Q. 214.2( 22 Votes )

# (a) State Fleming

Fleming’s left-hand rule is a method to determine the direction of force acting on the conductor that is kept in a uniform magnetic field. It is not a process to determine the magnitude of the force but the direction of any of the three parameters; current, magnetic field and the force when the direction of two of the three parameters are known.

It states “Hold your thumb, the forefinger and the second finger at a right angle to each other. If the forefinger represents the direction of the field and the second finger represents that of the current then thumb gives the direction of the force”

Fig – Fleming’s Right-Hand Rule

(b) A motor is a device that converts electrical energy into mechanical energy.

The principal of Electric Motor: When a current carrying coil is placed in a magnetic field and current is passed through it, the coil experiences a force.

The direction of force is determined using Fleming’s left-hand rule.

The coil ABCD is placed in between two magnetic poles in such way that the arms of the coil AB and CD are perpendicular to the direction of the magnetic field. As the coil draws current from the battery source, it experiences a force, determined using Fleming’s left-hand rule. The forces cause the coil to rotate continuously generating useful mechanical energy.

(c) (i)Armature: Armature is a mechanical component of an electric motor. The armature is supplied with the current and it experiences a force.

The function of the armature can mainly be described in the following ways:

(a)The armature is responsible for carrying the current across the magnetic field.

(b)The armature is the element in the electric motor that induces and sustains the rotary motion in the electric motor.

(ii)Brushes: Brushes, sometimes known as motor brush, are a small component of an electric motor that enables the delivery of current from the stationary wire to the rotating wire in an electric motor. They are usually made up of carbon material. In the electric motor, the brushes are mounted on the stationary wire circuit of the motor as shown in the figure, X and Y. They operate together with the slip rings to accomplish the commutation of current in the electric motor.

(iii)Slip rings: Slip rings are a device that reverses the direction of flow of current in an electric motor through a circuit is known as a commutator. P and Q are the split rings as shown in the figure. The reversal of current also, in turn, reverses the direction of force acting on the armature. Earlier the upward force acting on the coil segment AB is now pushed down, similarly, the downward force acting on the coil segment CD is reversed to upward force.

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