# Differences between two Voltage formulas

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1. Mar 6, 2015

### sawer

What is the differences between these two voltage formulas.
1. for a point charge: $$V = k\frac{q}{r}$$
2. for an inductor: $$V(t)= L\frac{di}{dt}$$

Why are there different voltage formulas? Can second one be derived from the first one?
Or do they completely represent different concepts?

2. Mar 6, 2015

### sophiecentaur

The two expressions refer to different circumstances; sub-sets of the general case. If you look at Maxwell's equations then you will see how it all ties together.
It is common for equations describing phenomena to share a variable.

3. Mar 6, 2015

### sawer

Can you please give some hints

4. Mar 6, 2015

### sophiecentaur

Just think of the suvat set of equations used for calculations in dynamics. There is always a choice of how to express things in terms of different variables. Are you looking for some extra significance in this?

5. Mar 6, 2015

### Staff: Mentor

Well, what is generating the voltage in each case?