# energy related simple problem

#### fl415

Joined Sep 7, 2011
4

Part a
Using the power versus t plot for 0<=t<=10s calculate the energy delivered to the circuit element at t=1 s .
Part b
Calculate the energy delivered to the circuit element at t=6 s
part c
Calculate the energy delivered to the circuit element at t=10s .

can anyone help me??
thank you very much!!!

#### t_n_k

Joined Mar 6, 2009
5,455
The question is firstly asking you to plot the instantaneous power function p(t)=i(t) x v(t). In other words plot i(t) [the top graph] multiplied by v(t) [the bottom graph] for t=0 to 10 seconds.

The energy W(tx) delivered at any time 'tx' is the summation of the area under the p(t) curve from t=0 to tx seconds. Having plotted the instantaneous power curve you should then be able to plot the energy curve by adding up the areas under p(t). This may involve some simple integration.

#### fl415

Joined Sep 7, 2011
4
How do I multiple two graph? Sorry about I ask a stupid question

#### t_n_k

Joined Mar 6, 2009
5,455
Look at the two graphs. Select several time values and multiply the i(t) and v(t) values at those times to give a p(t) value at that time. Plot those p(t) values against a time scale corresponding to the i(t) and v(t) time axes. Take some care when the v(t) function values switch instantaneously at certain times (1sec, 3sec, 5sec and 7sec). A clear picture should emerge after a few values are calculated.

At t=0 sec i(0)=0 and v(0)=5 so p(0)=i(0)*v(0)=0

At t=0.5 sec i(0.5)=10 and v(0.5)=5 so p(0.5)=i(0.5)*v(0.5)=50

At t=1 sec i(1)=20 and v(1)=(5) so p(1)=i(1)*v(1)=100

For t>1 sec but less than 3sec v(t) =0 so p(t) in that range is also zero.

And so it goes on.