# Homework Help: Electrical Engineering - Energy Graph Question

1. Sep 13, 2010

### Larrytsai

1. The problem statement, all variables and given/known data
Question number 3!, I attached it. Need help!

Figure 1 shows the current through and the voltage across a device. Find the total energy absorbed by the device fore the period 0<t<4.

2. Relevant equations
integral of p = energy
P=VI

3. The attempt at a solution
Just need the algorithm to solving these kinds of problems, I am kind of thrown off at the instantaneous change.

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2. Sep 13, 2010

### mplayer

One way you could think about this problem is by taking discrete intervals on the current graph and voltage graph and multiplying these values together. This will result in a graph that describes the power dissipation in the device over the given time interval. Then it will just be a matter of finding the area under the curve (integrating the resulting power function).

3. Sep 14, 2010

### Larrytsai

Yeah I thought about that approach but when I look at the voltage it comepletely throws me off. I am able to break the current into 2 seperate intervals with the function y1=25x and 0<t<2, y2=-25x 2<t<4, but for the voltage at t=2 its constant and I cant come up with a function to multply with my current.

4. Sep 14, 2010

### mplayer

For the voltage between t=1 and t=3, the function describing the voltage is just a constant, or y=10.