Magnetic Effects of Electric Current-Notes

Magnetic field, Field lines, Field due to a current carrying conductor, Field due to current carrying coil or solenoid; Force on current carrying conductor, Fleming’s left hand rule. Electromagnetic induction. Induced potential difference, Induced current, Fleming’s Right Hand Rule, Direct current. Alternating current; frequency of AC. Advantage of AC over DC. Domestic electric circuits.

Magnet has two poles, North pole and South pole. Like poles repel and unlike poles attract.

Magnetic field: The region around a magnet in which the force of attraction or repulsion produced by magnet can be detected.

Magnetic field produced by a conductor at a distance ‘r’ in vacuum is

•  Proportional to current (I).

•  Inversely proportional to the distance ‘r’.

Direction of field is given by Right Hand Thumb Rule

Magnetic lines of force are circular near the wire and become parallel at the middle point ‘M’ of the coil

          •  Proportion al to the current I

          •  Inversely proportional to the radius ‘r’

          •  They do not intersect each other.

          •  The direction of the magnetic field lines is from south to north.

          •  The direction of the magnetic field lines inside the magnet is from North to South.

•  Solenoid: Long coil of many turns of insulated copper wire wrapped in the shape of a cylinder.

•  Magnetic field produced by a solenoid similar to bar magnet.

•  Strength of magnetic field is proportional to number of turns and magnitude of current.

Electromagnets: An electromagnet consists of a long coil of insulated copper wire wound on a soft iron core.

•  A device that converts electrical energy to mechanical energy.

•  Principle: When rectangular coil is placed in magnetic field and current is passed through it coils experience a torque, which rotates it continuously.

•  Phenomenon of inducing an electric current in a coil by changing magi tic field around it.

•  Direction of induced current by Fleming right hand rule (MR):

     Forefinger          - magnetic field

     Centre finger     - induced current

     Thumb                - motion of conductor

•  Converts mechanical energy into electrical energy.

•  AC GENERATOR: Produce current which changes direction after equal interval of time.

•  DC GENERATOR: Produce current which is unidirectional