Download Electric Potential Energy and Voltage

8.1 - Electric Potential Energy and Voltage :
(page 250)
We store electrical charges inside
“electrochemical cells”.(what a consumer would call
a battery) They change chemical energy into
electrical energy.
How ?
They keep oppositely charged substances
separated inside them, creating a difference in
energy between two places ( terminals ).
(stretched spring or
climbing stairs analogy)
Why ?
These cells are energy sources. Energy is the
ability to do work. Potential energy is the energy
stored inside an object. Electric potential energy is
the energy stored inside these things because of
separated charges, and they have the ability to do
work when hooked up to a path (“circuit”) and
electrons can flow around this path. (electrical
kinetic energy)http://www.explainthatstuff.com/how-lithium-ion-batteries-work.html
How Stored Energy is Measured :
The amount of energy it takes to make one
coulomb of stored charge is called the “potential
difference” or “voltage” ( after the Italian physicist Alessandro Volta). It
is a measure of how much energy the cell can put
out.
A battery’s potential energy depends on 2
things....
how much voltage the battery has ( the
difference in potential energy between 2
parts....how different they are in terms of
giving up electrons
the amount of separated charge ( how many
electrons we have separated)
Voltage of a cell is measured using a
“voltmeter”.
or
Different cells might be marked as having the
same voltage...but the one that has the largest
separated charges and more coulombs of force has
more potential energy in it.
Types of Cells and How They Work : (253)
http://michaelbluejay.com/batteries/
C - Zn :
Lithium : http://electronics.howstuffworks.com/lithium-ion-battery1.htm
Batteries.....
Each has two “terminals” or “electrodes” made of 2
different metals ( sometimes a metal and
carbon/graphite )...A negative (anode) terminal
(where electrons are concentrated) and a positive
(cathode) terminal (where there are fewer electrons).
There will also be an “electrolyte”, or substance that
conducts electricity between the two electrodes.
This is a paste or gel on a “dry cell”, and it is a
liquid in a “wet cell”.
One electrode reacts with the electrolyte to give up
atoms, leaving some E behind (-), the other
electrode gives up electrons ( +) and a difference
(voltage) is created.
Modern Battery Chemistry
Modern batteries use a variety of chemicals to power their reactions. Typical battery chemistries
include:
Zinc-carbon battery - Also known as a standard carbon battery, zinc-carbon chemistry is used
in all inexpensive AA, C and D dry-cell batteries. The electrodes are zinc and carbon, with
an acidic paste between them that serves as the electrolyte.
Alkaline battery - Alkaline chemistry is used in common Duracell and Energizer batteries, the
electrodes are zinc and manganese-oxide, with an alkaline electrolyte.
Lithium-iodide battery - Lithium-iodide chemistry is used in pacemakers and hearing aides
because of their long life.
Lead-acid battery - Lead-acid chemistry is used in automobiles, the electrodes are made of lead
and lead-oxide with a strong acidic electrolyte (rechargeable).
Nickel-cadmium battery - The electrodes are nickel-hydroxide and cadmium, with potassiumhydroxide as the electrolyte (rechargeable).
Nickel-metal hydride battery - This battery is rapidly replacing nickel-cadmium because it
does not suffer from the memory effect that nickel-cadmiums do (rechargeable).
Lithium-ion battery - With a very good power-to-weight ratio, this is often found in high-end
laptop computers and cell phones (rechargeable).
Zinc-air battery - This battery is lightweight and rechargeable.
Zinc-mercury oxide battery - This is often used in hearing-aids.
Silver-zinc battery - This is used in aeronautical applications because the power-to-weight ratio
is good.
Reading Check Questions 1-9, page 255
“Many Sources of Electrical Energy”, page 254
Electric eel and electrogenic cells , page 258
Science uses the term “battery” to refer to a
number of these cells connected together.
The voltage ( electric potential) of a “battery” is
the total of all individual cells added together.
Ex.
Combining six 1.5 volt “cells”
together makes a 9 volt “battery”
8.2 - Electric Current :
(page 260)
“Current electricity” is the flow of charged particles
around a path ( “circuit”). Current is measured in
“amperes” (A). One amp = 1 coulomb of electrons
passing a point on the path per second. Aperes can
be measured using an “ammeter”.
Or
Circuits :
When the two terminals are connected by one
shared conductor, electrons can flow through a
completed “closed” or unbroken path to make
something work or move (the “electrical load”).
Loads could be sound devices, light, motors, or heat
generating devices. They cause a drop in voltage
returning to the cell, since some of the potential
energy is transformed into heat, light, sound or
movement.
All circuits include...
An energy source A conducting path A control switch -
An electric load -
Water slide analogy - page 261
(Cells, batteries, or
devices from page 254)
( wire )
(opens or closes the
path to control electron
movement)
(Devices converting
current electricity into
light, sound, heat, or
some other form)
Simple circuits can be sketched using a standard set
of symbols ( page 262 ) and rules. These “circuit
diagrams” are square or rectangular drawings that
show what all parts of a circuit are, and how they
are connected.
Reading check questions - page 262
Drawing circuits, page 263