PSAA Curriculum
Unit
Physical Science Systems
Problem Area
Energy and Power Systems
Generating an
Electromotive Force
Lesson
What is needed to produce
energy?
Can electricity be produced with two nails
and a piece of fruit?
Multimeter
What electrical
measurements can
be taken with this
meter?
What are some
practical uses for
these
measurements?
Learning Objectives
Generate an electromotive force by means
of chemicals, magnetism, heat, and solar
radiation.
Construct a primary cell and understand
its function.
Learning Objectives
Explain the function of a voltmeter and
construct a voltmeter circuit, which is the
same type as used in commercial
voltmeters.
Properly connect a voltmeter to a circuit
and measure voltage in a circuit.
Terms
Ammeters
Cell
Conductor
D’Arsonval meter
movement
Electricity
Electromotive force
Electrons
Linear scale
Magnetic field
Multimeters
Nonlinear scale
Solar Cell
Square-law scale
Voltmeter
What different methods can be
used to generate an electromotive
force?
Electricity is a form of energy present when
electrons move through a complete path.
Electrons are negatively charged atomic particles
that normally revolve around the nucleus of an
atom.
The force that causes the electrons to move
through the path is voltage or electromotive force.
The path the electrons follow through easily is a
conductor.
What different methods can be
used to generate an electromotive
force?
The most popular commercial method of
generating an electromotive force is by means of
magnetism.
A coil of wire has a moving magnetic field
passed through it and thus produces an
electromotive force.
This type of generation occurs in an alternator in
an automobile or in the large generators used to
produce electricity for the home.
Magnetism
In 1820, Danish physicist, Hans
Oersted discovered that a compass
needle could be deflected by an
electric current.
Until that time, it was generally
thought electricity and magnetism
were completely different.
Magnetism (cont.)
In order for there to be a reading on a
voltmeter, for example, a force must act
upon the charges that are moving along
the magnetic field lines.
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
If the charge is not moving or is moving in the
same direction as the magnetic fields, then
there is no force.
But, if the charge is moving across the field
lines, then the charge has force acting upon it
and an electrical current can be measured.
Magnetism (cont.)
Hans Oersted showed that electricity can
have an effect on magnetic fields, but it
wasn’t until 1832 that Michael Faraday
showed that magnetic fields could have an
effect on electrical currents.
This is called the complementary effect
and is demonstrated in this experiment.
What different methods can be
used to generate an electromotive
force?
Emf (electromotive force) by chemical
reaction was discovered by Anastasio
Volta who invented the first battery by
discovering that certain combinations of
metals produced an electromotive force.
Electromotive Force (Emf)
Emf by heat is demonstrated by the use of
a thermocouple, a device that consists of
the junction of two dissimilar metallic
conductors, such as, copper and iron.
An emf is induced when the conductors
are maintained at different temperatures.
Electromotive Force (Emf)
Emf by solar radiation is demonstrated by
the photovoltaic cell.
This solar cell has the capacity to convert
light directly into electricity without having
a heat engine (defined as any device that
changes thermal energy into mechanical
work) involved.
Emf by magnetism was discussed earlier
in this lesson.
Solar Cell
What is a primary cell? How does a
cell generate electromotive force?
Chemical reaction is one of the six basic
forms of energy (Others include friction,
magnetism, pressure, heat, and light).
Chemical energy is converted into
electrical energy by a device known as a
cell.
Two or more cells connected form a
battery.
Primary Cells
Primary cells can be recharged using only
new materials while secondary cells are
rechargeable without replacing materials
used to make the cell.
The lead-acid storage battery is a type of
secondary cell.
How does a cell generate
electromotive force?
Each cell in the battery has two groups of
coated lead plates known as electrodes.
The positive plate is made of lead
peroxide and the negative plate is made of
lead.
The electrodes are separated from each
other and immersed in a liquid solution
called an electrolyte.
How does a voltmeter function and
how can we construct a voltmeter
circuit?
A voltmeter circuit contains a d’Arsonval
meter (similar to a galvanometer) and an
extremely high ohm resistor in series with
the meter.
How does a voltmeter function?
A linear scale on the meter has readings
divided into equal portions.
A nonlinear scale on the meter is marked
off by uneven spaces.
Voltmeters indicate the amount of voltage
present in the circuit, ammeters measure
current flow through the conductor, and
ohmmeters indicate electrical resistance.
How does a voltmeter function and
how can we construct a voltmeter
circuit?
Multimeters are capable of measuring
more than one characteristic of a circuit,
i.e. voltage, amperage, and resistance.
Multimeters usually show both linear and
nonlinear scales.
A square-law scale is a type of nonlinear
scale which increases by squares.
Each larger scale marking indicates that
the measured value is multiplied by itself.
How does a voltmeter function and
how can we construct a voltmeter
circuit?
d’Arsonval meter movement is the portion of the
meter consisting of a fixed permanent magnet and a
moving electromagnetic coil.
The voltmeter is calibrated to show the amount of
voltage which would cause an amount of current to
flow through the carefully selected resistance of the
voltmeter.
The voltmeter is current sensitive.
The extent of the movement of the meter pointer is
directly proportional to the amount of current flowing
through the meter.
How is a voltmeter used to properly
measure voltage in a circuit?
A voltmeter is always connected in parallel
in a circuit.
It is put across a resistor or voltage
source.
The multiplier resistor allows for varying
degrees of accuracy when using a
multimeter for ampere, ohms, and volt
readings.
Connecting a Voltmeter in
parallel to a test circuit.
What is a voltage drop?
Voltage drops occur in power lines running
from the transformer to the circuit box and
in the wiring inside a building.
A small amount of power is always lost as
electricity flows through the wires.
The energy loss is measured as voltage
drop.
The voltage drop is calculated by
multiplying the current times the
resistance.
Review/Summary
What different methods can be used to
generate an electromotive force?
What is a primary cell?
How does a cell generate electromotive
force?
Review/Summary
How does a voltmeter function and how
can we construct a voltmeter circuit?
How is a voltmeter used to properly
measure voltage in a circuit?
What is a voltage drop?