LC Ocillations given only one piece of data

[wrong_class]

Homework Statement

All the electric energy in a capacitor is converted to magnetic energy in 1.61 micro seconds. What is the period of oscillation?

Homework Equations

I assume Ue = q^2/2c, Ub = -.5 Li^2, w = 1/sqrt(LC) = 2 pi f

The Attempt at a Solution

I worked around the equations Ue = q^2/2c cos^2(w t + phi) and Ub = .5 Lw^2 q^2 sin^2(w t + phi) to get w t = pi/4, but the computer says that 1.288e-5 s is not the answer

 

[wrong_class]

anyone?

 

[ehild]

When the whole energy is in the capacitor, the energy in the inductor is zero, and vice versa. The energy is maximum in the inductor when the electric field is equal to the amplitude or the negative amplitude of E=A sin(wt). The same is true for the magnetic field in the inductor. Sketch the time dependence of both the electric field and the magnetic field. How many times during a period is the maximum electric energy converted to magnetic energy ?

 

[wrong_class]

2 times?

 

[ehild]

No. Draw a cosine function. It has maximum at t=0. When is the cosine equal to zero in terms of the period T?

ehild

 

[wrong_class]

T/4. so.. divide my answer by 4?

 

[ehild]

How does pi come in?

ehild

 

[wrong_class]

if the period is 2pi, then it would be at T = pi/2?

edit: forget it. it was a "N". my mistake