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

It is the region around a magnetic material or a moving electric charge within which the force of magnetism acts. Unit- Tesla or (Newton.Second)/Coulomb.
Electrostatic field: An electric field is a region around a charged object where an electric force can be applied to another charged object. SI unit- volts per metre (V/m).

circuit total resistance is: R = R₁ + R₂ + R₃ +... If one of the series paths is broken, current does not flow in all the other paths. A parallel circuit has two or more paths for current to flow through. Total resistance in a Parallel circuit  1/𝑅 = 1/𝑅₁ + 1/R₂ + 1/𝑅₃ + ... If one of the parallel paths is broken, current will continue to flow in all the other paths.

Electrical resistivity is the reciprocal of electrical conductivity. It is the measure of the ability of a material to oppose the flow of current. Metals are good conductors of electricity. Hence, they have low resistivity. The insulators like rubber, glass, graphite, plastics, etc., have very high resistivity when compared to the metallic conductors. The third type is the semiconductor which comes in between the conductors and insulators. Their resistivity decreases with the increase in temperature and is also affected by the presence of impurities in them.

The electric generator works on the principle of electromagnetic induction which is known as the faraday law. When a coil is rotated in the presence of a uniform magnetic field, the current is induced in it.

Equal resistances in parallel corresponds to equal current in each branch. When two or more resistances are connected one after another such that the same current flows through them are called as resistances in series. Resistance is a measure of the opposition to current flow in an electrical circuit. The SI units is ohm (Ω).

Resistance of the conductor is proportional to the length of wire and inversely proportional to the area of cross-section. Resistance of the conductor (R) = ρ  𝑙/𝐴 , R ∝  𝑙/𝐴 . Where ρ is the resistivity of the conductor, L is its length and A is the cross sectional area of the conductor. Electrical Resistivity is a measure of how strongly it opposes the flow of current. It is denoted by the symbol "ρ" (rho) and is measured in ohm-meters (Ω·m).

Ohm’s law - The voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperatures remain constant. V ∝ I, V = IR (Where V = Voltage, I = Current, R = Resistance), I = V/R (Current is inversely proportional to resistance. This means that as the resistance increases, current decreases, and if the resistance decreases, current increases.)

The force of attraction or repulsion between two point charges is directly proportional to the product of the charges and Inversely proportional to the square of the distance between them. F = ke 𝑞₁𝑞₂/r²
Where {kₑ is Coulomb's constant (9 × 10⁹Nm²c⁻²). q₁ and q₂ are the signed magnitudes of the charges and r is the distance between the charges}.

Coulomb's Law Formula (F)
= k 𝑞₁𝑞₂/r² , Where, F is the Coulomb force expressed in Newtons (N), q₁ is the first point charge expressed in Coulombs (C), q₂ is the second point charge (C), r is the distance between two point charge in meters (m), k (8.99 × 10⁹ N ⋅ m²/C²) is an electrostatic constant.

Insulator - It is a material which does not easily allow heat and electricity to pass through it; Examples - Plastic, wood, rubber and glass; Properties - Do not have free electrons to conduct electricity, High resistivity, Large dielectric strength, high air permeability.