Railway Science (Physics-Electric Current and its Effects)

Parallel combination: When the electric current has multiple paths to flow through. The components that are a part of the parallel circuits would have a constant voltage across all ends. If there are ‘n’ resistors, each of them connected in a parallel combination then having resistances R₁ , R₂ , R₃ , R₄….. Rn . Then their net resistance would be given as; 1/Rₙₑₜ = 1/R₁ + 1/R₂ + 1/R₃ + 1/R₄ …….. + 1/Rₙ .

Properties of Good conductor: A conductor always allows the movement of electrons and ions through them; The electric field inside a conductor is zero allowing electrons to flow within them; The charge density inside a conductor is zero; Electric conductors should have a low resistance to electricity flow in general. An ideal conductor should have zero resistance.

Properties of a magnet: Directive property - If a magnet is suspended freely in air then it always aligns itself in the geographic north-south direction), Repulsive Property - It is used to determine whether a certain rod is magnetic repulsion between the iron rod and the magnet, Attractive property - It is property of magnet that attracts ferromagnetic materials like iron, cobalt, and nickel.

A potential difference can be induced (created) in a conductor when there is movement between the conductor and a magnetic field. This can occur in different ways - A coil of wire is moved in a magnetic field, A magnet is moved into a coil of wire. To increase the magnitude of potential difference - Move the magnet faster, Use a stronger magnet, Increase the number of turns on the coil. To increase the magnitude of the induced current - Increase the number of turns in the coil

Magnitude of the magnetic field produced inside a solenoid is B = (𝜇ₒ ni) /𝑙 . where i is the current of the solenoid, n is the number of turns the solenoid has, l is the length of the solenoid, and 𝜇ₒ (permeability of free space) = 4𝜋 × 10⁻⁷ T·m/A. So, B depends upon ‘n’ , ‘i’ and ‘𝑙’

The direction of the magnetic field is taken to be the direction in which a north pole of the compass needle moves inside it. Therefore it is taken by convention that the field lines emerge from the north pole and merge at the south pole. Direction of Magnetic field lines - North pole to South pole (outside the magnet) and South pole to North pole (inside the magnet).

The phenomenon of electromagnetic induction is observed during the interval the key is taken out because initially there was a steady current flow, but whenever the key plugged out, the current decreased to zero. This change in current causes a change in magnetic field in coil A. Thus there will be an emf induced in the coil B and the galvanometer will get deflected.

Faraday’s law of electromagnetic induction, is the basic law of electromagnetism which helps to predict how a magnetic field would interact with an electric circuit to produce an electromotive force (EMF).

Electrical resistivity - Fundamental property of a material that measures how strongly it resists electric current. Metals are good electrical conductors (high conductivity and low resistivity), while non-metals are mostly poor conductors (low conductivity and high resistivity). Manganin - Alloy of Copper (Cu), Manganese (Mn), and Nickel (Ni). Nichrome has the maximum electrical resistivity

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 centre. Magnetic Field due to a Current in a Solenoid - magnetic field is set up around a solenoid similar to the bar magnet.