Railway Science (Physics-Electric Current and its Effects)

Factors affecting the force experienced by a straight conductor placed in a magnetic field - Depends on current, magnetic field and length of the conductor. Magnetic field due to a straight current-carrying conductor - When current is passed through it, a magnetic field is produced around it. Magnetic field due to current through a circular loop - Every point on the wire carrying current gives rise to a magnetic field that appears as straight lines at the center.

The magnitude of the magnetic field (B) is directly proportional to the magnitude of current (I) through the loop, inversely proportional to the radius (r) of the circular loop, and depends upon the number of turns (n) in the current-carrying loop, that is B ∝ nI/r . The larger the number of turns, the higher the magnitude of the magnetic field.

According to Ohm's Law, i.e. V = IR ⇒ I = V / R So, we can see that resistance and current are reciprocal to each other. If the resistance increases, the current decreases. So if the resistance is increased 4 times, then the current decreases to one fourth of the previous value.

Ohm’s law V-I graph characteristics - This graph will be of a linear equation that will pass through the origin. The V-I graph will be a straight line. As the value of voltage increases in the circuit, the value of the current will also increase provided the resistance of the circuit does not change. The ratio of voltage and current will remain constant in all phases.

An electric generator is a device that changes kinetic energy to electrical energy through electromagnetic induction. Electromagnetic induction is the process of generating electric current with a magnetic field. It occurs when a magnetic field and an electric conductor, such as a coil of wire, move relative to one another.

The coil which is connected to the battery will act as an electromagnet i.e. coil A. So whenever there is a change in magnetic field due to coil A, an emf will be induced in the coil B. When the key is closed, the current starts increasing from zero to maximum. Thus the magnetic field also increases and an emf is produced in the nearby key in this case.

Electric generators also known as Dynamos convert mechanical energy into electrical energy and work on the principle of electromagnetic induction. The principle of electromagnetic induction states that the change in the magnetic field around a conductor generates electric current in the circuit. Generators 2 types - DC generator (Dynamo) and AC generator (Alternator).

The solenoid is a type of electromagnet, the purpose of which is to generate a controlled magnetic field through a coil wound into a tightly packed helix. Magnetic field due to a straight current-carrying conductor - When current is passed through it, a magnetic field is produced around it. Magnetic field due to current through a circular loop - Every point on the wire carrying current gives rise to a magnetic field that appears as straight lines at the center of the loop. Loudspeaker, Voltmeter, Ammeter, based on the concept of force on a current-carrying conductor in a magnetic field.

(Related to Faraday’s Law of Electromagnetic Induction). Michael Faraday discovered electromagnetic induction in 1831. Electrical devices which are based on the phenomenon of magnetic induction - the electric generator, the electric motor, and the transformer.

A magnetic field created by a nearby magnet will exert a force on a current-carrying conductor. Its direction can be identified using Fleming's left-hand rule which states that if the forefinger of the left-hand points in the direction of the magnetic field, the middle finger points in the current direction, then the thumb points in the direction of the force.