Physics help?Terminal voltage question?

Question

where does the equation (E-Ir=IR) comes from where E=EMF ,I=current, R=external resistor and r= internal ressistance.

Answer 1

http://farside.ph.utexas.edu/teaching/302l/lectures/node43.html

Answer 2

The voltage source equivalent model (Thevenin Equivalent) of a battery consists of a perfect voltage source E in series with a resistor r (called the Thevenin equivalent source resistance). When current is flowing from the - to + node, there is a voltage drop across the internal resistance which is Ir so that the effective terminal voltage becomes E - Ir. This is the terminal voltage and the rest is simply Ohms Law.

Doug

Answer 3

You have not mentioned the terminal voltage in your question.

Actually E- Ir = V, the terminal voltage

It comes from Ohm's law, which we take on faith.

r is the internal resistance, which accounts for the voltage drop Ir when a current I is supplied.

So the actual voltage from the battery we get is V= E- Ir the terminal voltage, which decreases as the I decreases.