Download Combo Circuits & EMF

Combo Circuits
& EMF
How much current flows from the
battery in the circuit below?
12V
500
700
400
EMF
Any device (battery) that transforms one type
of energy into electric energy is called a
source of electromotive force (emf)
The potential difference between two
terminals when no current is flowing is called
the emf ()_
When current flows the voltage across the
terminal drops because charge must actually
flow within the source and there is some
internal resistance (r) in the source
The terminal voltage
(Vab) of the source is
thus the emf of the
source minus the
voltage lost to
internal resistance
Vab =  - Ir
This is the voltage
actually delivered by
the source
a
b
Battery
What voltage is actually delivered by a
12V battery (with internal resistance of
.1 ) when a 10 A current flows?
In new batteries the r is usually very
low, but as the battery ages, the
internal resistance increases so it
delivers a lower and lower voltage
For the circuit below with a 9.0V battery (internal
resistance .50) A) How much current is drawn
from the battery? B) What is the terminal
voltage of the battery?
1
5
9V
3
2