Download Emf and Terminal Voltage

Emf and Terminal Voltage
V=emf-Ir
ƒ emf is voltage battery 'can deliver' to circuit in principle
ƒ V=emf-Ir is voltage battery 'can deliver' to circuit in
practice. This is called the terminal voltage.
As current flows, the effective voltage, V, is reduced by Ir
emf
I
Battery
V
R
r
(internal resistance of battery)
Application of Ohm's Law indicates
Emf = terminal voltage when I = 0 since Ir = 0
Example
A battery labeled 12.0 V supplies 1.90 A to a 6.00-ohm. What is the
terminal voltage of the battery? What is its internal resistance?
Solution:
emf = 12.0 V
I = 1.90 A
R = 6.00 ohm
V = emf-Ir = IR
ƒ
[like emf = I(r+R)]
V=(1.90 A)(6.00 ohm)=11.4 V
r =
emf − V 12.0 − 11.4
=
= 0.32 ohms
I
1.90