Railway Science (Physics-Electric Current and its Effects) (Part-II)

Characteristics of magnetic field lines are: Magnetic lines of force start from the North Pole and end at the South Pole, They are continuous through the body of magnet, Two magnetic lines of force cannot intersect each other. There are magnetic field lines around two bar magnets denoted by A and B. If from A, five lines run from its north pole, then the same number of lines must enter its south pole. In B, ten lines enter its South pole which means ten lines run from its North pole. So, according to the question A's power will be half of B's power.

Magnetic Field is the region around a magnetic material or a moving electric charge within which the force of magnetism acts. Unit - Tesla. Magnetic field lines: used to represent strength magnetic fields. They describe the direction of the magnetic force on a north monopole at any given position. Properties: Magnetic field lines never cross each other, The density of the field lines indicates the strength of the field, Magnetic field lines always make closed loops, Magnetic field lines always emerge or start from the north pole and terminate at the south pole.

Characteristics of the magnetic field produced due to a current-carrying conductor - It encircles the conductor and lies in a plane perpendicular to the conductor, The magnitude of the magnetic field produced is directly proportional to the current passing through the conductor, The magnitude of the magnetic field produced is inversely proportional to the distance from the wire. Direction of magnetic field can be found by Right hand thumb rule - If we hold the current carrying conductor in the right hand in such a way that if the thumb of the right hand represents the direction of the current flow, the rest of the curled fingers determine the direction of the magnetic field around it.

Joule’s law of Heating states that when a current flows in a conductor the amount of heat generated is proportional to resistance (R), time (t) and Square of the current (I). Mathematical expression - H = I²Rt. If resistance and time is constant then ⟹ H ∝ I² . Given I = 3 Then ⟹ H = 3²=9.

Motor converts electrical energy into mechanical energy used as an important component in electric fans, refrigerators, mixers, washing machines. Turbine - converts Hydraulic Energy into Mechanical Energy. Generator - converts mechanical energy into electrical energy.

In Commercial motors Large torque is required to transfer, thus a high strength magnet is required so electromagnets are used. Soft iron is used because it does not retain its magnetism when the current is switched off. The combination of soft iron core and coil is called an armature. It enhances the power of the motor.

Brushes in electric motors - used to transfer power between the rotating armature coils and stationary wires to the rotor. Armature - a device through which electric current is passed for generating torque. Electric motor - Invented by Michael Faraday in 1821. Electric generator - follows Fleming Right hand rule.

An electromagnet is made by winding an insulated copper wire around a soft iron core either in the shape of a solenoid or U-shape and passing current through it. Uses - Amplifiers, MRI (Magnetic resonance imaging) machines, Transportation, Spacecraft Propulsion Systems.

An object which is capable of producing magnetic fields and attracting unlike poles and repelling like poles. Properties of Magnet - Magnetic poles always exist in pairs. Like poles repel while unlike poles attract. The magnetic force between the two magnets is greater when the distance between the magnet is lesser. Types of Magnets - Permanent magnet, Temporary magnet, Electromagnets.

The strength of the magnetic field produced by the solenoid can be increased : By placing soft iron inside the solenoid, By increasing the number of turns of the coil and By increasing the current flowing through the solenoid. The combination of the solenoid and the soft iron core is called an electromagnet. Electromagnet is formed when current is passed through a coil wound around a soft iron core.