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

Insulators are materials that do not allow electricity to pass easily through them, such as plastic, paper, glass, and dry air, etc. At high temperatures, the conductor resistivity increases and conductivity decreases.

The amount of work done in moving a unit positive charge without acceleration from one point to another along any path between the two points. Electric current - The rate of flow of electrons in a conductor. SI Unit - Ampere. Air resistance - A force that is caused due to air when an object moves through it. Magnetic induction (electromagnetic induction) - The production of voltage across an electrical conductor placed inside a varying magnetic field.

When two objects are linked by a conducting wire, electrons can move freely between them. But if both objects have equal potential, there's no potential difference driving the flow of electrons. Electric current is the movement of charged particles from higher to lower potential.

Chemical effect : The passage of an electric current through a conducting solution causes chemical reactions. As a result, bubbles of a gas may be formed on the electrodes. Deposits of metal may be seen on electrodes. Changes of colour of solutions may occur. Heating effect: When an electric current flows through a wire, the wire gets heated. It is the heating effect of current. Magnetic effect of electric current: When an electric current flows through a wire, it behaves like a magnet.

(symbol W, Atomic number 74). Its melting point is 3380⁰ C. Tungsten filament lamps are filled with Nitrogen or argon gas. Iron (Symbol Fe, atomic number 26), Silver (symbol Ag, atomic number 47), Nickel (symbol Ni, atomic number 28).

A variable resistor which is used for controlling the flow of electric current either by increasing or decreasing the resistance. A rheostat is connected in series because the current flows through the path where the resistance is minimum.

Resistivity: A measure of the resistance of a specific material to conduct electricity. It is represented by ρ. Resistivity or specific resistance of a material is an intrinsic property and depends only on the material and temperature.

The factors which affect the resistance of a conductor are resistivity, temperature, length, and area of cross section. Temperature is directly proportional to resistance. The higher the temperature, the higher is the resistivity. Length of the conductor is directly proportional to resistance.

Cell - A single anode and cathode separated by an electrolyte. This device that converts chemical energy into electrical energy. Batteries - Composed of one or more cells, each containing a positive electrode, a negative electrode, separator, and electrolyte. Primary Cell - produces current by irreversible chemical reactions and is not rechargeable. Examples: Leclanche Cell, Daniel Cell, Dry Cell. Alessandro Volta - Invented the electric cell.

Resistivity, ρ (Ω m) of some materials: Conductors - Silver 1.6 × 10⁻⁸ , Copper 1.62 × 10⁻⁸ , Aluminium 2.6 × 10⁻⁸ , Tungsten 5.2 × 10⁻⁸ , Iron 10 × 10⁻⁸ , Platinum 11 × 10⁻⁸ , Mercury 94 × 10⁻⁸ .