Internal Resistance

Question 1

What is the equation for electromotive force

Answer 1

Emf = I(R+r)

Question 2

How do you rearrange it to find internal resistance?

Answer 2

If Emf = I(R+r), then it equals V+Ir

Simply do:
E = I(R+r)

Next:
E = V+Ir

Then:
E-V = Ir
Then: (E-V)/I = r