Railway Science (Physics-Work, Energy and Power)

There are three types of sound waves: Infrasonic sounds - waves below the frequency of 20Hz. Sonic Waves - Human beings can only hear sounds whose frequency is ranging from 20Hz to 20kHz. Ultrasonic sounds - above the frequency of 20kHz. It can be reflected back from defective locations. Example - Bats are good at flying at night because they use ultrasonic sound.

(SI unit - watt) is a scalar quantity as it has only magnitude and no direction. Examples of Scalar Quantity - Distance, Speed, Mass, Temperature, Energy, Work, Volume, Area. Vector Quantities : These are the quantities which have magnitude as well as direction. Examples of Vector Quantities - Linear Momentum, Acceleration, Displacement, Momentum, Angular velocity, Force, Electric field.

by rotating a coil of wire in a magnetic field this creates an electric current in the wire. Electric motors are the opposite of dynamos. They convert electrical energy into mechanical energy. Batteries store and provide electrical energy. Photocells convert light energy into electrical energy, primarily through the photovoltaic effect.

Kinetic energy of the gas molecules: The energy possessed by the molecule of the gas due to its motion. The pressure in a gas develops due to the collisions between the gaseous molecules. Formulae:

Energy is the ability to do work. Electrical energy is the energy generated by the movement of electrons from one point to another. The movement of charged particles along/through a medium (say wire) constitutes current or electricity. Ohm’s law - discovered by G.S. Ohm. The SI units : Electrical energy - joule (J), Electric current - ampere (A), Electric potential difference - volt (V), Electric resistance - ohm (Ω).

Kinetic energy - The energy possessed by a body due to its motion. The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of the substance. Unit of Kinetic Energy - Joule. Kelvin(K) is the SI unit of temperature. Potential energy - The energy that is stored in an object due to its position relative to some zero position.

Power is the measurement of energy transfer by an electrical circuit in unit time. Unit - watt (W). Electrical Power - Rate at which electrical energy is consumed by an electrical appliance. Power in DC circuit (P) = V × I, P = I²R, P = 𝑉²/R, where V= Voltage, I = Current and R = Resistance. Power in AC circuit (P) = VI cos ø, where cos ø = Power factor. Electrical Energy - Capacity for doing electrical work. Electrical Energy (E) = Power (P) × Time (T).

Fuel - The sources of energy for domestic and industrial purposes are mainly wood, charcoal, petrol, kerosene, etc. The efficiency of the fuel is measured by its calorific value. Calorific value - The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value. Fuel gives energy by burning (combustion). More calorific value, more efficient fuel.

The energy obtained by an object by virtue of its motion. Formula : 𝐾 = - 1/2   𝑚𝑣² where K - kinetic energy, v - speed of the object, m - mass of the object. Potential Energy: The energy of an object obtained by doing work against the conservative forces like spring force and gravitational force. Electrical energy - The energy generated by the movement of electrons from one point to another.

The energy stored in the bonds of atoms and molecules. Examples - Batteries, biomass, petroleum, natural gas, and coal. In thermal power plants, the fuel is burnt to produce heat energy which is converted into electrical energy. Hydro-electric energy - The conversion of the potential energy of falling water into electricity. Tidal energy - A renewable energy powered by the natural rise and fall of ocean tides and currents.