$