How much of this energy is stored in the magnetic field of the inductor?

mr_coffee

For the circuit of Figure 30-19, assume that EMF= 14.0 V, R = 5.40 , and L = 5.00 H. The battery is connected at time t = 0.
Picture:
http://www.webassign.net/hrw/hrw7_30-19.gif
Okay i know there is a simple formula to find the:
(a) How much energy is delivered by the battery during the first 2.00 s?
J

but i don't know where it is, anyone know it?

Also I tried part (b) and got it wrong for some reason:
How much of this energy is stored in the magnetic field of the inductor?
wrong check mark J

I used:
V = iR.
Ub = .5L*i^2;
i = 14/5.40 = 2.59 Amps
Ub = .5*5.00*2.59^2 = 16.77 but they didn't like that at all, any ideas?
thanks.

ranger

When you analyze a L/R circuit, follow these simple rules:

To analyze an RC or L/R circuit, follow these steps:
(1): Determine the time constant for the circuit (RC or L/R).
(2): Identify the quantity to be calculated (whatever quantity whose change is directly opposed by the reactive component. For capacitors this is voltage; for inductors this is current).
(3): Determine the starting and final values for that quantity.
(4): Plug all these values (Final, Start, time, time constant) into the universal time constant formula and solve for change in quantity.
(5): If the starting value was zero, then the actual value at the specified time is equal to the calculated change given by the universal formula. If not, add the change to the starting value to find out where you're at.

You can refer to here for more info.
http://www.ibiblio.org/obp/electricC.../DC/DC_16.html

mr_coffee

Ahhh thanks for the help, i'm all done now with electricity and magnetsim, w00t! I got an A in the class, thanks everyone!

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mr_coffee	Ahhh thanks for the help, i'm all done now with electricity and magnetsim, w00t! I got an A in the class, thanks everyone!