Transcript the motor principle

THE MOTOR PRINCIPLE
THE ELECTRIC MOTOR

many devices depend on the electric motor
including:
 fans
 computers
 elevators
 car
windows
 amusement park
rides
MOVING CONDUCTORS WITH ELECTRICITY
Michael Faraday (1821) wanted to see if a
magnet could move a conductor just like a
conductor could move a compass needle
 his experiment was successful and he created
the first electric motor
 the motor worked because the magnetic field in
the copper wire interacted with the
magnetic field of the permanent bar
magnet

INTERACTION OF MAGNETIC FIELDS
one magnetic field is from a current-carrying
conductor, the other is from the external
magnets
 when the two interacting magnetic field lines
are pointed in the same direction there is a
repulsion force
 when the interacting field lines are pointed in
opposite directions, there is an attraction force
 the final result is the conductor being forced
downward

INTERACTION OF MAGNETIC FIELDS
THE MOTOR PRINCIPLE
describes movement of a current-carrying
conductor in an external magnetic field
 “a current-carrying conductor that cuts across
external magnetic field lines experiences a
force perpendicular to both the magnetic field
and the direction of the electric current”
 magnitude of the force depends on the
magnitude of the external field and magnitude
of the current

RIGHT HAND RULE

hold your hand flat with your thumb at a rightangle to your fingers

if the fingers point in the direction of the
external magnetic field and your thumb points
in the direction of the conventional current,
then your palm faces the direction of the force
on the conductor
RIGHT HAND RULE FOR MOTOR PRINCIPLE

note: if you follow electron flow instead of
conventional current, then use the left-hand
rule
ANALOG METERS

one of the first practical uses of the motor
principle was the development of meters
measuring electrical quantities
AMMETER AND VOLTMETERS
are both made from a galvanometer and a
resistor that protects the sensitive coils of the
looped wire
 both ammeter and voltmeters actually measure
current, but the voltmeters scale is determined
by the Ohm’s law relationship, yielding voltage

SUMMARY
an external magnetic field can cause a currentcarrying conductor to move
 the motor principle states that the currentcarrying conductor experiences a force
perpendicular to both the magnetic field and
the direction of the electric current
 the magnitude of the force on a currentcarrying conductor depends on both the
magnitude of the external magnetic field and
the magnitude of the current

SUMMARY
the right-hand rule for motor principle states
that if the fingers point in the direction of the
magnetic field lines and your thumb points in
the direction of the conventional current, then
your palm faces the direction of the force on
the conductor
 analog meters operate according to the motor
principle

PRACTICE