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Take Home Lab #2
simple motor
Objective
To investigate the electromagnetic principles behind the operation of a simple D.C. motor.
Introduction and Theory
In this lab you will construct a very simple D.C. motor and answer some questions about
how it works.
An electric motor is a device for converting electrical potential energy into rotational kinetic
energy. The electrical energy which powers the motor you will be making in this lab comes
from an alkaline battery. The battery provides an electric potential, which causes a current
to flow through a coil of wire. If the coil is placed in a magnetic field while there is current
running through it, the magnetic field will exert a force on the coil, causing it to turn.
For more on D.C. motors see Giancoli 27.5 or the Interactive Notes on Magnetism.
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Apparatus
• 1 ‘D’ cell alkaline battery
• 1 battery holder with attached paper clips
• 1 rare-earth magnet (silver)
• 1 ceramic magnet (black)
• 1 wooden block
• enameled wire
• fine sandpaper
Procedure
Winding The Coil
1. Starting about 4 cm from the end of the wire, wrap it 7 times around the wooden
block. Remove the block (you don’t need it any more). Cut the wire, leaving a 4 cm
tail of wire 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. See
illustration below:
Seven loops
Tail (4cm)
Tail is wrapped
around the coil
to hold the coil
together and to
hold the tail in
position.
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Note: Be sure to center the two tails on either side of the coil. Balance is important.
2. On one tail, use fine sandpaper to completely remove the insulation from the wire.
Leave about 0.5 cm of insulation on the end and 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 coil.
Cross-section
of wire
Insulation
Left Tail
Right Tail
Constructing The Motor
1. Place the coil in the cradle formed by the bent paper clips.
If the coil is properly balanced, it should be horizontal when it comes to rest (i.e. its
surface vector should be vertical). If it does not, adjust the tails until it does.
2. Stick the rare-earth magnet on the side of the battery holder, as shown below:
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Magnet
Give the coil a gentle push to get it started; it should begin to spin rapidly. If it
doesn’t spin, check to make sure that all of the insulation has been removed from the
wire ends. If it spins erratically, make sure that the tails on the coil are centered on
the sides of the coil.
instructions inspired by home.hiwaay.net/∼palmer/motor.html