Department of Physics and Astronomy
PHYS 420: Physics Demonstration
THE uncovering of the
theories behind a motor
University of British Columbia
Presenter: Eric Yeh
What are we doing today?
We are going to
learn the basic
functions, principles,
and applications of
an electric motor.
We are also going to
build a very simple
motor today right
here in this
What is a Motor?
A rotating machine that converts electrical
power (either alternating current or direct
current) into mechanical power.
Is this definition very satisfying?
The Types of Motor
DC (Direct Current)
AC (Alternating Current)
Linear Motor
Stepping Motor
Reluctance Motor
The type of motor that
we are going to see
today is a type of DC
Linear Motor
A few countries are
using powerful
electromagnets to
develop high-speed
trains, called maglev
Maglev is short for
magnetic levitation,
which means that
these trains will float
over a guide way
using the basic
principles of magnets.
How Does A Motor Do Work?
There are couple main principles
behind a working DC Motor.
In simple terms, they are:
Ampere’s Law
Right Hand Rule
The Magnetic Field & Force
Torque & Power
How Does A Motor Do Work?
The Electromagnet
Electromagnets are usually in the form of iron
core solenoids.
The iron nails line up with the smaller driving
magnetic field produced by the current in the
This multiplies the magnetic field by factors of
tens to even thousands.
The solenoid field relationship is
k is the relative permeability of the iron, shows
the magnifying effect of the iron core. μ0 is the
permeability of the air.
The Electromagnet
The Electromagnet
The Magnetic Field
The Current
The Current
The Force
Theory Behind a Working Motor
The Torque
Our Demonstration today
The Motor that We are Building
 Materials Required:
One 'D' Cell Alkaline Battery
2 Pieces of Aluminum Tape
Two Large Paper Clips
One Rectangular Ceramic Magnet
Heavy Gauge Magnet Wire (the kind with red
enamel insulation, not plastic coated)
 Fine Sandpaper
 Optional: Glue, Small Block of Wood for Base
The Motor that We are Building
The Motor that We are Building
 Starting about 8 cm
from the end of the wire,
wrap it 7 times around
the battery provided.
 Cut the wire, leaving a
8 cm tail opposite the
original starting point.
 Wrap the two tails
around the coil so that
the coil is held together
and the two tails extend
perpendicular to the coil.
 On one tail, use fine
sandpaper to completely
remove the insulation from
the wire.
 Leave about 0.5 cm of
insulation on the end where
the wire meets to coil. On
the other tail, lay the coil
down flat and lightly sand
off the insulation from the
top half of the wire only.
 Again, leave 0.5 cm of full
insulation on the end and
where the wire meets the
The Motor that We are Building
 Bend the two paper
clips into the following
 Use the aluminum
tape to hold the loop
ends to the terminals
of the "D" Cell battery
 Stick the ceramic
magnet on the side of
the battery as shown:
The Motor that We are Building
 Place the coil in the cradle
formed by the right ends of
the paper clips.
 You may have to give it a
gentle push to get it started,
but it should begin to spin
 If it doesn't spin, check to
make sure that all of the
insulation has been
removed from the wire
The Applications of a Motor
What about a Generator
The current running through coils of
wire would produce magnetic field
that attracts or opposes the existing
permanent magnet, which then
drives the coil of wire to move or
Reversely, coils of wire moves or
rotates in a magnetic field would also
produce a current. This is what a
generate does.
How Does a Generator Work
A Simple Generator Demo
A Simple Generator Demo
A Simple Generator Demo
We are going to try to rotate the
center rod to create current with
the effect of the magnetic field
When we rotate the rod, we will use
a voltmeter to test whether or not
the current is produced.
Also, the positive and negative
current reading depends on the
direction of the spin.
Types of Generator?
Synchronous generators are most
often used for "emergency" or
"standby" power, but in many cases
may be used to provide all of the
power requirements of a facility.
Induction generators are most
often used for "peak shaving"
(providing the power needed for
starting large motors, additional
air conditioning load on hot
days, etc.)
How can Motors and Generators
help us?
With the theory of conservation of energy, we
know that the energy will not disappear. Rather,
energy would change from one form to another.
In our discussion today, we have seen electrical
energy turn into mechanical energy and also from
mechanical to electrical.
Motors would help us to utilize the electrical
energy that we have to do work through the form
of mechanical energy.
Generator does the opposite. It transforms
mechanical energy into electrical energy.
Generator is able to provide us with the source of
electricity when we provide other forms of energy
or materials that could react to release energy.
A Better Definition
• Electric motors involve moving
or rotating coils of wire which
are driven by electric current
producing magnetic force that
opposes the magnetic field.
They transform electrical
energy into mechanical energy.

Here is the PowerPoint slide that I presented to the IB Physics 12 class