# Thread: Numerical Differntiation with impressed voltage equation

1. ## Numerical Differntiation with impressed voltage equation

Problem statement:

In a circuit with impressed voltage E(t) and inductance L, Kirchhoff's first law gives the relationship:
$\displaystyle E(t) = L * \frac{di}{dt} + Ri$
where R is the resistance in the circuit and i is the current. Suppose we measure the current for several values of t and obtain:
t | i
1.00 | 3.10
1.01 | 3.12
1.02 | 3.14
1.03 | 3.18
1.04 | 3.24

where t is measured in seconds, i is in amperes, the inductance L is a constant 0.98 henries, and the resistance is 0.142 ohms. Approximate the voltage E(t) when t = 1.00, 1.01, 1.02, 1.03, and 1.04.

Question:

I have been looking at this problem for a couple of days. I am unsure of where to begin with this. Can anyone give me a hint or advice to get this problem started?

2. $\displaystyle \displaystyle \left\phantom{|}\frac{di}{dt}\right |_{t = 1} \approx \frac{i_{1.1} - i_1}{t_{1.1} - t_1}$.

Follow a similar method to approximate $\displaystyle \displaystyle \frac{di}{dt}$ at the other times.

3. Thanks for the help. Sometimes the simplest solutions are the hardest to figure out.