Question

An LC circuit contains a 20 mH inductor and a 50 .$\mu$ F capacitor with an initial charge of 10 mC. The resistance of the circuit is.negligible. Let the instant at which the circuit which is closed be t = 0. At what time the energy stored is completely magnetic?

• A. t = 0
• B. t = 1.54 ms
• C. t = 3.14 ms
• D. t = 6.28 ms

Answer 1

Answer: (B)

t = 1.54 ms

At time $t=\frac{T}{4},$ energy stored is completely mangnetic.

$\therefore Timet=\frac{T}{4}=\frac{2\pi \sqrt{LC}}{4}\Rightarrow t=\frac{\pi \sqrt{20\times {10}^{-3}\times 50\times {10}^{-6}}}{2}$

$t=\frac{\pi \sqrt{1000\times {10}^{-9}}}{2}=\frac{\pi \sqrt{1\times {10}^{-6}}}{2}=1.57ms$