Fleming's left-hand rule:
According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.
Devices that use current-carrying conductors and magnetic fields:
Electric motor, electric generator, loudspeakers, microphones and measuring instruments etc.
Magnetism in medicine:
MRI: The magnetic field inside the body forms the basis of obtaining the images of different body parts. This is done using a technique called Magnetic Resonance Imaging (MRI).
Propertie of magnetic field inside the body:
- Magnetic field is produced in our body which travels along the nerve cells.
- This nerve impulse produces a temporary magnetic field.
- These fields are very weak and are about one-billionth of the earth’s magnetic field.
- Human heart and brain are two organs which produce magnetic field.
An electric motor is a device which converts electric energy into mechanical energy.
Uses of Electric Motor: Electric fans, mixers, grinders, blenders, cutters, DVD players, computers, washing machines etc.
Principle of Electric Motor: An electric Motor works on the principle that a current carrying conductor experiences a force when placed in a magnetic field. If the direction of the magnetic field and that of the direction of current which pass through the magnetic field are mutually perpendicular then the direction of the force is given by Fleming’s left-hand rule.
(A) Split rings: These are cylindrical shape metalic rings which are divided into two halves. The inner sides of these halves are insulated and attached to an axle.
Role of split rings in Electric Motor:
It works as commutator in electric motor that reverses the direction of the flowing of electric current.
Commutator: Commutator is a device which is used to reverse the direction of the flowing of electric current.
(B) Armatures: It is a rectangular coil which has a large number of turns of thin insulated copper wire turned over a soft iron core. The armature is placed between the two poles of the field magnet such that the arm AB and CD are perpendicular to the direction of the magnetic field.
Role of armature in Electric Motor:
(i) The armature operates by rotating along with a magnetic field.
(ii) The armature will rest when the resultant field is aligned with the stator (or static) field.
(C) Axle: Axle is a rotating rod like structure which is situated in the centre of armature and split rings are fitted on it.
The properties of commercial motors: Commercial motors are powerful motors. Due to following properties these are powerfull.
(i) Electric magnet is used in commercial motor inspite of parmanent magnet.
(ii) No of turns of insulated copper wire is more in current carrying coil.
(iii) Soft iron crode is used to wrap the coil, by which power is incresed.