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Potential Difference
LESSON 7
N O V E M B E R 1 5 TH, 2 0 1 0
Potential Difference
Each electron has electric potential energy.
 Potential energy is the energy stored in an
object.
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Example: An apple hanging from a low. The apple has potential
energy because of its position above the ground. If the apple falls
down, it will convert its stored energy, or potential energy, into
motion. An apple at a higher branch. It would have even more
potential energy to convert.
Potential Difference
A battery has chemical potential energy in the
electrolyte in its electrochemical cells.
 The chemicals in the electrolyte react with
the electrodes.
 This causes a difference in the amount of electrons
between the two terminals.
Potential Difference
One terminal in a battery has mainly negative charges
(electrons).
 The other terminal has mainly positive charges.
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 The negative charges are electrons, which can move
are attracted to the positive charges at the positive
terminal.
Potential Difference
 If a conductor, such as a copper wire, is connected to
both terminals, then the electrons flow from the
negative terminal to the positive terminal.
 The difference in electric potential energy
between two points in a circuit is called the
potential difference or voltage (V).
Potential Difference
 This difference causes current to flow in a closed
circuit. The higher the potential difference in a
circuit, the greater the potential energy of each
electron.
Measuring Potential Difference
 The potential difference between two locations in a
circuit is measured with a voltmeter.
Measuring Potential Difference
 Example: Connecting wires from a negative terminal
on a battery across a voltmeter and then back to the
positive terminal. The voltmeter would then display
the potential difference of the battery.
 The SI unit for measuring potential difference is the
volt (V).
Electrochemical Cells – Batteries
 A battery is a combination of electrochemical cells.
Each electrochemical cell is a package of chemicals
that converts chemical energy into electrical energy
that is stored in charged particles.
 A simple electrochemical cell includes an electrolyte
and two electrodes.
Electrochemical Cells – Batteries
 An electrolyte is a liquid or paste that
conducts electricity because it contains
chemicals that form ions.

An ion is an atom or a group of atoms that has become
electrically charged by losing or gaining electrons.
Sulphuric acid is an example of an electrolyte.
Electrochemical Cells – Batteries
 Electrodes are metal strips that react with the
electrolyte. Two different electrodes, such as zinc and
copper, are used in a battery.
 The electrodes and electrolyte react causing
one electrode to collect and the other to lose
electrons.
Wet Cells and Dry Cells
An electrochemical cell that has a liquid
electrolyte is called a wet cell.
 Wet cells are often used as an energy source for cars
and other motorized vehicles.
 An electrochemical cell that uses a paste instead of a
liquid electrolyte is called a dry cell.
Wet Cells and Dry Cells
 An electrochemical cell that
uses a paste instead of a liquid
electrolyte is called a dry cell.
 Dry cells are used in flashlights,
hand-held video game devices,
cameras, and watches. Each electrode
in a dry cell or battery can also be
called a terminal. Terminals are the
end points in a cell or battery where
we make a connection
Recycling and Recharging Dry Cells
 Eventually, the chemicals in a dry cell are used up
and can no longer separate charges. Dry cells should
be recycle rather than discarded.
 Dry cells can contain toxic materials, such as
the heavy metals nickel, cadmium, and lead.
 Household dry cells and batteries are responsible for
over 50 percent of all the heavy metals found in
landfills.
Recycling and Recharging Dry Cells
 Some dry cells are rechargeable cells. Chemical
reactions in a rechargeable cell can be reversed by
using an external energy source to run electricity
back through the cell.
 The reversed flow of electrons restores the reactants
that are used up when the cell produces electricity
Recycling and Recharging Dry Cells
 Since rechargeable dry cells can be reused many
times, they have less impact on the environment
than non-rechargeable dry cells.
Fuel Cells
 A fuel cell is an electrochemical cell that generates
electricity directly from a chemical reaction with a
fuel, such as hydrogen.
 The cell is not used up like an ordinary cell
would be because as the electricity is
produced, more fuel is added.
Fuel Cells
 Much of the energy produced by fuel cells is wasted
as heat, but their design continues to be refined. Fuel
cells are used in electric vehicles and may one day be
used in smaller devices such as laptop computers.
Fuel Cells
Questions
 1. How is current electricity different from static
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electricity? I (1)
2. What is the difference between an electrolyte and
an electrode? I (1)
3. Why should dry cells be recycled rather than
thrown in the trash?K (1
4. What is another name for stored energy? K (1)
5. What does potential difference measure? K (1)