# Voltage vs. Time Graph

1. Oct 20, 2009

### megr_ftw

What are you able to derive or integrate from a voltage vs. time graph? Like if I have a battery and a resistor and want to know the charge after so many hours or seconds.
We went over this in class but could someone elaborate the relationship?

2. Oct 20, 2009

### mikelepore

A battery across a resistor, voltage is constant, graph of voltage versus time is a horizontal straight line. Are you sure that your real question isn't about a capacitor?

3. Oct 20, 2009

### megr_ftw

I had a problem the teacher gave us and it was a graph of time(x-axis) vs. voltage(y-axis) and it had the line as a negative slope where the voltage of the battery was 1.5V and it crossed the y-axis at 3 hours. they gave us a resistor of x ohms.
So there is no capacitor in the problem and how should I treat it?

*note this is not a homework question, just a general one

4. Oct 21, 2009

### elliotr

You're question is a bit confusing... I'll try to help...
I'll assume:
-You're saying the battery's voltage is reducing linearly from 1.5V to 0V over a three hour duration.
-You're circuit is a battery with a resistor across it.
-You said something about charge, so I'll assume current.

Current, I=V/R

If you integrate that function, you get 0.5*(1.5V)/R*time. For example, let's assume that R=10 Ohms:
Then you could calculate: 0.5*1.5/10*3hr = 225mAh (milli amp hours).

But this is actually a useless calculation. Can you elaborate on your question?

5. Oct 21, 2009

### mikelepore

I think the person needs:
decreasing 1.5 volts in 10800 seconds, for a slope of -0.0001389 volts per second
V = (-0.0001389 V/s) t + 1.5 V