#### Transcript A circuit must contain a source of potential difference, and a path for

```Unfortunate
book
names:
A circuit must contain
a source of potential
difference, and a path for
the flow of charge. It will
probably also contain a
(a user of energy).
Charges moving through a cell
experience a voltage rise equal
to the potential difference
between the terminals. As the
charge moves through the
external circuit it experiences a
voltage drop equal in magnitude
to the initial voltage rise.
In any circuit, the total
of all voltage rises is
equal to the total of all
voltage drops. This is
one of Kirchoff’s laws
for electric circuits.
The emf of the circuit is the
drop in potential across the
total circuit, but Ohm’s law
(V = IR) applies equally
well to any part of circuit
that does not include a
source of emf.
If a circuit contains a
R, and a source with an
emf , the current in the
entire circuit is
I = /R.
A battery has an emf of
has a resistance of 6
ohms. What are the
total resistance and
current of the circuit?
For a part of the circuit
Ohm’s law is: V = IR.
What is the drop in
potential across the
external circuit in the
previous example?
Notice that the
drop in potential
total emf of the
battery.
A good voltmeter has a high
resistance. If it is connected
across the terminals of a
source of emf, negligible
current is drawn from the
source and the voltmeter
registers the emf of the
source.
A dry cell gives an opencircuit voltmeter reading of
1.5 V. The voltmeter is then
removed from the circuit