# Ohm's law

In ohm's law for a receiver or generator I couldn't understood the difference between e/E and U(voltage).
So please can anybody help me in this?

gneill
Mentor
In ohm's law for a receiver or generator I couldn't understood the difference between e/E and U(voltage).
So please can anybody help me in this?

Hi M&I. The use of e, E, V, U, etc., to represent potential difference is a choice made by the author of a diagram or document. Sometimes the choice is personal preference or local convention, or sometimes it's just to avoid duplication if a given variable is already in use for something else.

No matter what variable name is used, all electric potential differences are treated the same way for analysis (Ohm's law, Kirchhoff's law, etc.).

Do you have a particular example where the naming is causing confusion?

In ohm's law for a generator:
U=E-r.I
U voltage
E electro motive force
r resistance
I current

And ohm's law for a receiver
U=e+r.I
e back electro motive force

gneill
Mentor
In ohm's law for a generator:
U=E-r.I
U voltage
E electro motive force
r resistance
I current

And ohm's law for a receiver
U=e+r.I
e back electro motive force

The U,E, and e are representing different potentials in a generator/motor situation. It seems that the author has decided to use U for the "line" potential, e for the back-emf created in the motor's windings (inductance), and E for the potential developed across a generator's windings. The naming convention is designed to help you keep track of what the values represent "in the real world".

The figures in your text might show the inductor potentials as dependent voltage supplies.

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