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ARMATURE (Rotor): The armature is made up of one or more electric windings around armature arms. BRUSHES: As the motor turns the brushes slide over the commutator segments hence creating the variable magnetic field in different arms through the commutator segments attached to the windings.
The brushed DC motor has a mechanical sliding contact between the brushes and the commutator collar. After studying this section, you will (a) understand what is meant by the "motor effect", (b) know the basic principle which underlies the operation of galvanometers, and (c) understand the basic priciple of the operation of simple direct-current motors. This is demonstrated by the following experiment: if a conductor is placed between the poles of two bar magnets that are aligned as shown in the diagram on the right, and a current allowed to flow as shown, the conductor will suddenly jump to the right. The magnitude of the force on the conductor depends on the magnitude of the current which it carries.
The greater the length of the conductor perpendicular to the magnetic field, the greater the force on it.The direction of the force is defined by the diagram on the left, where the axes are at right angles to each other. If you point your left forefinger in the direction of the magnetic field, and your second finger in the direction of the current flow, then your thumb will point naturally in the direction of the resulting force!
The tesla is the density of a magnetic field such that a conductor carrying a current of 1 ampere at right angles to that field has a force of 1 newton acting upon it. The force that is exerted on a current-carrying conductor in a constant magnetic field is dependent on the strength of the current - the greater the current, the greater the force on the conductor. A wire carrying the current to be measured is wound as shown on the right around a soft iron core.
The principle that a current flowing through a conductor which is placed in a magnetic field results in a mechanical effect, that is the conductor experiences a force, is exploited in ELECTRIC MOTORS, essential components of our day-to-day life.
In its most basic form, an electric motor consists of a rectangular coil of insulated wire, which makes up the armature, or moving part of the motor.
The brushes serve to make contact between the battery and the rotating commutator, which is mounted on an insulated shaft, not shown in the picture. When the current is switched on, it flows in opposite directions along the two segments of the coil, generating equal but opposite thrusts, which form a couple tending to rotate the coil.


If the direction of the current, or if the poles of the magnet, are reversed, rotation will proceed in the opposite direction. Magnetism is an invisible force or field caused by the unique properties of certain materials. Turn one magnet around, and the North (N) and the South (S) poles are attracted to each other. Only a few materials have the right type of structures to allow the electrons to line up just right to create a magnet. This site is a product of TSI (Technological Solutions, Inc.), Copyright 2016, All Rights Reserved. The stator generates a stationary magnetic field around the rotor which occupies the central part of the motor.
Hence a dynamic magnetic field is generated in the motor when a voltage is applied across the brushes.
If either the current flow or the polarities of the magnets are reversed, the conductor will move in the opposite direction. Note that heat is also produced, so there is never a 100% conversion of electrical energy into mechanical energy. By wrapping a wire around an iron bar and running current through the wire, very strong magnets can be created.
There is a stator (a larger stationary part) and a rotor (a smaller part spinning on an axis within the stator). The magnetic poles thus generated by this rotor field are attracted to the opposite poles generated by the stator field and repelled by the similar poles, which causes the armature to rotate.
The current flow causes a force which tends to twist the wire, and this is seen as a needle deflection.
The outer portion of the core is liquid iron that spins and makes the earth into a giant magnet.
There are magnets on the stator and a coil on the rotor which is magnetically charged by supplying current to it.
The internal circuits built into these instruments will determine whether they will be used to measure current, in which case they are called AMMETERS, or whether they will be used to measure potential difference, in which case, they are called VOLTMETERS.
The deflection is measured on a scale (not shown) which is calibrated in units of current or potential difference.


Brushes are responsible for transferring current from the stationary DC voltage source to the spinning rotor.
The brushes deliver current from a DC voltage source which supplies a magnetic field to that end of the rotor.
In magnets the molecules are uniquely arranged so that their electrons spin in the same direction.
Depending on the position of the rotor its magnetic charge will change and produce motion in the motor.
This arrangement of atoms creates two poles in a magnet, a North-seeking pole and a South-seeking pole.
This is very useful to us here on Earth as it lets us use magnets in compasses to find our way and make sure we are heading in the right direction. As the rotor turns the brushes make contact with one side of the DC source, then briefly do not make contact with anything, then continue making contact with the other side of the DC source effectively changing the polarity of the rotor. It's also useful to animals such as birds and whales who use the Earth's magnetic field to find the right direction when migrating.
The timing of this change is determined by the geometrical setup of the brushes and leads to the DC source. Perhaps the most important feature of the Earth's magnetic field is that it protects us from the Sun's solar wind and radiation. To control speed an in-line variable resistance can be utilized to change the amount of current reaching the coils.
The animation helps to illustrate how at the moment of maximum attraction the current will change direction and thus change the polarity of the rotor. At this moment the maximum attraction suddenly shifts to maximum repulsion which puts a torque on the rotor's shaft and causes the motor to spin.



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